Add m-esr52 at 52.6.0

1 files changed, 7553 insertions, 0 deletions

diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
new file mode 100644
index 000000000..8035269e3
--- /dev/null
+++ b/layout/base/nsDisplayList.cpp
@@ -0,0 +1,7553 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=2 sw=2 et tw=78:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/*
+ * structures that represent things to be painted (ordered in z-order),
+ * used during painting and hit testing
+ */
+
+#include "nsDisplayList.h"
+
+#include <stdint.h>
+#include <algorithm>
+#include <limits>
+
+#include "gfxUtils.h"
+#include "mozilla/dom/TabChild.h"
+#include "mozilla/dom/KeyframeEffectReadOnly.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/layers/PLayerTransaction.h"
+#include "nsCSSRendering.h"
+#include "nsRenderingContext.h"
+#include "nsISelectionController.h"
+#include "nsIPresShell.h"
+#include "nsRegion.h"
+#include "nsStyleStructInlines.h"
+#include "nsStyleTransformMatrix.h"
+#include "gfxMatrix.h"
+#include "gfxPrefs.h"
+#include "nsSVGIntegrationUtils.h"
+#include "nsSVGUtils.h"
+#include "nsLayoutUtils.h"
+#include "nsIScrollableFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsThemeConstants.h"
+#include "LayerTreeInvalidation.h"
+
+#include "imgIContainer.h"
+#include "BasicLayers.h"
+#include "nsBoxFrame.h"
+#include "nsViewportFrame.h"
+#include "nsSubDocumentFrame.h"
+#include "nsSVGEffects.h"
+#include "nsSVGElement.h"
+#include "nsSVGClipPathFrame.h"
+#include "GeckoProfiler.h"
+#include "nsViewManager.h"
+#include "ImageLayers.h"
+#include "ImageContainer.h"
+#include "nsCanvasFrame.h"
+#include "StickyScrollContainer.h"
+#include "mozilla/AnimationPerformanceWarning.h"
+#include "mozilla/AnimationUtils.h"
+#include "mozilla/EffectCompositor.h"
+#include "mozilla/EffectSet.h"
+#include "mozilla/EventStates.h"
+#include "mozilla/LookAndFeel.h"
+#include "mozilla/OperatorNewExtensions.h"
+#include "mozilla/PendingAnimationTracker.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/gfx/gfxVars.h"
+#include "ActiveLayerTracker.h"
+#include "nsContentUtils.h"
+#include "nsPrintfCString.h"
+#include "UnitTransforms.h"
+#include "LayersLogging.h"
+#include "FrameLayerBuilder.h"
+#include "mozilla/EventStateManager.h"
+#include "mozilla/RestyleManager.h"
+#include "nsCaret.h"
+#include "nsISelection.h"
+#include "nsDOMTokenList.h"
+#include "mozilla/RuleNodeCacheConditions.h"
+#include "nsCSSProps.h"
+#include "nsPluginFrame.h"
+#include "DisplayItemScrollClip.h"
+#include "nsSVGMaskFrame.h"
+
+// GetCurrentTime is defined in winbase.h as zero argument macro forwarding to
+// GetTickCount().
+#ifdef GetCurrentTime
+#undef GetCurrentTime
+#endif
+
+using namespace mozilla;
+using namespace mozilla::layers;
+using namespace mozilla::dom;
+using namespace mozilla::layout;
+using namespace mozilla::gfx;
+
+typedef FrameMetrics::ViewID ViewID;
+typedef nsStyleTransformMatrix::TransformReferenceBox TransformReferenceBox;
+
+#ifdef DEBUG
+static bool
+SpammyLayoutWarningsEnabled()
+{
+  static bool sValue = false;
+  static bool sValueInitialized = false;
+
+  if (!sValueInitialized) {
+    Preferences::GetBool("layout.spammy_warnings.enabled", &sValue);
+    sValueInitialized = true;
+  }
+
+  return sValue;
+}
+#endif
+
+void*
+AnimatedGeometryRoot::operator new(size_t aSize, nsDisplayListBuilder* aBuilder)
+{
+  return aBuilder->Allocate(aSize);
+}
+
+static inline CSSAngle
+MakeCSSAngle(const nsCSSValue& aValue)
+{
+  return CSSAngle(aValue.GetAngleValue(), aValue.GetUnit());
+}
+
+static void AddTransformFunctions(nsCSSValueList* aList,
+                                  nsStyleContext* aContext,
+                                  nsPresContext* aPresContext,
+                                  TransformReferenceBox& aRefBox,
+                                  InfallibleTArray<TransformFunction>& aFunctions)
+{
+  if (aList->mValue.GetUnit() == eCSSUnit_None) {
+    return;
+  }
+
+  for (const nsCSSValueList* curr = aList; curr; curr = curr->mNext) {
+    const nsCSSValue& currElem = curr->mValue;
+    NS_ASSERTION(currElem.GetUnit() == eCSSUnit_Function,
+                 "Stream should consist solely of functions!");
+    nsCSSValue::Array* array = currElem.GetArrayValue();
+    RuleNodeCacheConditions conditions;
+    switch (nsStyleTransformMatrix::TransformFunctionOf(array)) {
+      case eCSSKeyword_rotatex:
+      {
+        CSSAngle theta = MakeCSSAngle(array->Item(1));
+        aFunctions.AppendElement(RotationX(theta));
+        break;
+      }
+      case eCSSKeyword_rotatey:
+      {
+        CSSAngle theta = MakeCSSAngle(array->Item(1));
+        aFunctions.AppendElement(RotationY(theta));
+        break;
+      }
+      case eCSSKeyword_rotatez:
+      {
+        CSSAngle theta = MakeCSSAngle(array->Item(1));
+        aFunctions.AppendElement(RotationZ(theta));
+        break;
+      }
+      case eCSSKeyword_rotate:
+      {
+        CSSAngle theta = MakeCSSAngle(array->Item(1));
+        aFunctions.AppendElement(Rotation(theta));
+        break;
+      }
+      case eCSSKeyword_rotate3d:
+      {
+        double x = array->Item(1).GetFloatValue();
+        double y = array->Item(2).GetFloatValue();
+        double z = array->Item(3).GetFloatValue();
+        CSSAngle theta = MakeCSSAngle(array->Item(4));
+        aFunctions.AppendElement(Rotation3D(x, y, z, theta));
+        break;
+      }
+      case eCSSKeyword_scalex:
+      {
+        double x = array->Item(1).GetFloatValue();
+        aFunctions.AppendElement(Scale(x, 1, 1));
+        break;
+      }
+      case eCSSKeyword_scaley:
+      {
+        double y = array->Item(1).GetFloatValue();
+        aFunctions.AppendElement(Scale(1, y, 1));
+        break;
+      }
+      case eCSSKeyword_scalez:
+      {
+        double z = array->Item(1).GetFloatValue();
+        aFunctions.AppendElement(Scale(1, 1, z));
+        break;
+      }
+      case eCSSKeyword_scale:
+      {
+        double x = array->Item(1).GetFloatValue();
+        // scale(x) is shorthand for scale(x, x);
+        double y = array->Count() == 2 ? x : array->Item(2).GetFloatValue();
+        aFunctions.AppendElement(Scale(x, y, 1));
+        break;
+      }
+      case eCSSKeyword_scale3d:
+      {
+        double x = array->Item(1).GetFloatValue();
+        double y = array->Item(2).GetFloatValue();
+        double z = array->Item(3).GetFloatValue();
+        aFunctions.AppendElement(Scale(x, y, z));
+        break;
+      }
+      case eCSSKeyword_translatex:
+      {
+        double x = nsStyleTransformMatrix::ProcessTranslatePart(
+          array->Item(1), aContext, aPresContext, conditions,
+          &aRefBox, &TransformReferenceBox::Width);
+        aFunctions.AppendElement(Translation(x, 0, 0));
+        break;
+      }
+      case eCSSKeyword_translatey:
+      {
+        double y = nsStyleTransformMatrix::ProcessTranslatePart(
+          array->Item(1), aContext, aPresContext, conditions,
+          &aRefBox, &TransformReferenceBox::Height);
+        aFunctions.AppendElement(Translation(0, y, 0));
+        break;
+      }
+      case eCSSKeyword_translatez:
+      {
+        double z = nsStyleTransformMatrix::ProcessTranslatePart(
+          array->Item(1), aContext, aPresContext, conditions,
+          nullptr);
+        aFunctions.AppendElement(Translation(0, 0, z));
+        break;
+      }
+      case eCSSKeyword_translate:
+      {
+        double x = nsStyleTransformMatrix::ProcessTranslatePart(
+          array->Item(1), aContext, aPresContext, conditions,
+          &aRefBox, &TransformReferenceBox::Width);
+        // translate(x) is shorthand for translate(x, 0)
+        double y = 0;
+        if (array->Count() == 3) {
+           y = nsStyleTransformMatrix::ProcessTranslatePart(
+            array->Item(2), aContext, aPresContext, conditions,
+            &aRefBox, &TransformReferenceBox::Height);
+        }
+        aFunctions.AppendElement(Translation(x, y, 0));
+        break;
+      }
+      case eCSSKeyword_translate3d:
+      {
+        double x = nsStyleTransformMatrix::ProcessTranslatePart(
+          array->Item(1), aContext, aPresContext, conditions,
+          &aRefBox, &TransformReferenceBox::Width);
+        double y = nsStyleTransformMatrix::ProcessTranslatePart(
+          array->Item(2), aContext, aPresContext, conditions,
+          &aRefBox, &TransformReferenceBox::Height);
+        double z = nsStyleTransformMatrix::ProcessTranslatePart(
+          array->Item(3), aContext, aPresContext, conditions,
+          nullptr);
+
+        aFunctions.AppendElement(Translation(x, y, z));
+        break;
+      }
+      case eCSSKeyword_skewx:
+      {
+        CSSAngle x = MakeCSSAngle(array->Item(1));
+        aFunctions.AppendElement(SkewX(x));
+        break;
+      }
+      case eCSSKeyword_skewy:
+      {
+        CSSAngle y = MakeCSSAngle(array->Item(1));
+        aFunctions.AppendElement(SkewY(y));
+        break;
+      }
+      case eCSSKeyword_skew:
+      {
+        CSSAngle x = MakeCSSAngle(array->Item(1));
+        // skew(x) is shorthand for skew(x, 0)
+        CSSAngle y(0.0f, eCSSUnit_Degree);
+        if (array->Count() == 3) {
+          y = MakeCSSAngle(array->Item(2));
+        }
+        aFunctions.AppendElement(Skew(x, y));
+        break;
+      }
+      case eCSSKeyword_matrix:
+      {
+        gfx::Matrix4x4 matrix;
+        matrix._11 = array->Item(1).GetFloatValue();
+        matrix._12 = array->Item(2).GetFloatValue();
+        matrix._13 = 0;
+        matrix._14 = 0;
+        matrix._21 = array->Item(3).GetFloatValue();
+        matrix._22 = array->Item(4).GetFloatValue();
+        matrix._23 = 0;
+        matrix._24 = 0;
+        matrix._31 = 0;
+        matrix._32 = 0;
+        matrix._33 = 1;
+        matrix._34 = 0;
+        matrix._41 = array->Item(5).GetFloatValue();
+        matrix._42 = array->Item(6).GetFloatValue();
+        matrix._43 = 0;
+        matrix._44 = 1;
+        aFunctions.AppendElement(TransformMatrix(matrix));
+        break;
+      }
+      case eCSSKeyword_matrix3d:
+      {
+        gfx::Matrix4x4 matrix;
+        matrix._11 = array->Item(1).GetFloatValue();
+        matrix._12 = array->Item(2).GetFloatValue();
+        matrix._13 = array->Item(3).GetFloatValue();
+        matrix._14 = array->Item(4).GetFloatValue();
+        matrix._21 = array->Item(5).GetFloatValue();
+        matrix._22 = array->Item(6).GetFloatValue();
+        matrix._23 = array->Item(7).GetFloatValue();
+        matrix._24 = array->Item(8).GetFloatValue();
+        matrix._31 = array->Item(9).GetFloatValue();
+        matrix._32 = array->Item(10).GetFloatValue();
+        matrix._33 = array->Item(11).GetFloatValue();
+        matrix._34 = array->Item(12).GetFloatValue();
+        matrix._41 = array->Item(13).GetFloatValue();
+        matrix._42 = array->Item(14).GetFloatValue();
+        matrix._43 = array->Item(15).GetFloatValue();
+        matrix._44 = array->Item(16).GetFloatValue();
+        aFunctions.AppendElement(TransformMatrix(matrix));
+        break;
+      }
+      case eCSSKeyword_interpolatematrix:
+      {
+        bool dummy;
+        Matrix4x4 matrix;
+        nsStyleTransformMatrix::ProcessInterpolateMatrix(matrix, array,
+                                                         aContext,
+                                                         aPresContext,
+                                                         conditions,
+                                                         aRefBox,
+                                                         &dummy);
+        aFunctions.AppendElement(TransformMatrix(matrix));
+        break;
+      }
+      case eCSSKeyword_perspective:
+      {
+        aFunctions.AppendElement(Perspective(array->Item(1).GetFloatValue()));
+        break;
+      }
+      default:
+        NS_ERROR("Function not handled yet!");
+    }
+  }
+}
+
+static TimingFunction
+ToTimingFunction(const Maybe<ComputedTimingFunction>& aCTF)
+{
+  if (aCTF.isNothing()) {
+    return TimingFunction(null_t());
+  }
+
+  if (aCTF->HasSpline()) {
+    const nsSMILKeySpline* spline = aCTF->GetFunction();
+    return TimingFunction(CubicBezierFunction(spline->X1(), spline->Y1(),
+                                              spline->X2(), spline->Y2()));
+  }
+
+  uint32_t type = aCTF->GetType() == nsTimingFunction::Type::StepStart ? 1 : 2;
+  return TimingFunction(StepFunction(aCTF->GetSteps(), type));
+}
+
+static void
+AddAnimationForProperty(nsIFrame* aFrame, const AnimationProperty& aProperty,
+                        dom::Animation* aAnimation, Layer* aLayer,
+                        AnimationData& aData, bool aPending)
+{
+  MOZ_ASSERT(aLayer->AsContainerLayer(), "Should only animate ContainerLayer");
+  MOZ_ASSERT(aAnimation->GetEffect(),
+             "Should not be adding an animation without an effect");
+  MOZ_ASSERT(!aAnimation->GetCurrentOrPendingStartTime().IsNull() ||
+             (aAnimation->GetTimeline() &&
+              aAnimation->GetTimeline()->TracksWallclockTime()),
+             "Animation should either have a resolved start time or "
+             "a timeline that tracks wallclock time");
+  nsStyleContext* styleContext = aFrame->StyleContext();
+  nsPresContext* presContext = aFrame->PresContext();
+  TransformReferenceBox refBox(aFrame);
+
+  layers::Animation* animation =
+    aPending ?
+    aLayer->AddAnimationForNextTransaction() :
+    aLayer->AddAnimation();
+
+  const TimingParams& timing = aAnimation->GetEffect()->SpecifiedTiming();
+
+  // If we are starting a new transition that replaces an existing transition
+  // running on the compositor, it is possible that the animation on the
+  // compositor will have advanced ahead of the main thread. If we use as
+  // the starting point of the new transition, the current value of the
+  // replaced transition as calculated on the main thread using the refresh
+  // driver time, the new transition will jump when it starts. Instead, we
+  // re-calculate the starting point of the new transition by applying the
+  // current TimeStamp to the parameters of the replaced transition.
+  //
+  // We need to do this here, rather than when we generate the new transition,
+  // since after generating the new transition other requestAnimationFrame
+  // callbacks may run that introduce further lag between the main thread and
+  // the compositor.
+  if (aAnimation->AsCSSTransition() &&
+      aAnimation->GetEffect() &&
+      aAnimation->GetEffect()->AsTransition()) {
+    // We update startValue from the replaced transition only if the effect is
+    // an ElementPropertyTransition.
+    aAnimation->GetEffect()->AsTransition()->
+      UpdateStartValueFromReplacedTransition();
+  }
+
+  const ComputedTiming computedTiming =
+    aAnimation->GetEffect()->GetComputedTiming();
+  Nullable<TimeDuration> startTime = aAnimation->GetCurrentOrPendingStartTime();
+  animation->startTime() = startTime.IsNull()
+                           ? TimeStamp()
+                           : aAnimation->GetTimeline()->
+                              ToTimeStamp(startTime.Value());
+  animation->initialCurrentTime() = aAnimation->GetCurrentTime().Value()
+                                    - timing.mDelay;
+  animation->delay() = timing.mDelay;
+  animation->duration() = computedTiming.mDuration;
+  animation->iterations() = computedTiming.mIterations;
+  animation->iterationStart() = computedTiming.mIterationStart;
+  animation->direction() = static_cast<uint8_t>(timing.mDirection);
+  animation->fillMode() = static_cast<uint8_t>(computedTiming.mFill);
+  animation->property() = aProperty.mProperty;
+  animation->playbackRate() = aAnimation->PlaybackRate();
+  animation->data() = aData;
+  animation->easingFunction() = ToTimingFunction(timing.mFunction);
+  animation->iterationComposite() =
+    static_cast<uint8_t>(aAnimation->GetEffect()->
+                         AsKeyframeEffect()->IterationComposite());
+
+  for (uint32_t segIdx = 0; segIdx < aProperty.mSegments.Length(); segIdx++) {
+    const AnimationPropertySegment& segment = aProperty.mSegments[segIdx];
+
+    AnimationSegment* animSegment = animation->segments().AppendElement();
+    if (aProperty.mProperty == eCSSProperty_transform) {
+      animSegment->startState() = InfallibleTArray<TransformFunction>();
+      animSegment->endState() = InfallibleTArray<TransformFunction>();
+
+      nsCSSValueSharedList* list =
+        segment.mFromValue.GetCSSValueSharedListValue();
+      AddTransformFunctions(list->mHead, styleContext, presContext, refBox,
+                            animSegment->startState().get_ArrayOfTransformFunction());
+
+      list = segment.mToValue.GetCSSValueSharedListValue();
+      AddTransformFunctions(list->mHead, styleContext, presContext, refBox,
+                            animSegment->endState().get_ArrayOfTransformFunction());
+    } else if (aProperty.mProperty == eCSSProperty_opacity) {
+      animSegment->startState() = segment.mFromValue.GetFloatValue();
+      animSegment->endState() = segment.mToValue.GetFloatValue();
+    }
+
+    animSegment->startPortion() = segment.mFromKey;
+    animSegment->endPortion() = segment.mToKey;
+    animSegment->sampleFn() = ToTimingFunction(segment.mTimingFunction);
+  }
+}
+
+static void
+AddAnimationsForProperty(nsIFrame* aFrame, nsCSSPropertyID aProperty,
+                         nsTArray<RefPtr<dom::Animation>>& aAnimations,
+                         Layer* aLayer, AnimationData& aData,
+                         bool aPending)
+{
+  MOZ_ASSERT(nsCSSProps::PropHasFlags(aProperty,
+                                      CSS_PROPERTY_CAN_ANIMATE_ON_COMPOSITOR),
+             "inconsistent property flags");
+
+  DebugOnly<EffectSet*> effects = EffectSet::GetEffectSet(aFrame);
+  MOZ_ASSERT(effects);
+
+  // Add from first to last (since last overrides)
+  for (size_t animIdx = 0; animIdx < aAnimations.Length(); animIdx++) {
+    dom::Animation* anim = aAnimations[animIdx];
+    if (!anim->IsPlayableOnCompositor()) {
+      continue;
+    }
+
+    dom::KeyframeEffectReadOnly* keyframeEffect =
+      anim->GetEffect() ? anim->GetEffect()->AsKeyframeEffect() : nullptr;
+    MOZ_ASSERT(keyframeEffect,
+               "A playing animation should have a keyframe effect");
+    const AnimationProperty* property =
+      keyframeEffect->GetEffectiveAnimationOfProperty(aProperty);
+    if (!property) {
+      continue;
+    }
+
+    // Note that if the property is overridden by !important rules,
+    // GetEffectiveAnimationOfProperty returns null instead.
+    // This is what we want, since if we have animations overridden by
+    // !important rules, we don't want to send them to the compositor.
+    MOZ_ASSERT(anim->CascadeLevel() !=
+                 EffectCompositor::CascadeLevel::Animations ||
+               !effects->PropertiesWithImportantRules()
+                  .HasProperty(aProperty),
+               "GetEffectiveAnimationOfProperty already tested the property "
+               "is not overridden by !important rules");
+
+    // Don't add animations that are pending if their timeline does not
+    // track wallclock time. This is because any pending animations on layers
+    // will have their start time updated with the current wallclock time.
+    // If we can't convert that wallclock time back to an equivalent timeline
+    // time, we won't be able to update the content animation and it will end
+    // up being out of sync with the layer animation.
+    //
+    // Currently this only happens when the timeline is driven by a refresh
+    // driver under test control. In this case, the next time the refresh
+    // driver is advanced it will trigger any pending animations.
+    if (anim->PlayState() == AnimationPlayState::Pending &&
+        (!anim->GetTimeline() ||
+         !anim->GetTimeline()->TracksWallclockTime())) {
+      continue;
+    }
+
+    AddAnimationForProperty(aFrame, *property, anim, aLayer, aData, aPending);
+    keyframeEffect->SetIsRunningOnCompositor(aProperty, true);
+  }
+}
+
+static bool
+GenerateAndPushTextMask(nsIFrame* aFrame, nsRenderingContext* aContext,
+                        const nsRect& aFillRect, nsDisplayListBuilder* aBuilder)
+{
+  if (aBuilder->IsForGenerateGlyphMask() ||
+      aBuilder->IsForPaintingSelectionBG()) {
+    return false;
+  }
+
+  // The main function of enabling background-clip:text property value.
+  // When a nsDisplayBackgroundImage detects "text" bg-clip style, it will call
+  // this function to
+  // 1. Paint background color of the selection text if any.
+  // 2. Generate a mask by all descendant text frames
+  // 3. Push the generated mask into aContext.
+  //
+  // TBD: we actually generate display list of aFrame twice here. It's better
+  // to reuse the same display list and paint that one twice, one for selection
+  // background, one for generating text mask.
+
+  gfxContext* sourceCtx = aContext->ThebesContext();
+  gfxRect bounds =
+    nsLayoutUtils::RectToGfxRect(aFillRect,
+                                 aFrame->PresContext()->AppUnitsPerDevPixel());
+
+  {
+    // Paint text selection background into sourceCtx.
+    gfxContextMatrixAutoSaveRestore save(sourceCtx);
+    sourceCtx->SetMatrix(sourceCtx->CurrentMatrix().Translate(bounds.TopLeft()));
+
+    nsLayoutUtils::PaintFrame(aContext, aFrame,
+                              nsRect(nsPoint(0, 0), aFrame->GetSize()),
+                              NS_RGB(255, 255, 255),
+                              nsDisplayListBuilderMode::PAINTING_SELECTION_BACKGROUND);
+  }
+
+  // Evaluate required surface size.
+  IntRect drawRect;
+  {
+    gfxContextMatrixAutoSaveRestore matRestore(sourceCtx);
+
+    sourceCtx->SetMatrix(gfxMatrix());
+    gfxRect clipRect = sourceCtx->GetClipExtents();
+    drawRect = RoundedOut(ToRect(clipRect));
+  }
+
+  // Create a mask surface.
+  RefPtr<DrawTarget> sourceTarget = sourceCtx->GetDrawTarget();
+  RefPtr<DrawTarget> maskDT =
+    sourceTarget->CreateSimilarDrawTarget(drawRect.Size(),
+                                          SurfaceFormat::A8);
+  if (!maskDT || !maskDT->IsValid()) {
+    return false;
+  }
+  RefPtr<gfxContext> maskCtx = gfxContext::CreatePreservingTransformOrNull(maskDT);
+  MOZ_ASSERT(maskCtx);
+  gfxMatrix currentMatrix = sourceCtx->CurrentMatrix();
+  maskCtx->SetMatrix(gfxMatrix::Translation(bounds.TopLeft()) *
+                     currentMatrix *
+                     gfxMatrix::Translation(-drawRect.TopLeft()));
+
+  // Shade text shape into mask A8 surface.
+  nsRenderingContext rc(maskCtx);
+  nsLayoutUtils::PaintFrame(&rc, aFrame,
+                            nsRect(nsPoint(0, 0), aFrame->GetSize()),
+                            NS_RGB(255, 255, 255),
+                            nsDisplayListBuilderMode::GENERATE_GLYPH);
+
+  // Push the generated mask into aContext, so that the caller can pop and
+  // blend with it.
+  Matrix maskTransform = ToMatrix(currentMatrix) *
+                         Matrix::Translation(-drawRect.x, -drawRect.y);
+  maskTransform.Invert();
+
+  RefPtr<SourceSurface> maskSurface = maskDT->Snapshot();
+  sourceCtx->PushGroupForBlendBack(gfxContentType::COLOR_ALPHA, 1.0, maskSurface, maskTransform);
+
+  return true;
+}
+
+/* static */ void
+nsDisplayListBuilder::AddAnimationsAndTransitionsToLayer(Layer* aLayer,
+                                                         nsDisplayListBuilder* aBuilder,
+                                                         nsDisplayItem* aItem,
+                                                         nsIFrame* aFrame,
+                                                         nsCSSPropertyID aProperty)
+{
+  MOZ_ASSERT(nsCSSProps::PropHasFlags(aProperty,
+                                      CSS_PROPERTY_CAN_ANIMATE_ON_COMPOSITOR),
+             "inconsistent property flags");
+
+  // This function can be called in two ways:  from
+  // nsDisplay*::BuildLayer while constructing a layer (with all
+  // pointers non-null), or from RestyleManager's handling of
+  // UpdateOpacityLayer/UpdateTransformLayer hints.
+  MOZ_ASSERT(!aBuilder == !aItem,
+             "should only be called in two configurations, with both "
+             "aBuilder and aItem, or with neither");
+  MOZ_ASSERT(!aItem || aFrame == aItem->Frame(), "frame mismatch");
+
+  // Only send animations to a layer that is actually using
+  // off-main-thread compositing.
+  if (aLayer->Manager()->GetBackendType() !=
+        layers::LayersBackend::LAYERS_CLIENT) {
+    return;
+  }
+
+  bool pending = !aBuilder;
+
+  if (pending) {
+    aLayer->ClearAnimationsForNextTransaction();
+  } else {
+    aLayer->ClearAnimations();
+  }
+
+  // Update the animation generation on the layer. We need to do this before
+  // any early returns since even if we don't add any animations to the
+  // layer, we still need to mark it as up-to-date with regards to animations.
+  // Otherwise, in RestyleManager we'll notice the discrepancy between the
+  // animation generation numbers and update the layer indefinitely.
+  uint64_t animationGeneration =
+    RestyleManager::GetAnimationGenerationForFrame(aFrame);
+  aLayer->SetAnimationGeneration(animationGeneration);
+
+  EffectCompositor::ClearIsRunningOnCompositor(aFrame, aProperty);
+  nsTArray<RefPtr<dom::Animation>> compositorAnimations =
+    EffectCompositor::GetAnimationsForCompositor(aFrame, aProperty);
+  if (compositorAnimations.IsEmpty()) {
+    return;
+  }
+
+  // If the frame is not prerendered, bail out.
+  // Do this check only during layer construction; during updating the
+  // caller is required to check it appropriately.
+  if (aItem && !aItem->CanUseAsyncAnimations(aBuilder)) {
+    // EffectCompositor needs to know that we refused to run this animation
+    // asynchronously so that it will not throttle the main thread
+    // animation.
+    aFrame->Properties().Set(nsIFrame::RefusedAsyncAnimationProperty(), true);
+
+    // We need to schedule another refresh driver run so that EffectCompositor
+    // gets a chance to unthrottle the animation.
+    aFrame->SchedulePaint();
+    return;
+  }
+
+  AnimationData data;
+  if (aProperty == eCSSProperty_transform) {
+    // XXX Performance here isn't ideal for SVG. We'd prefer to avoid resolving
+    // the dimensions of refBox. That said, we only get here if there are CSS
+    // animations or transitions on this element, and that is likely to be a
+    // lot rarer than transforms on SVG (the frequency of which drives the need
+    // for TransformReferenceBox).
+    TransformReferenceBox refBox(aFrame);
+    nsRect bounds(0, 0, refBox.Width(), refBox.Height());
+    // all data passed directly to the compositor should be in dev pixels
+    int32_t devPixelsToAppUnits = aFrame->PresContext()->AppUnitsPerDevPixel();
+    float scale = devPixelsToAppUnits;
+    Point3D offsetToTransformOrigin =
+      nsDisplayTransform::GetDeltaToTransformOrigin(aFrame, scale, &bounds);
+    nsPoint origin;
+    if (aItem) {
+      // This branch is for display items to leverage the cache of
+      // nsDisplayListBuilder.
+      origin = aItem->ToReferenceFrame();
+    } else {
+      // This branch is running for restyling.
+      // Animations are animated at the coordination of the reference
+      // frame outside, not the given frame itself.  The given frame
+      // is also reference frame too, so the parent's reference frame
+      // are used.
+      nsIFrame* referenceFrame =
+        nsLayoutUtils::GetReferenceFrame(nsLayoutUtils::GetCrossDocParentFrame(aFrame));
+      origin = aFrame->GetOffsetToCrossDoc(referenceFrame);
+    }
+
+    data = TransformData(origin, offsetToTransformOrigin,
+                         bounds, devPixelsToAppUnits);
+  } else if (aProperty == eCSSProperty_opacity) {
+    data = null_t();
+  }
+
+  AddAnimationsForProperty(aFrame, aProperty, compositorAnimations,
+                           aLayer, data, pending);
+}
+
+nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
+    nsDisplayListBuilderMode aMode, bool aBuildCaret)
+    : mReferenceFrame(aReferenceFrame),
+      mIgnoreScrollFrame(nullptr),
+      mLayerEventRegions(nullptr),
+      mCurrentTableItem(nullptr),
+      mCurrentFrame(aReferenceFrame),
+      mCurrentReferenceFrame(aReferenceFrame),
+      mCurrentAGR(&mRootAGR),
+      mRootAGR(aReferenceFrame, nullptr),
+      mUsedAGRBudget(0),
+      mDirtyRect(-1,-1,-1,-1),
+      mGlassDisplayItem(nullptr),
+      mScrollInfoItemsForHoisting(nullptr),
+      mMode(aMode),
+      mCurrentScrollParentId(FrameMetrics::NULL_SCROLL_ID),
+      mCurrentScrollbarTarget(FrameMetrics::NULL_SCROLL_ID),
+      mCurrentScrollbarFlags(0),
+      mPerspectiveItemIndex(0),
+      mSVGEffectsBuildingDepth(0),
+      mContainsBlendMode(false),
+      mIsBuildingScrollbar(false),
+      mCurrentScrollbarWillHaveLayer(false),
+      mBuildCaret(aBuildCaret),
+      mIgnoreSuppression(false),
+      mIsAtRootOfPseudoStackingContext(false),
+      mIncludeAllOutOfFlows(false),
+      mDescendIntoSubdocuments(true),
+      mSelectedFramesOnly(false),
+      mAccurateVisibleRegions(false),
+      mAllowMergingAndFlattening(true),
+      mWillComputePluginGeometry(false),
+      mInTransform(false),
+      mIsInChromePresContext(false),
+      mSyncDecodeImages(false),
+      mIsPaintingToWindow(false),
+      mIsCompositingCheap(false),
+      mContainsPluginItem(false),
+      mAncestorHasApzAwareEventHandler(false),
+      mHaveScrollableDisplayPort(false),
+      mWindowDraggingAllowed(false),
+      mIsBuildingForPopup(nsLayoutUtils::IsPopup(aReferenceFrame)),
+      mForceLayerForScrollParent(false),
+      mAsyncPanZoomEnabled(nsLayoutUtils::AsyncPanZoomEnabled(aReferenceFrame)),
+      mBuildingInvisibleItems(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayListBuilder);
+  PL_InitArenaPool(&mPool, "displayListArena", 4096,
+                   std::max(NS_ALIGNMENT_OF(void*),NS_ALIGNMENT_OF(double))-1);
+
+  nsPresContext* pc = aReferenceFrame->PresContext();
+  nsIPresShell *shell = pc->PresShell();
+  if (pc->IsRenderingOnlySelection()) {
+    nsCOMPtr<nsISelectionController> selcon(do_QueryInterface(shell));
+    if (selcon) {
+      selcon->GetSelection(nsISelectionController::SELECTION_NORMAL,
+                           getter_AddRefs(mBoundingSelection));
+    }
+  }
+
+  mFrameToAnimatedGeometryRootMap.Put(aReferenceFrame, &mRootAGR);
+
+  nsCSSRendering::BeginFrameTreesLocked();
+  static_assert(nsDisplayItem::TYPE_MAX < (1 << nsDisplayItem::TYPE_BITS),
+                "Check nsDisplayItem::TYPE_MAX should not overflow");
+}
+
+static void MarkFrameForDisplay(nsIFrame* aFrame, nsIFrame* aStopAtFrame) {
+  for (nsIFrame* f = aFrame; f;
+       f = nsLayoutUtils::GetParentOrPlaceholderFor(f)) {
+    if (f->GetStateBits() & NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO)
+      return;
+    f->AddStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO);
+    if (f == aStopAtFrame) {
+      // we've reached a frame that we know will be painted, so we can stop.
+      break;
+    }
+  }
+}
+
+bool nsDisplayListBuilder::NeedToForceTransparentSurfaceForItem(nsDisplayItem* aItem)
+{
+  return aItem == mGlassDisplayItem || aItem->ClearsBackground();
+}
+
+AnimatedGeometryRoot*
+nsDisplayListBuilder::WrapAGRForFrame(nsIFrame* aAnimatedGeometryRoot,
+                                      AnimatedGeometryRoot* aParent /* = nullptr */)
+{
+  MOZ_ASSERT(IsAnimatedGeometryRoot(aAnimatedGeometryRoot));
+
+  AnimatedGeometryRoot* result = nullptr;
+  if (!mFrameToAnimatedGeometryRootMap.Get(aAnimatedGeometryRoot, &result)) {
+    MOZ_ASSERT(nsLayoutUtils::IsAncestorFrameCrossDoc(RootReferenceFrame(), aAnimatedGeometryRoot));
+    AnimatedGeometryRoot* parent = aParent;
+    if (!parent) {
+      nsIFrame* parentFrame = nsLayoutUtils::GetCrossDocParentFrame(aAnimatedGeometryRoot);
+      if (parentFrame) {
+        nsIFrame* parentAGRFrame = FindAnimatedGeometryRootFrameFor(parentFrame);
+        parent = WrapAGRForFrame(parentAGRFrame);
+      }
+    }
+    result = new (this) AnimatedGeometryRoot(aAnimatedGeometryRoot, parent);
+    mFrameToAnimatedGeometryRootMap.Put(aAnimatedGeometryRoot, result);
+  }
+  MOZ_ASSERT(!aParent || result->mParentAGR == aParent);
+  return result;
+}
+
+AnimatedGeometryRoot*
+nsDisplayListBuilder::FindAnimatedGeometryRootFor(nsIFrame* aFrame)
+{
+  if (!IsPaintingToWindow()) {
+    return &mRootAGR;
+  }
+  if (aFrame == mCurrentFrame) {
+    return mCurrentAGR;
+  }
+  AnimatedGeometryRoot* result = nullptr;
+  if (mFrameToAnimatedGeometryRootMap.Get(aFrame, &result)) {
+    return result;
+  }
+
+  nsIFrame* agrFrame = FindAnimatedGeometryRootFrameFor(aFrame);
+  result = WrapAGRForFrame(agrFrame);
+  mFrameToAnimatedGeometryRootMap.Put(aFrame, result);
+  return result;
+}
+
+AnimatedGeometryRoot*
+nsDisplayListBuilder::FindAnimatedGeometryRootFor(nsDisplayItem* aItem)
+{
+  if (aItem->ShouldFixToViewport(this)) {
+    // Make its active scrolled root be the active scrolled root of
+    // the enclosing viewport, since it shouldn't be scrolled by scrolled
+    // frames in its document. InvalidateFixedBackgroundFramesFromList in
+    // nsGfxScrollFrame will not repaint this item when scrolling occurs.
+    nsIFrame* viewportFrame =
+      nsLayoutUtils::GetClosestFrameOfType(aItem->Frame(), nsGkAtoms::viewportFrame, RootReferenceFrame());
+    if (viewportFrame) {
+      return FindAnimatedGeometryRootFor(viewportFrame);
+    }
+  }
+  return FindAnimatedGeometryRootFor(aItem->Frame());
+}
+
+
+void nsDisplayListBuilder::MarkOutOfFlowFrameForDisplay(nsIFrame* aDirtyFrame,
+                                                        nsIFrame* aFrame,
+                                                        const nsRect& aDirtyRect)
+{
+  nsRect dirtyRectRelativeToDirtyFrame = aDirtyRect;
+  if (nsLayoutUtils::IsFixedPosFrameInDisplayPort(aFrame) &&
+      IsPaintingToWindow()) {
+    NS_ASSERTION(aDirtyFrame == aFrame->GetParent(), "Dirty frame should be viewport frame");
+    // position: fixed items are reflowed into and only drawn inside the
+    // viewport, or the scroll position clamping scrollport size, if one is
+    // set.
+    nsIPresShell* ps = aFrame->PresContext()->PresShell();
+    dirtyRectRelativeToDirtyFrame.MoveTo(0, 0);
+    if (ps->IsScrollPositionClampingScrollPortSizeSet()) {
+      dirtyRectRelativeToDirtyFrame.SizeTo(ps->GetScrollPositionClampingScrollPortSize());
+    } else {
+      dirtyRectRelativeToDirtyFrame.SizeTo(aDirtyFrame->GetSize());
+    }
+  }
+  nsRect dirty = dirtyRectRelativeToDirtyFrame - aFrame->GetOffsetTo(aDirtyFrame);
+  nsRect overflowRect = aFrame->GetVisualOverflowRect();
+
+  if (aFrame->IsTransformed() &&
+      EffectCompositor::HasAnimationsForCompositor(aFrame,
+                                                   eCSSProperty_transform)) {
+   /**
+    * Add a fuzz factor to the overflow rectangle so that elements only just
+    * out of view are pulled into the display list, so they can be
+    * prerendered if necessary.
+    */
+    overflowRect.Inflate(nsPresContext::CSSPixelsToAppUnits(32));
+  }
+
+  if (!dirty.IntersectRect(dirty, overflowRect) &&
+      !(aFrame->GetStateBits() & NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO)) {
+    return;
+  }
+
+  const DisplayItemClip* oldClip = mClipState.GetClipForContainingBlockDescendants();
+  const DisplayItemScrollClip* sc = mClipState.GetCurrentInnermostScrollClip();
+  OutOfFlowDisplayData* data = new OutOfFlowDisplayData(oldClip, sc, dirty);
+  aFrame->Properties().Set(nsDisplayListBuilder::OutOfFlowDisplayDataProperty(), data);
+
+  MarkFrameForDisplay(aFrame, aDirtyFrame);
+}
+
+static void UnmarkFrameForDisplay(nsIFrame* aFrame) {
+  nsPresContext* presContext = aFrame->PresContext();
+  presContext->PropertyTable()->
+    Delete(aFrame, nsDisplayListBuilder::OutOfFlowDisplayDataProperty());
+
+  for (nsIFrame* f = aFrame; f;
+       f = nsLayoutUtils::GetParentOrPlaceholderFor(f)) {
+    if (!(f->GetStateBits() & NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO))
+      return;
+    f->RemoveStateBits(NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO);
+  }
+}
+
+nsDisplayListBuilder::~nsDisplayListBuilder() {
+  NS_ASSERTION(mFramesMarkedForDisplay.Length() == 0,
+               "All frames should have been unmarked");
+  NS_ASSERTION(mPresShellStates.Length() == 0,
+               "All presshells should have been exited");
+  NS_ASSERTION(!mCurrentTableItem, "No table item should be active");
+
+  nsCSSRendering::EndFrameTreesLocked();
+
+  for (DisplayItemClip* c : mDisplayItemClipsToDestroy) {
+    c->DisplayItemClip::~DisplayItemClip();
+  }
+  for (DisplayItemScrollClip* c : mScrollClipsToDestroy) {
+    c->DisplayItemScrollClip::~DisplayItemScrollClip();
+  }
+
+  PL_FinishArenaPool(&mPool);
+  MOZ_COUNT_DTOR(nsDisplayListBuilder);
+}
+
+uint32_t
+nsDisplayListBuilder::GetBackgroundPaintFlags() {
+  uint32_t flags = 0;
+  if (mSyncDecodeImages) {
+    flags |= nsCSSRendering::PAINTBG_SYNC_DECODE_IMAGES;
+  }
+  if (mIsPaintingToWindow) {
+    flags |= nsCSSRendering::PAINTBG_TO_WINDOW;
+  }
+  return flags;
+}
+
+void
+nsDisplayListBuilder::SubtractFromVisibleRegion(nsRegion* aVisibleRegion,
+                                                const nsRegion& aRegion)
+{
+  if (aRegion.IsEmpty())
+    return;
+
+  nsRegion tmp;
+  tmp.Sub(*aVisibleRegion, aRegion);
+  // Don't let *aVisibleRegion get too complex, but don't let it fluff out
+  // to its bounds either, which can be very bad (see bug 516740).
+  // Do let aVisibleRegion get more complex if by doing so we reduce its
+  // area by at least half.
+  if (GetAccurateVisibleRegions() || tmp.GetNumRects() <= 15 ||
+      tmp.Area() <= aVisibleRegion->Area()/2) {
+    *aVisibleRegion = tmp;
+  }
+}
+
+nsCaret *
+nsDisplayListBuilder::GetCaret() {
+  RefPtr<nsCaret> caret = CurrentPresShellState()->mPresShell->GetCaret();
+  return caret;
+}
+
+void
+nsDisplayListBuilder::EnterPresShell(nsIFrame* aReferenceFrame,
+                                     bool aPointerEventsNoneDoc)
+{
+  PresShellState* state = mPresShellStates.AppendElement();
+  state->mPresShell = aReferenceFrame->PresContext()->PresShell();
+  state->mCaretFrame = nullptr;
+  state->mFirstFrameMarkedForDisplay = mFramesMarkedForDisplay.Length();
+
+  state->mPresShell->UpdateCanvasBackground();
+
+  if (mIsPaintingToWindow) {
+    mReferenceFrame->AddPaintedPresShell(state->mPresShell);
+
+    state->mPresShell->IncrementPaintCount();
+  }
+
+  bool buildCaret = mBuildCaret;
+  if (mIgnoreSuppression || !state->mPresShell->IsPaintingSuppressed()) {
+    state->mIsBackgroundOnly = false;
+  } else {
+    state->mIsBackgroundOnly = true;
+    buildCaret = false;
+  }
+
+  bool pointerEventsNone = aPointerEventsNoneDoc;
+  if (IsInSubdocument()) {
+    pointerEventsNone |= mPresShellStates[mPresShellStates.Length() - 2].mInsidePointerEventsNoneDoc;
+  }
+  state->mInsidePointerEventsNoneDoc = pointerEventsNone;
+
+  if (!buildCaret)
+    return;
+
+  RefPtr<nsCaret> caret = state->mPresShell->GetCaret();
+  state->mCaretFrame = caret->GetPaintGeometry(&state->mCaretRect);
+  if (state->mCaretFrame) {
+    mFramesMarkedForDisplay.AppendElement(state->mCaretFrame);
+    MarkFrameForDisplay(state->mCaretFrame, nullptr);
+  }
+
+  nsPresContext* pc = aReferenceFrame->PresContext();
+  nsCOMPtr<nsIDocShell> docShell = pc->GetDocShell();
+  if (docShell) {
+    docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+  }
+  mIsInChromePresContext = pc->IsChrome();
+}
+
+// A non-blank paint is a paint that does not just contain the canvas background.
+static bool
+DisplayListIsNonBlank(nsDisplayList* aList)
+{
+  for (nsDisplayItem* i = aList->GetBottom(); i != nullptr; i = i->GetAbove()) {
+    switch (i->GetType()) {
+      case nsDisplayItem::TYPE_LAYER_EVENT_REGIONS:
+      case nsDisplayItem::TYPE_CANVAS_BACKGROUND_COLOR:
+      case nsDisplayItem::TYPE_CANVAS_BACKGROUND_IMAGE:
+        continue;
+      case nsDisplayItem::TYPE_SOLID_COLOR:
+      case nsDisplayItem::TYPE_BACKGROUND:
+      case nsDisplayItem::TYPE_BACKGROUND_COLOR:
+        if (i->Frame()->GetType() == nsGkAtoms::canvasFrame) {
+          continue;
+        }
+        return true;
+      default:
+        return true;
+    }
+  }
+  return false;
+}
+
+void
+nsDisplayListBuilder::LeavePresShell(nsIFrame* aReferenceFrame, nsDisplayList* aPaintedContents)
+{
+  NS_ASSERTION(CurrentPresShellState()->mPresShell ==
+      aReferenceFrame->PresContext()->PresShell(),
+      "Presshell mismatch");
+
+  if (mIsPaintingToWindow) {
+    nsPresContext* pc = aReferenceFrame->PresContext();
+    if (!pc->HadNonBlankPaint()) {
+      if (!CurrentPresShellState()->mIsBackgroundOnly &&
+          DisplayListIsNonBlank(aPaintedContents)) {
+        pc->NotifyNonBlankPaint();
+      }
+    }
+  }
+
+  ResetMarkedFramesForDisplayList();
+  mPresShellStates.SetLength(mPresShellStates.Length() - 1);
+
+  if (!mPresShellStates.IsEmpty()) {
+    nsPresContext* pc = CurrentPresContext();
+    nsCOMPtr<nsIDocShell> docShell = pc->GetDocShell();
+    if (docShell) {
+      docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+    }
+    mIsInChromePresContext = pc->IsChrome();
+  }
+}
+
+void
+nsDisplayListBuilder::ResetMarkedFramesForDisplayList()
+{
+  // Unmark and pop off the frames marked for display in this pres shell.
+  uint32_t firstFrameForShell = CurrentPresShellState()->mFirstFrameMarkedForDisplay;
+  for (uint32_t i = firstFrameForShell;
+       i < mFramesMarkedForDisplay.Length(); ++i) {
+    UnmarkFrameForDisplay(mFramesMarkedForDisplay[i]);
+  }
+  mFramesMarkedForDisplay.SetLength(firstFrameForShell);
+}
+
+void
+nsDisplayListBuilder::MarkFramesForDisplayList(nsIFrame* aDirtyFrame,
+                                               const nsFrameList& aFrames,
+                                               const nsRect& aDirtyRect) {
+  mFramesMarkedForDisplay.SetCapacity(mFramesMarkedForDisplay.Length() + aFrames.GetLength());
+  for (nsIFrame* e : aFrames) {
+    // Skip the AccessibleCaret frame when building no caret.
+    if (!IsBuildingCaret()) {
+      nsIContent* content = e->GetContent();
+      if (content && content->IsInNativeAnonymousSubtree() && content->IsElement()) {
+        auto classList = content->AsElement()->ClassList();
+        if (classList->Contains(NS_LITERAL_STRING("moz-accessiblecaret"))) {
+          continue;
+        }
+      }
+    }
+    mFramesMarkedForDisplay.AppendElement(e);
+    MarkOutOfFlowFrameForDisplay(aDirtyFrame, e, aDirtyRect);
+  }
+}
+
+/**
+ * Mark all preserve-3d children with
+ * NS_FRAME_FORCE_DISPLAY_LIST_DESCEND_INTO to make sure
+ * nsFrame::BuildDisplayListForChild() would visit them.  Also compute
+ * dirty rect for preserve-3d children.
+ *
+ * @param aDirtyFrame is the frame to mark children extending context.
+ */
+void
+nsDisplayListBuilder::MarkPreserve3DFramesForDisplayList(nsIFrame* aDirtyFrame)
+{
+  AutoTArray<nsIFrame::ChildList,4> childListArray;
+  aDirtyFrame->GetChildLists(&childListArray);
+  nsIFrame::ChildListArrayIterator lists(childListArray);
+  for (; !lists.IsDone(); lists.Next()) {
+    nsFrameList::Enumerator childFrames(lists.CurrentList());
+    for (; !childFrames.AtEnd(); childFrames.Next()) {
+      nsIFrame *child = childFrames.get();
+      if (child->Combines3DTransformWithAncestors()) {
+        mFramesMarkedForDisplay.AppendElement(child);
+        MarkFrameForDisplay(child, aDirtyFrame);
+      }
+    }
+  }
+}
+
+void*
+nsDisplayListBuilder::Allocate(size_t aSize)
+{
+  void *tmp;
+  PL_ARENA_ALLOCATE(tmp, &mPool, aSize);
+  if (!tmp) {
+    NS_ABORT_OOM(aSize);
+  }
+  return tmp;
+}
+
+const DisplayItemClip*
+nsDisplayListBuilder::AllocateDisplayItemClip(const DisplayItemClip& aOriginal)
+{
+  void* p = Allocate(sizeof(DisplayItemClip));
+  if (!aOriginal.GetRoundedRectCount()) {
+    memcpy(p, &aOriginal, sizeof(DisplayItemClip));
+    return static_cast<DisplayItemClip*>(p);
+  }
+
+  DisplayItemClip* c = new (KnownNotNull, p) DisplayItemClip(aOriginal);
+  mDisplayItemClipsToDestroy.AppendElement(c);
+  return c;
+}
+
+DisplayItemScrollClip*
+nsDisplayListBuilder::AllocateDisplayItemScrollClip(const DisplayItemScrollClip* aParent,
+                                                    nsIScrollableFrame* aScrollableFrame,
+                                                    const DisplayItemClip* aClip,
+                                                    bool aIsAsyncScrollable)
+{
+  void* p = Allocate(sizeof(DisplayItemScrollClip));
+  DisplayItemScrollClip* c =
+    new (KnownNotNull, p) DisplayItemScrollClip(aParent, aScrollableFrame,
+                                                aClip, aIsAsyncScrollable);
+  mScrollClipsToDestroy.AppendElement(c);
+  return c;
+}
+
+const nsIFrame*
+nsDisplayListBuilder::FindReferenceFrameFor(const nsIFrame *aFrame,
+                                            nsPoint* aOffset)
+{
+  if (aFrame == mCurrentFrame) {
+    if (aOffset) {
+      *aOffset = mCurrentOffsetToReferenceFrame;
+    }
+    return mCurrentReferenceFrame;
+  }
+  for (const nsIFrame* f = aFrame; f; f = nsLayoutUtils::GetCrossDocParentFrame(f))
+  {
+    if (f == mReferenceFrame || f->IsTransformed()) {
+      if (aOffset) {
+        *aOffset = aFrame->GetOffsetToCrossDoc(f);
+      }
+      return f;
+    }
+  }
+  if (aOffset) {
+    *aOffset = aFrame->GetOffsetToCrossDoc(mReferenceFrame);
+  }
+  return mReferenceFrame;
+}
+
+// Sticky frames are active if their nearest scrollable frame is also active.
+static bool
+IsStickyFrameActive(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, nsIFrame* aParent)
+{
+  MOZ_ASSERT(aFrame->StyleDisplay()->mPosition == NS_STYLE_POSITION_STICKY);
+
+  // Find the nearest scrollframe.
+  nsIFrame* cursor = aFrame;
+  nsIFrame* parent = aParent;
+  if (!parent) {
+    parent = nsLayoutUtils::GetCrossDocParentFrame(aFrame);
+  }
+  while (parent->GetType() != nsGkAtoms::scrollFrame) {
+    cursor = parent;
+    if ((parent = nsLayoutUtils::GetCrossDocParentFrame(cursor)) == nullptr) {
+      return false;
+    }
+  }
+
+  nsIScrollableFrame* sf = do_QueryFrame(parent);
+  return sf->IsScrollingActive(aBuilder) && sf->GetScrolledFrame() == cursor;
+}
+
+bool
+nsDisplayListBuilder::IsAnimatedGeometryRoot(nsIFrame* aFrame, nsIFrame** aParent)
+{
+  if (aFrame == mReferenceFrame) {
+    return true;
+  }
+  if (!IsPaintingToWindow()) {
+    if (aParent) {
+      *aParent = nsLayoutUtils::GetCrossDocParentFrame(aFrame);
+    }
+    return false;
+  }
+
+  if (nsLayoutUtils::IsPopup(aFrame))
+    return true;
+  if (ActiveLayerTracker::IsOffsetOrMarginStyleAnimated(aFrame)) {
+    const bool inBudget = AddToAGRBudget(aFrame);
+    if (inBudget) {
+      return true;
+    }
+  }
+  if (!aFrame->GetParent() &&
+      nsLayoutUtils::ViewportHasDisplayPort(aFrame->PresContext())) {
+    // Viewport frames in a display port need to be animated geometry roots
+    // for background-attachment:fixed elements.
+    return true;
+  }
+  if (aFrame->IsTransformed()) {
+    return true;
+  }
+
+  nsIFrame* parent = nsLayoutUtils::GetCrossDocParentFrame(aFrame);
+  if (!parent)
+    return true;
+
+  nsIAtom* parentType = parent->GetType();
+  // Treat the slider thumb as being as an active scrolled root when it wants
+  // its own layer so that it can move without repainting.
+  if (parentType == nsGkAtoms::sliderFrame && nsLayoutUtils::IsScrollbarThumbLayerized(aFrame)) {
+    return true;
+  }
+
+  if (aFrame->StyleDisplay()->mPosition == NS_STYLE_POSITION_STICKY &&
+      IsStickyFrameActive(this, aFrame, parent))
+  {
+    return true;
+  }
+
+  if (parentType == nsGkAtoms::scrollFrame || parentType == nsGkAtoms::listControlFrame) {
+    nsIScrollableFrame* sf = do_QueryFrame(parent);
+    if (sf->IsScrollingActive(this) && sf->GetScrolledFrame() == aFrame) {
+      return true;
+    }
+  }
+
+  // Fixed-pos frames are parented by the viewport frame, which has no parent.
+  if (nsLayoutUtils::IsFixedPosFrameInDisplayPort(aFrame)) {
+    return true;
+  }
+
+  if (aParent) {
+    *aParent = parent;
+  }
+  return false;
+}
+
+nsIFrame*
+nsDisplayListBuilder::FindAnimatedGeometryRootFrameFor(nsIFrame* aFrame)
+{
+  MOZ_ASSERT(nsLayoutUtils::IsAncestorFrameCrossDoc(RootReferenceFrame(), aFrame));
+  nsIFrame* cursor = aFrame;
+  while (cursor != RootReferenceFrame()) {
+    nsIFrame* next;
+    if (IsAnimatedGeometryRoot(cursor, &next))
+      return cursor;
+    cursor = next;
+  }
+  return cursor;
+}
+
+void
+nsDisplayListBuilder::RecomputeCurrentAnimatedGeometryRoot()
+{
+  if (*mCurrentAGR != mCurrentFrame &&
+      IsAnimatedGeometryRoot(const_cast<nsIFrame*>(mCurrentFrame))) {
+    AnimatedGeometryRoot* oldAGR = mCurrentAGR;
+    mCurrentAGR = WrapAGRForFrame(const_cast<nsIFrame*>(mCurrentFrame), mCurrentAGR);
+
+    // Iterate the AGR cache and look for any objects that reference the old AGR and check
+    // to see if they need to be updated. AGRs can be in the cache multiple times, so we may
+    // end up doing the work multiple times for AGRs that don't change.
+    for (auto iter = mFrameToAnimatedGeometryRootMap.Iter(); !iter.Done(); iter.Next()) {
+      AnimatedGeometryRoot* cached = iter.UserData();
+      if (cached->mParentAGR == oldAGR && cached != mCurrentAGR) {
+        // It's possible that this cached AGR struct that has the old AGR as a parent
+        // should instead have mCurrentFrame has a parent.
+        nsIFrame* parent = FindAnimatedGeometryRootFrameFor(*cached);
+        MOZ_ASSERT(parent == mCurrentFrame || parent == *oldAGR);
+        if (parent == mCurrentFrame) {
+          cached->mParentAGR = mCurrentAGR;
+        }
+      }
+    }
+  }
+}
+
+void
+nsDisplayListBuilder::AdjustWindowDraggingRegion(nsIFrame* aFrame)
+{
+  if (!mWindowDraggingAllowed || !IsForPainting()) {
+    return;
+  }
+
+  const nsStyleUIReset* styleUI = aFrame->StyleUIReset();
+  if (styleUI->mWindowDragging == StyleWindowDragging::Default) {
+    // This frame has the default value and doesn't influence the window
+    // dragging region.
+    return;
+  }
+
+  LayoutDeviceToLayoutDeviceMatrix4x4 referenceFrameToRootReferenceFrame;
+
+  // The const_cast is for nsLayoutUtils::GetTransformToAncestor.
+  nsIFrame* referenceFrame = const_cast<nsIFrame*>(FindReferenceFrameFor(aFrame));
+
+  if (IsInTransform()) {
+    // Only support 2d rectilinear transforms. Transform support is needed for
+    // the horizontal flip transform that's applied to the urlbar textbox in
+    // RTL mode - it should be able to exclude itself from the draggable region.
+    referenceFrameToRootReferenceFrame =
+      ViewAs<LayoutDeviceToLayoutDeviceMatrix4x4>(
+          nsLayoutUtils::GetTransformToAncestor(referenceFrame, mReferenceFrame));
+    Matrix referenceFrameToRootReferenceFrame2d;
+    if (!referenceFrameToRootReferenceFrame.Is2D(&referenceFrameToRootReferenceFrame2d) ||
+        !referenceFrameToRootReferenceFrame2d.IsRectilinear()) {
+      return;
+    }
+  } else {
+    MOZ_ASSERT(referenceFrame == mReferenceFrame,
+               "referenceFrameToRootReferenceFrame needs to be adjusted");
+  }
+
+  // We do some basic visibility checking on the frame's border box here.
+  // We intersect it both with the current dirty rect and with the current
+  // clip. Either one is just a conservative approximation on its own, but
+  // their intersection luckily works well enough for our purposes, so that
+  // we don't have to do full-blown visibility computations.
+  // The most important case we need to handle is the scrolled-off tab:
+  // If the tab bar overflows, tab parts that are clipped by the scrollbox
+  // should not be allowed to interfere with the window dragging region. Using
+  // just the current DisplayItemClip is not enough to cover this case
+  // completely because clips are reset while building stacking context
+  // contents, so for example we'd fail to clip frames that have a clip path
+  // applied to them. But the current dirty rect doesn't get reset in that
+  // case, so we use it to make this case work.
+  nsRect borderBox = aFrame->GetRectRelativeToSelf().Intersect(mDirtyRect);
+  borderBox += ToReferenceFrame(aFrame);
+  const DisplayItemClip* clip = ClipState().GetCurrentCombinedClip(this);
+  if (clip) {
+    borderBox = clip->ApplyNonRoundedIntersection(borderBox);
+  }
+  if (!borderBox.IsEmpty()) {
+    LayoutDeviceRect devPixelBorderBox =
+      LayoutDevicePixel::FromAppUnits(borderBox, aFrame->PresContext()->AppUnitsPerDevPixel());
+    LayoutDeviceRect transformedDevPixelBorderBox =
+      TransformBy(referenceFrameToRootReferenceFrame, devPixelBorderBox);
+    transformedDevPixelBorderBox.Round();
+    LayoutDeviceIntRect transformedDevPixelBorderBoxInt;
+    if (transformedDevPixelBorderBox.ToIntRect(&transformedDevPixelBorderBoxInt)) {
+      if (styleUI->mWindowDragging == StyleWindowDragging::Drag) {
+        mWindowDraggingRegion.OrWith(transformedDevPixelBorderBoxInt);
+      } else {
+        mWindowNoDraggingRegion.OrWith(transformedDevPixelBorderBoxInt);
+      }
+    }
+  }
+}
+
+LayoutDeviceIntRegion
+nsDisplayListBuilder::GetWindowDraggingRegion() const
+{
+  LayoutDeviceIntRegion result;
+  result.Sub(mWindowDraggingRegion, mWindowNoDraggingRegion);;
+  return result;
+}
+
+const uint32_t gWillChangeAreaMultiplier = 3;
+static uint32_t GetLayerizationCost(const nsSize& aSize) {
+  // There's significant overhead for each layer created from Gecko
+  // (IPC+Shared Objects) and from the backend (like an OpenGL texture).
+  // Therefore we set a minimum cost threshold of a 64x64 area.
+  int minBudgetCost = 64 * 64;
+
+  uint32_t budgetCost =
+    std::max(minBudgetCost,
+      nsPresContext::AppUnitsToIntCSSPixels(aSize.width) *
+      nsPresContext::AppUnitsToIntCSSPixels(aSize.height));
+
+  return budgetCost;
+}
+
+bool
+nsDisplayListBuilder::AddToWillChangeBudget(nsIFrame* aFrame,
+                                            const nsSize& aSize) {
+  if (mWillChangeBudgetSet.Contains(aFrame)) {
+    return true; // Already accounted
+  }
+
+  nsPresContext* key = aFrame->PresContext();
+  if (!mWillChangeBudget.Contains(key)) {
+    mWillChangeBudget.Put(key, DocumentWillChangeBudget());
+  }
+
+  DocumentWillChangeBudget budget;
+  mWillChangeBudget.Get(key, &budget);
+
+  nsRect area = aFrame->PresContext()->GetVisibleArea();
+  uint32_t budgetLimit = nsPresContext::AppUnitsToIntCSSPixels(area.width) *
+    nsPresContext::AppUnitsToIntCSSPixels(area.height);
+
+  uint32_t cost = GetLayerizationCost(aSize);
+  bool onBudget = (budget.mBudget + cost) /
+                    gWillChangeAreaMultiplier < budgetLimit;
+
+  if (onBudget) {
+    budget.mBudget += cost;
+    mWillChangeBudget.Put(key, budget);
+    mWillChangeBudgetSet.PutEntry(aFrame);
+  }
+
+  return onBudget;
+}
+
+bool
+nsDisplayListBuilder::IsInWillChangeBudget(nsIFrame* aFrame,
+                                           const nsSize& aSize) {
+  bool onBudget = AddToWillChangeBudget(aFrame, aSize);
+
+  if (!onBudget) {
+    nsString usageStr;
+    usageStr.AppendInt(GetLayerizationCost(aSize));
+
+    nsString multiplierStr;
+    multiplierStr.AppendInt(gWillChangeAreaMultiplier);
+
+    nsString limitStr;
+    nsRect area = aFrame->PresContext()->GetVisibleArea();
+    uint32_t budgetLimit = nsPresContext::AppUnitsToIntCSSPixels(area.width) *
+      nsPresContext::AppUnitsToIntCSSPixels(area.height);
+    limitStr.AppendInt(budgetLimit);
+
+    const char16_t* params[] = { multiplierStr.get(), limitStr.get() };
+    aFrame->PresContext()->Document()->WarnOnceAbout(
+      nsIDocument::eIgnoringWillChangeOverBudget, false,
+      params, ArrayLength(params));
+  }
+  return onBudget;
+}
+
+#ifdef MOZ_GFX_OPTIMIZE_MOBILE
+const float gAGRBudgetAreaMultiplier = 0.3;
+#else
+const float gAGRBudgetAreaMultiplier = 3.0;
+#endif
+
+bool
+nsDisplayListBuilder::AddToAGRBudget(nsIFrame* aFrame)
+{
+  if (mAGRBudgetSet.Contains(aFrame)) {
+    return true;
+  }
+
+  const nsPresContext* presContext = aFrame->PresContext()->GetRootPresContext();
+  if (!presContext) {
+    return false;
+  }
+
+  const nsRect area = presContext->GetVisibleArea();
+  const uint32_t budgetLimit = gAGRBudgetAreaMultiplier *
+    nsPresContext::AppUnitsToIntCSSPixels(area.width) *
+    nsPresContext::AppUnitsToIntCSSPixels(area.height);
+
+  const uint32_t cost = GetLayerizationCost(aFrame->GetSize());
+  const bool onBudget = mUsedAGRBudget + cost < budgetLimit;
+
+  if (onBudget) {
+    mUsedAGRBudget += cost;
+    mAGRBudgetSet.PutEntry(aFrame);
+  }
+
+  return onBudget;
+}
+
+void
+nsDisplayListBuilder::EnterSVGEffectsContents(nsDisplayList* aHoistedItemsStorage)
+{
+  MOZ_ASSERT(mSVGEffectsBuildingDepth >= 0);
+  MOZ_ASSERT(aHoistedItemsStorage);
+  if (mSVGEffectsBuildingDepth == 0) {
+    MOZ_ASSERT(!mScrollInfoItemsForHoisting);
+    mScrollInfoItemsForHoisting = aHoistedItemsStorage;
+  }
+  mSVGEffectsBuildingDepth++;
+}
+
+void
+nsDisplayListBuilder::ExitSVGEffectsContents()
+{
+  mSVGEffectsBuildingDepth--;
+  MOZ_ASSERT(mSVGEffectsBuildingDepth >= 0);
+  MOZ_ASSERT(mScrollInfoItemsForHoisting);
+  if (mSVGEffectsBuildingDepth == 0) {
+    mScrollInfoItemsForHoisting = nullptr;
+  }
+}
+
+void
+nsDisplayListBuilder::AppendNewScrollInfoItemForHoisting(nsDisplayScrollInfoLayer* aScrollInfoItem)
+{
+  MOZ_ASSERT(ShouldBuildScrollInfoItemsForHoisting());
+  MOZ_ASSERT(mScrollInfoItemsForHoisting);
+  mScrollInfoItemsForHoisting->AppendNewToTop(aScrollInfoItem);
+}
+
+bool
+nsDisplayListBuilder::IsBuildingLayerEventRegions()
+{
+  if (IsPaintingToWindow()) {
+    // Note: this function and LayerEventRegionsEnabled are the only places
+    // that get to query LayoutEventRegionsEnabled 'directly' - other code
+    // should call this function.
+    return gfxPrefs::LayoutEventRegionsEnabledDoNotUseDirectly() ||
+           mAsyncPanZoomEnabled;
+  }
+  return false;
+}
+
+/* static */ bool
+nsDisplayListBuilder::LayerEventRegionsEnabled()
+{
+  // Note: this function and IsBuildingLayerEventRegions are the only places
+  // that get to query LayoutEventRegionsEnabled 'directly' - other code
+  // should call this function.
+  return gfxPrefs::LayoutEventRegionsEnabledDoNotUseDirectly() ||
+         gfxPlatform::AsyncPanZoomEnabled();
+}
+
+void nsDisplayListSet::MoveTo(const nsDisplayListSet& aDestination) const
+{
+  aDestination.BorderBackground()->AppendToTop(BorderBackground());
+  aDestination.BlockBorderBackgrounds()->AppendToTop(BlockBorderBackgrounds());
+  aDestination.Floats()->AppendToTop(Floats());
+  aDestination.Content()->AppendToTop(Content());
+  aDestination.PositionedDescendants()->AppendToTop(PositionedDescendants());
+  aDestination.Outlines()->AppendToTop(Outlines());
+}
+
+static void
+MoveListTo(nsDisplayList* aList, nsTArray<nsDisplayItem*>* aElements) {
+  nsDisplayItem* item;
+  while ((item = aList->RemoveBottom()) != nullptr) {
+    aElements->AppendElement(item);
+  }
+}
+
+nsRect
+nsDisplayList::GetBounds(nsDisplayListBuilder* aBuilder) const {
+  nsRect bounds;
+  for (nsDisplayItem* i = GetBottom(); i != nullptr; i = i->GetAbove()) {
+    bounds.UnionRect(bounds, i->GetClippedBounds(aBuilder));
+  }
+  return bounds;
+}
+
+nsRect
+nsDisplayList::GetScrollClippedBoundsUpTo(nsDisplayListBuilder* aBuilder,
+                                          const DisplayItemScrollClip* aIncludeScrollClipsUpTo) const {
+  nsRect bounds;
+  for (nsDisplayItem* i = GetBottom(); i != nullptr; i = i->GetAbove()) {
+    nsRect r = i->GetClippedBounds(aBuilder);
+    if (r.IsEmpty()) {
+      continue;
+    }
+    for (auto* sc = i->ScrollClip(); sc && sc != aIncludeScrollClipsUpTo; sc = sc->mParent) {
+      if (sc->mClip && sc->mClip->HasClip()) {
+        if (sc->mIsAsyncScrollable) {
+          // Assume the item can move anywhere in the scroll clip's clip rect.
+          r = sc->mClip->GetClipRect();
+        } else {
+          r = sc->mClip->ApplyNonRoundedIntersection(r);
+        }
+      }
+    }
+    bounds.UnionRect(bounds, r);
+  }
+  return bounds;
+}
+
+nsRect
+nsDisplayList::GetVisibleRect() const {
+  nsRect result;
+  for (nsDisplayItem* i = GetBottom(); i != nullptr; i = i->GetAbove()) {
+    result.UnionRect(result, i->GetVisibleRect());
+  }
+  return result;
+}
+
+bool
+nsDisplayList::ComputeVisibilityForRoot(nsDisplayListBuilder* aBuilder,
+                                        nsRegion* aVisibleRegion) {
+  PROFILER_LABEL("nsDisplayList", "ComputeVisibilityForRoot",
+    js::ProfileEntry::Category::GRAPHICS);
+
+  nsRegion r;
+  r.And(*aVisibleRegion, GetBounds(aBuilder));
+  return ComputeVisibilityForSublist(aBuilder, aVisibleRegion, r.GetBounds());
+}
+
+static nsRegion
+TreatAsOpaque(nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder)
+{
+  bool snap;
+  nsRegion opaque = aItem->GetOpaqueRegion(aBuilder, &snap);
+  if (aBuilder->IsForPluginGeometry() &&
+      aItem->GetType() != nsDisplayItem::TYPE_LAYER_EVENT_REGIONS)
+  {
+    // Treat all leaf chrome items as opaque, unless their frames are opacity:0.
+    // Since opacity:0 frames generate an nsDisplayOpacity, that item will
+    // not be treated as opaque here, so opacity:0 chrome content will be
+    // effectively ignored, as it should be.
+    // We treat leaf chrome items as opaque to ensure that they cover
+    // content plugins, for security reasons.
+    // Non-leaf chrome items don't render contents of their own so shouldn't
+    // be treated as opaque (and their bounds is just the union of their
+    // children, which might be a large area their contents don't really cover).
+    nsIFrame* f = aItem->Frame();
+    if (f->PresContext()->IsChrome() && !aItem->GetChildren() &&
+        f->StyleEffects()->mOpacity != 0.0) {
+      opaque = aItem->GetBounds(aBuilder, &snap);
+    }
+  }
+  if (opaque.IsEmpty()) {
+    return opaque;
+  }
+  nsRegion opaqueClipped;
+  for (auto iter = opaque.RectIter(); !iter.Done(); iter.Next()) {
+    opaqueClipped.Or(opaqueClipped,
+                     aItem->GetClip().ApproximateIntersectInward(iter.Get()));
+  }
+  return opaqueClipped;
+}
+
+bool
+nsDisplayList::ComputeVisibilityForSublist(nsDisplayListBuilder* aBuilder,
+                                           nsRegion* aVisibleRegion,
+                                           const nsRect& aListVisibleBounds)
+{
+#ifdef DEBUG
+  nsRegion r;
+  r.And(*aVisibleRegion, GetBounds(aBuilder));
+  NS_ASSERTION(r.GetBounds().IsEqualInterior(aListVisibleBounds),
+               "bad aListVisibleBounds");
+#endif
+
+  bool anyVisible = false;
+
+  AutoTArray<nsDisplayItem*, 512> elements;
+  MoveListTo(this, &elements);
+
+  for (int32_t i = elements.Length() - 1; i >= 0; --i) {
+    nsDisplayItem* item = elements[i];
+
+    if (item->mForceNotVisible && !item->GetSameCoordinateSystemChildren()) {
+      NS_ASSERTION(item->mVisibleRect.IsEmpty(),
+        "invisible items should have empty vis rect");
+    } else {
+      nsRect bounds = item->GetClippedBounds(aBuilder);
+
+      nsRegion itemVisible;
+      itemVisible.And(*aVisibleRegion, bounds);
+      item->mVisibleRect = itemVisible.GetBounds();
+    }
+
+    if (item->ComputeVisibility(aBuilder, aVisibleRegion)) {
+      anyVisible = true;
+
+      nsRegion opaque = TreatAsOpaque(item, aBuilder);
+      // Subtract opaque item from the visible region
+      aBuilder->SubtractFromVisibleRegion(aVisibleRegion, opaque);
+    }
+    AppendToBottom(item);
+  }
+
+  mIsOpaque = !aVisibleRegion->Intersects(aListVisibleBounds);
+  return anyVisible;
+}
+
+static bool
+TriggerPendingAnimationsOnSubDocuments(nsIDocument* aDocument, void* aReadyTime)
+{
+  PendingAnimationTracker* tracker = aDocument->GetPendingAnimationTracker();
+  if (tracker) {
+    nsIPresShell* shell = aDocument->GetShell();
+    // If paint-suppression is in effect then we haven't finished painting
+    // this document yet so we shouldn't start animations
+    if (!shell || !shell->IsPaintingSuppressed()) {
+      const TimeStamp& readyTime = *static_cast<TimeStamp*>(aReadyTime);
+      tracker->TriggerPendingAnimationsOnNextTick(readyTime);
+    }
+  }
+  aDocument->EnumerateSubDocuments(TriggerPendingAnimationsOnSubDocuments,
+                                   aReadyTime);
+  return true;
+}
+
+static void
+TriggerPendingAnimations(nsIDocument* aDocument,
+                       const TimeStamp& aReadyTime) {
+  MOZ_ASSERT(!aReadyTime.IsNull(),
+             "Animation ready time is not set. Perhaps we're using a layer"
+             " manager that doesn't update it");
+  TriggerPendingAnimationsOnSubDocuments(aDocument,
+                                         const_cast<TimeStamp*>(&aReadyTime));
+}
+
+LayerManager*
+nsDisplayListBuilder::GetWidgetLayerManager(nsView** aView)
+{
+  nsView* view = RootReferenceFrame()->GetView();
+  if (aView) {
+    *aView = view;
+  }
+  if (RootReferenceFrame() != nsLayoutUtils::GetDisplayRootFrame(RootReferenceFrame())) {
+    return nullptr;
+  }
+  nsIWidget* window = RootReferenceFrame()->GetNearestWidget();
+  if (window) {
+    return window->GetLayerManager();
+  }
+  return nullptr;
+}
+
+/**
+ * We paint by executing a layer manager transaction, constructing a
+ * single layer representing the display list, and then making it the
+ * root of the layer manager, drawing into the PaintedLayers.
+ */
+already_AddRefed<LayerManager> nsDisplayList::PaintRoot(nsDisplayListBuilder* aBuilder,
+                                                        nsRenderingContext* aCtx,
+                                                        uint32_t aFlags) {
+  PROFILER_LABEL("nsDisplayList", "PaintRoot",
+    js::ProfileEntry::Category::GRAPHICS);
+
+  RefPtr<LayerManager> layerManager;
+  bool widgetTransaction = false;
+  bool doBeginTransaction = true;
+  nsView *view = nullptr;
+  if (aFlags & PAINT_USE_WIDGET_LAYERS) {
+    layerManager = aBuilder->GetWidgetLayerManager(&view);
+    if (layerManager) {
+      doBeginTransaction = !(aFlags & PAINT_EXISTING_TRANSACTION);
+      widgetTransaction = true;
+    }
+  }
+  if (!layerManager) {
+    if (!aCtx) {
+      NS_WARNING("Nowhere to paint into");
+      return nullptr;
+    }
+    layerManager = new BasicLayerManager(BasicLayerManager::BLM_OFFSCREEN);
+  }
+
+  // Store the existing layer builder to reinstate it on return.
+  FrameLayerBuilder *oldBuilder = layerManager->GetLayerBuilder();
+
+  FrameLayerBuilder *layerBuilder = new FrameLayerBuilder();
+  layerBuilder->Init(aBuilder, layerManager);
+
+  if (aFlags & PAINT_COMPRESSED) {
+    layerBuilder->SetLayerTreeCompressionMode();
+  }
+
+  if (doBeginTransaction) {
+    if (aCtx) {
+      if (!layerManager->BeginTransactionWithTarget(aCtx->ThebesContext())) {
+        return nullptr;
+      }
+    } else {
+      if (!layerManager->BeginTransaction()) {
+        return nullptr;
+      }
+    }
+  }
+
+  if (XRE_IsContentProcess() && gfxPrefs::AlwaysPaint()) {
+    FrameLayerBuilder::InvalidateAllLayers(layerManager);
+  }
+
+  if (widgetTransaction) {
+    layerBuilder->DidBeginRetainedLayerTransaction(layerManager);
+  }
+
+  nsIFrame* frame = aBuilder->RootReferenceFrame();
+  nsPresContext* presContext = frame->PresContext();
+  nsIPresShell* presShell = presContext->PresShell();
+  nsRootPresContext* rootPresContext = presContext->GetRootPresContext();
+
+  NotifySubDocInvalidationFunc computeInvalidFunc =
+    presContext->MayHavePaintEventListenerInSubDocument() ? nsPresContext::NotifySubDocInvalidation : 0;
+  bool computeInvalidRect = (computeInvalidFunc ||
+                             (!layerManager->IsCompositingCheap() && layerManager->NeedsWidgetInvalidation())) &&
+                            widgetTransaction;
+
+  UniquePtr<LayerProperties> props;
+  if (computeInvalidRect) {
+    props = Move(LayerProperties::CloneFrom(layerManager->GetRoot()));
+  }
+
+  // Clear any ScrollMetadata that may have been set on the root layer on a
+  // previous paint. This paint will set new metrics if necessary, and if we
+  // don't clear the old one here, we may be left with extra metrics.
+  if (Layer* root = layerManager->GetRoot()) {
+    root->SetScrollMetadata(nsTArray<ScrollMetadata>());
+  }
+
+  ContainerLayerParameters containerParameters
+    (presShell->GetResolution(), presShell->GetResolution());
+
+  RefPtr<ContainerLayer> root;
+  {
+    PaintTelemetry::AutoRecord record(PaintTelemetry::Metric::Layerization);
+    root = layerBuilder->
+      BuildContainerLayerFor(aBuilder, layerManager, frame, nullptr, this,
+                             containerParameters, nullptr);
+  }
+
+  nsIDocument* document = presShell->GetDocument();
+
+  if (!root) {
+    layerManager->SetUserData(&gLayerManagerLayerBuilder, oldBuilder);
+    return nullptr;
+  }
+  // Root is being scaled up by the X/Y resolution. Scale it back down.
+  root->SetPostScale(1.0f/containerParameters.mXScale,
+                     1.0f/containerParameters.mYScale);
+  root->SetScaleToResolution(presShell->ScaleToResolution(),
+      containerParameters.mXScale);
+  if (aBuilder->IsBuildingLayerEventRegions() &&
+      nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(presShell)) {
+    root->SetEventRegionsOverride(EventRegionsOverride::ForceDispatchToContent);
+  } else {
+    root->SetEventRegionsOverride(EventRegionsOverride::NoOverride);
+  }
+
+  // If we're using containerless scrolling, there is still one case where we
+  // want the root container layer to have metrics. If the parent process is
+  // using XUL windows, there is no root scrollframe, and without explicitly
+  // creating metrics there will be no guaranteed top-level APZC.
+  bool addMetrics = gfxPrefs::LayoutUseContainersForRootFrames() ||
+      (XRE_IsParentProcess() && !presShell->GetRootScrollFrame());
+
+  // Add metrics if there are none in the layer tree with the id (create an id
+  // if there isn't one already) of the root scroll frame/root content.
+  bool ensureMetricsForRootId =
+    nsLayoutUtils::AsyncPanZoomEnabled(frame) &&
+    !gfxPrefs::LayoutUseContainersForRootFrames() &&
+    aBuilder->IsPaintingToWindow() &&
+    !presContext->GetParentPresContext();
+
+  nsIContent* content = nullptr;
+  nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame();
+  if (rootScrollFrame) {
+    content = rootScrollFrame->GetContent();
+  } else {
+    // If there is no root scroll frame, pick the document element instead.
+    // The only case we don't want to do this is in non-APZ fennec, where
+    // we want the root xul document to get a null scroll id so that the root
+    // content document gets the first non-null scroll id.
+    content = document->GetDocumentElement();
+  }
+
+
+  if (ensureMetricsForRootId && content) {
+    ViewID scrollId = nsLayoutUtils::FindOrCreateIDFor(content);
+    if (nsLayoutUtils::ContainsMetricsWithId(root, scrollId)) {
+      ensureMetricsForRootId = false;
+    }
+  }
+
+  if (addMetrics || ensureMetricsForRootId) {
+    bool isRootContent = presContext->IsRootContentDocument();
+
+    nsRect viewport(aBuilder->ToReferenceFrame(frame), frame->GetSize());
+
+    root->SetScrollMetadata(
+      nsLayoutUtils::ComputeScrollMetadata(frame,
+                         rootScrollFrame, content,
+                         aBuilder->FindReferenceFrameFor(frame),
+                         root, FrameMetrics::NULL_SCROLL_ID, viewport, Nothing(),
+                         isRootContent, containerParameters));
+  }
+
+  // NS_WARNING is debug-only, so don't even bother checking the conditions in
+  // a release build.
+#ifdef DEBUG
+  bool usingDisplayport = false;
+  if (nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame()) {
+    nsIContent* content = rootScrollFrame->GetContent();
+    if (content) {
+      usingDisplayport = nsLayoutUtils::HasDisplayPort(content);
+    }
+  }
+  if (usingDisplayport &&
+      !(root->GetContentFlags() & Layer::CONTENT_OPAQUE) &&
+      SpammyLayoutWarningsEnabled()) {
+    // See bug 693938, attachment 567017
+    NS_WARNING("Transparent content with displayports can be expensive.");
+  }
+#endif
+
+  layerManager->SetRoot(root);
+  layerBuilder->WillEndTransaction();
+
+  if (widgetTransaction ||
+      // SVG-as-an-image docs don't paint as part of the retained layer tree,
+      // but they still need the invalidation state bits cleared in order for
+      // invalidation for CSS/SMIL animation to work properly.
+      (document && document->IsBeingUsedAsImage())) {
+    frame->ClearInvalidationStateBits();
+  }
+
+  bool temp = aBuilder->SetIsCompositingCheap(layerManager->IsCompositingCheap());
+  LayerManager::EndTransactionFlags flags = LayerManager::END_DEFAULT;
+  if (layerManager->NeedsWidgetInvalidation()) {
+    if (aFlags & PAINT_NO_COMPOSITE) {
+      flags = LayerManager::END_NO_COMPOSITE;
+    }
+  } else {
+    // Client layer managers never composite directly, so
+    // we don't need to worry about END_NO_COMPOSITE.
+    if (aBuilder->WillComputePluginGeometry()) {
+      flags = LayerManager::END_NO_REMOTE_COMPOSITE;
+    }
+  }
+
+  // If this is the content process, we ship plugin geometry updates over with layer
+  // updates, so calculate that now before we call EndTransaction.
+  if (rootPresContext && XRE_IsContentProcess()) {
+    if (aBuilder->WillComputePluginGeometry()) {
+      rootPresContext->ComputePluginGeometryUpdates(aBuilder->RootReferenceFrame(), aBuilder, this);
+    }
+    // The layer system caches plugin configuration information for forwarding
+    // with layer updates which needs to get set during reflow. This must be
+    // called even if there are no windowed plugins in the page.
+    rootPresContext->CollectPluginGeometryUpdates(layerManager);
+  }
+
+  MaybeSetupTransactionIdAllocator(layerManager, view);
+
+  layerManager->EndTransaction(FrameLayerBuilder::DrawPaintedLayer,
+                               aBuilder, flags);
+  aBuilder->SetIsCompositingCheap(temp);
+  layerBuilder->DidEndTransaction();
+
+  if (document && widgetTransaction) {
+    TriggerPendingAnimations(document, layerManager->GetAnimationReadyTime());
+  }
+
+  nsIntRegion invalid;
+  if (props) {
+    invalid = props->ComputeDifferences(root, computeInvalidFunc);
+  } else if (widgetTransaction) {
+    LayerProperties::ClearInvalidations(root);
+  }
+
+  bool shouldInvalidate = layerManager->NeedsWidgetInvalidation();
+  if (view) {
+    if (props) {
+      if (!invalid.IsEmpty()) {
+        nsIntRect bounds = invalid.GetBounds();
+        nsRect rect(presContext->DevPixelsToAppUnits(bounds.x),
+                    presContext->DevPixelsToAppUnits(bounds.y),
+                    presContext->DevPixelsToAppUnits(bounds.width),
+                    presContext->DevPixelsToAppUnits(bounds.height));
+        if (shouldInvalidate) {
+          view->GetViewManager()->InvalidateViewNoSuppression(view, rect);
+        }
+        presContext->NotifyInvalidation(bounds, 0);
+      }
+    } else if (shouldInvalidate) {
+      view->GetViewManager()->InvalidateView(view);
+    }
+  }
+
+  layerManager->SetUserData(&gLayerManagerLayerBuilder, oldBuilder);
+  return layerManager.forget();
+}
+
+uint32_t nsDisplayList::Count() const {
+  uint32_t count = 0;
+  for (nsDisplayItem* i = GetBottom(); i; i = i->GetAbove()) {
+    ++count;
+  }
+  return count;
+}
+
+nsDisplayItem* nsDisplayList::RemoveBottom() {
+  nsDisplayItem* item = mSentinel.mAbove;
+  if (!item)
+    return nullptr;
+  mSentinel.mAbove = item->mAbove;
+  if (item == mTop) {
+    // must have been the only item
+    mTop = &mSentinel;
+  }
+  item->mAbove = nullptr;
+  return item;
+}
+
+void nsDisplayList::DeleteAll() {
+  nsDisplayItem* item;
+  while ((item = RemoveBottom()) != nullptr) {
+    item->~nsDisplayItem();
+  }
+}
+
+static bool
+GetMouseThrough(const nsIFrame* aFrame)
+{
+  if (!aFrame->IsXULBoxFrame())
+    return false;
+
+  const nsIFrame* frame = aFrame;
+  while (frame) {
+    if (frame->GetStateBits() & NS_FRAME_MOUSE_THROUGH_ALWAYS) {
+      return true;
+    } else if (frame->GetStateBits() & NS_FRAME_MOUSE_THROUGH_NEVER) {
+      return false;
+    }
+    frame = nsBox::GetParentXULBox(frame);
+  }
+  return false;
+}
+
+static bool
+IsFrameReceivingPointerEvents(nsIFrame* aFrame)
+{
+  return NS_STYLE_POINTER_EVENTS_NONE !=
+    aFrame->StyleUserInterface()->GetEffectivePointerEvents(aFrame);
+}
+
+// A list of frames, and their z depth. Used for sorting
+// the results of hit testing.
+struct FramesWithDepth
+{
+  explicit FramesWithDepth(float aDepth) :
+    mDepth(aDepth)
+  {}
+
+  bool operator<(const FramesWithDepth& aOther) const {
+    if (!FuzzyEqual(mDepth, aOther.mDepth, 0.1f)) {
+      // We want to sort so that the shallowest item (highest depth value) is first
+      return mDepth > aOther.mDepth;
+    }
+    return this < &aOther;
+  }
+  bool operator==(const FramesWithDepth& aOther) const {
+    return this == &aOther;
+  }
+
+  float mDepth;
+  nsTArray<nsIFrame*> mFrames;
+};
+
+// Sort the frames by depth and then moves all the contained frames to the destination
+void FlushFramesArray(nsTArray<FramesWithDepth>& aSource, nsTArray<nsIFrame*>* aDest)
+{
+  if (aSource.IsEmpty()) {
+    return;
+  }
+  aSource.Sort();
+  uint32_t length = aSource.Length();
+  for (uint32_t i = 0; i < length; i++) {
+    aDest->AppendElements(Move(aSource[i].mFrames));
+  }
+  aSource.Clear();
+}
+
+void nsDisplayList::HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+                            nsDisplayItem::HitTestState* aState,
+                            nsTArray<nsIFrame*> *aOutFrames) const {
+  nsDisplayItem* item;
+
+  if (aState->mInPreserves3D) {
+    // Collect leaves of the current 3D rendering context.
+    for (item = GetBottom(); item; item = item->GetAbove()) {
+      auto itemType = item->GetType();
+      if (itemType != nsDisplayItem::TYPE_TRANSFORM ||
+          !static_cast<nsDisplayTransform*>(item)->IsLeafOf3DContext()) {
+        item->HitTest(aBuilder, aRect, aState, aOutFrames);
+      } else {
+        // One of leaves in the current 3D rendering context.
+        aState->mItemBuffer.AppendElement(item);
+      }
+    }
+    return;
+  }
+
+  int32_t itemBufferStart = aState->mItemBuffer.Length();
+  for (item = GetBottom(); item; item = item->GetAbove()) {
+    aState->mItemBuffer.AppendElement(item);
+  }
+
+  AutoTArray<FramesWithDepth, 16> temp;
+  for (int32_t i = aState->mItemBuffer.Length() - 1; i >= itemBufferStart; --i) {
+    // Pop element off the end of the buffer. We want to shorten the buffer
+    // so that recursive calls to HitTest have more buffer space.
+    item = aState->mItemBuffer[i];
+    aState->mItemBuffer.SetLength(i);
+
+    bool snap;
+    nsRect r = item->GetBounds(aBuilder, &snap).Intersect(aRect);
+    auto itemType = item->GetType();
+    bool same3DContext =
+      (itemType == nsDisplayItem::TYPE_TRANSFORM &&
+       static_cast<nsDisplayTransform*>(item)->IsParticipating3DContext()) ||
+      (itemType == nsDisplayItem::TYPE_PERSPECTIVE &&
+       item->Frame()->Extend3DContext());
+    if (same3DContext &&
+        (itemType != nsDisplayItem::TYPE_TRANSFORM ||
+         !static_cast<nsDisplayTransform*>(item)->IsLeafOf3DContext())) {
+      if (!item->GetClip().MayIntersect(aRect)) {
+        continue;
+      }
+      AutoTArray<nsIFrame*, 1> neverUsed;
+      // Start gethering leaves of the 3D rendering context, and
+      // append leaves at the end of mItemBuffer.  Leaves are
+      // processed at following iterations.
+      aState->mInPreserves3D = true;
+      item->HitTest(aBuilder, aRect, aState, &neverUsed);
+      aState->mInPreserves3D = false;
+      i = aState->mItemBuffer.Length();
+      continue;
+    }
+    if (same3DContext || item->GetClip().MayIntersect(r)) {
+      AutoTArray<nsIFrame*, 16> outFrames;
+      item->HitTest(aBuilder, aRect, aState, &outFrames);
+
+      // For 3d transforms with preserve-3d we add hit frames into the temp list
+      // so we can sort them later, otherwise we add them directly to the output list.
+      nsTArray<nsIFrame*> *writeFrames = aOutFrames;
+      if (item->GetType() == nsDisplayItem::TYPE_TRANSFORM &&
+          static_cast<nsDisplayTransform*>(item)->IsLeafOf3DContext()) {
+        if (outFrames.Length()) {
+          nsDisplayTransform *transform = static_cast<nsDisplayTransform*>(item);
+          nsPoint point = aRect.TopLeft();
+          // A 1x1 rect means a point, otherwise use the center of the rect
+          if (aRect.width != 1 || aRect.height != 1) {
+            point = aRect.Center();
+          }
+          temp.AppendElement(FramesWithDepth(transform->GetHitDepthAtPoint(aBuilder, point)));
+          writeFrames = &temp[temp.Length() - 1].mFrames;
+        }
+      } else {
+        // We may have just finished a run of consecutive preserve-3d transforms,
+        // so flush these into the destination array before processing our frame list.
+        FlushFramesArray(temp, aOutFrames);
+      }
+
+      for (uint32_t j = 0; j < outFrames.Length(); j++) {
+        nsIFrame *f = outFrames.ElementAt(j);
+        // Handle the XUL 'mousethrough' feature and 'pointer-events'.
+        if (!GetMouseThrough(f) && IsFrameReceivingPointerEvents(f)) {
+          writeFrames->AppendElement(f);
+        }
+      }
+    }
+  }
+  // Clear any remaining preserve-3d transforms.
+  FlushFramesArray(temp, aOutFrames);
+  NS_ASSERTION(aState->mItemBuffer.Length() == uint32_t(itemBufferStart),
+               "How did we forget to pop some elements?");
+}
+
+static void Sort(nsDisplayList* aList, int32_t aCount, nsDisplayList::SortLEQ aCmp,
+                 void* aClosure) {
+  if (aCount < 2)
+    return;
+
+  nsDisplayList list1;
+  nsDisplayList list2;
+  int i;
+  int32_t half = aCount/2;
+  bool sorted = true;
+  nsDisplayItem* prev = nullptr;
+  for (i = 0; i < aCount; ++i) {
+    nsDisplayItem* item = aList->RemoveBottom();
+    (i < half ? &list1 : &list2)->AppendToTop(item);
+    if (sorted && prev && !aCmp(prev, item, aClosure)) {
+      sorted = false;
+    }
+    prev = item;
+  }
+  if (sorted) {
+    aList->AppendToTop(&list1);
+    aList->AppendToTop(&list2);
+    return;
+  }
+
+  Sort(&list1, half, aCmp, aClosure);
+  Sort(&list2, aCount - half, aCmp, aClosure);
+
+  for (i = 0; i < aCount; ++i) {
+    if (list1.GetBottom() &&
+        (!list2.GetBottom() ||
+         aCmp(list1.GetBottom(), list2.GetBottom(), aClosure))) {
+      aList->AppendToTop(list1.RemoveBottom());
+    } else {
+      aList->AppendToTop(list2.RemoveBottom());
+    }
+  }
+}
+
+static nsIContent* FindContentInDocument(nsDisplayItem* aItem, nsIDocument* aDoc) {
+  nsIFrame* f = aItem->Frame();
+  while (f) {
+    nsPresContext* pc = f->PresContext();
+    if (pc->Document() == aDoc) {
+      return f->GetContent();
+    }
+    f = nsLayoutUtils::GetCrossDocParentFrame(pc->PresShell()->GetRootFrame());
+  }
+  return nullptr;
+}
+
+static bool IsContentLEQ(nsDisplayItem* aItem1, nsDisplayItem* aItem2,
+                         void* aClosure) {
+  nsIContent* commonAncestor = static_cast<nsIContent*>(aClosure);
+  // It's possible that the nsIContent for aItem1 or aItem2 is in a subdocument
+  // of commonAncestor, because display items for subdocuments have been
+  // mixed into the same list. Ensure that we're looking at content
+  // in commonAncestor's document.
+  nsIDocument* commonAncestorDoc = commonAncestor->OwnerDoc();
+  nsIContent* content1 = FindContentInDocument(aItem1, commonAncestorDoc);
+  nsIContent* content2 = FindContentInDocument(aItem2, commonAncestorDoc);
+  if (!content1 || !content2) {
+    NS_ERROR("Document trees are mixed up!");
+    // Something weird going on
+    return true;
+  }
+  return nsLayoutUtils::CompareTreePosition(content1, content2, commonAncestor) <= 0;
+}
+
+static bool IsZOrderLEQ(nsDisplayItem* aItem1, nsDisplayItem* aItem2,
+                        void* aClosure) {
+  // Note that we can't just take the difference of the two
+  // z-indices here, because that might overflow a 32-bit int.
+  return aItem1->ZIndex() <= aItem2->ZIndex();
+}
+
+void nsDisplayList::SortByZOrder() {
+  Sort(IsZOrderLEQ, nullptr);
+}
+
+void nsDisplayList::SortByContentOrder(nsIContent* aCommonAncestor) {
+  Sort(IsContentLEQ, aCommonAncestor);
+}
+
+void nsDisplayList::Sort(SortLEQ aCmp, void* aClosure) {
+  ::Sort(this, Count(), aCmp, aClosure);
+}
+
+nsDisplayItem::nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+ : nsDisplayItem(aBuilder, aFrame, aBuilder->ClipState().GetCurrentInnermostScrollClip())
+{}
+
+nsDisplayItem::nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                             const DisplayItemScrollClip* aScrollClip)
+  : mFrame(aFrame)
+  , mClip(aBuilder->ClipState().GetCurrentCombinedClip(aBuilder))
+  , mScrollClip(aScrollClip)
+  , mAnimatedGeometryRoot(nullptr)
+  , mForceNotVisible(aBuilder->IsBuildingInvisibleItems())
+#ifdef MOZ_DUMP_PAINTING
+  , mPainted(false)
+#endif
+{
+  mReferenceFrame = aBuilder->FindReferenceFrameFor(aFrame, &mToReferenceFrame);
+  // This can return the wrong result if the item override ShouldFixToViewport(),
+  // the item needs to set it again in its constructor.
+  mAnimatedGeometryRoot = aBuilder->FindAnimatedGeometryRootFor(aFrame);
+  MOZ_ASSERT(nsLayoutUtils::IsAncestorFrameCrossDoc(aBuilder->RootReferenceFrame(),
+                                                    *mAnimatedGeometryRoot), "Bad");
+  NS_ASSERTION(aBuilder->GetDirtyRect().width >= 0 ||
+               !aBuilder->IsForPainting(), "dirty rect not set");
+  // The dirty rect is for mCurrentFrame, so we have to use
+  // mCurrentOffsetToReferenceFrame
+  mVisibleRect = aBuilder->GetDirtyRect() +
+      aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+}
+
+/* static */ bool
+nsDisplayItem::ForceActiveLayers()
+{
+  static bool sForce = false;
+  static bool sForceCached = false;
+
+  if (!sForceCached) {
+    Preferences::AddBoolVarCache(&sForce, "layers.force-active", false);
+    sForceCached = true;
+  }
+
+  return sForce;
+}
+
+static int32_t ZIndexForFrame(nsIFrame* aFrame)
+{
+  if (!aFrame->IsAbsPosContainingBlock() && !aFrame->IsFlexOrGridItem())
+    return 0;
+
+  const nsStylePosition* position = aFrame->StylePosition();
+  if (position->mZIndex.GetUnit() == eStyleUnit_Integer)
+    return position->mZIndex.GetIntValue();
+
+  // sort the auto and 0 elements together
+  return 0;
+}
+
+int32_t
+nsDisplayItem::ZIndex() const
+{
+  return ZIndexForFrame(mFrame);
+}
+
+bool
+nsDisplayItem::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                 nsRegion* aVisibleRegion)
+{
+  return !mVisibleRect.IsEmpty() &&
+    !IsInvisibleInRect(aVisibleRegion->GetBounds());
+}
+
+bool
+nsDisplayItem::RecomputeVisibility(nsDisplayListBuilder* aBuilder,
+                                   nsRegion* aVisibleRegion) {
+  if (mForceNotVisible && !GetSameCoordinateSystemChildren()) {
+    // mForceNotVisible wants to ensure that this display item doesn't render
+    // anything itself. If this item has contents, then we obviously want to
+    // render those, so we don't need this check in that case.
+    NS_ASSERTION(mVisibleRect.IsEmpty(),
+      "invisible items without children should have empty vis rect");
+  } else {
+    nsRect bounds = GetClippedBounds(aBuilder);
+
+    nsRegion itemVisible;
+    itemVisible.And(*aVisibleRegion, bounds);
+    mVisibleRect = itemVisible.GetBounds();
+  }
+
+  // When we recompute visibility within layers we don't need to
+  // expand the visible region for content behind plugins (the plugin
+  // is not in the layer).
+  if (!ComputeVisibility(aBuilder, aVisibleRegion)) {
+    mVisibleRect = nsRect();
+    return false;
+  }
+
+  nsRegion opaque = TreatAsOpaque(this, aBuilder);
+  aBuilder->SubtractFromVisibleRegion(aVisibleRegion, opaque);
+  return true;
+}
+
+nsRect
+nsDisplayItem::GetClippedBounds(nsDisplayListBuilder* aBuilder)
+{
+  bool snap;
+  nsRect r = GetBounds(aBuilder, &snap);
+  return GetClip().ApplyNonRoundedIntersection(r);
+}
+
+nsRect
+nsDisplaySolidColor::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  *aSnap = true;
+  return mBounds;
+}
+
+void
+nsDisplaySolidColor::Paint(nsDisplayListBuilder* aBuilder,
+                           nsRenderingContext* aCtx)
+{
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  DrawTarget* drawTarget = aCtx->GetDrawTarget();
+  Rect rect =
+    NSRectToSnappedRect(mVisibleRect, appUnitsPerDevPixel, *drawTarget);
+  drawTarget->FillRect(rect, ColorPattern(ToDeviceColor(mColor)));
+}
+
+void
+nsDisplaySolidColor::WriteDebugInfo(std::stringstream& aStream)
+{
+  aStream << " (rgba "
+          << (int)NS_GET_R(mColor) << ","
+          << (int)NS_GET_G(mColor) << ","
+          << (int)NS_GET_B(mColor) << ","
+          << (int)NS_GET_A(mColor) << ")";
+}
+
+nsRect
+nsDisplaySolidColorRegion::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  *aSnap = true;
+  return mRegion.GetBounds();
+}
+
+void
+nsDisplaySolidColorRegion::Paint(nsDisplayListBuilder* aBuilder,
+                                 nsRenderingContext* aCtx)
+{
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  DrawTarget* drawTarget = aCtx->GetDrawTarget();
+  ColorPattern color(mColor);
+  for (auto iter = mRegion.RectIter(); !iter.Done(); iter.Next()) {
+    Rect rect =
+      NSRectToSnappedRect(iter.Get(), appUnitsPerDevPixel, *drawTarget);
+    drawTarget->FillRect(rect, color);
+  }
+}
+
+void
+nsDisplaySolidColorRegion::WriteDebugInfo(std::stringstream& aStream)
+{
+  aStream << " (rgba "
+          << int(mColor.r * 255) << ","
+          << int(mColor.g * 255) << ","
+          << int(mColor.b * 255) << ","
+          << mColor.a << ")";
+}
+
+static void
+RegisterThemeGeometry(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                      nsITheme::ThemeGeometryType aType)
+{
+  if (aBuilder->IsInChromeDocumentOrPopup() && !aBuilder->IsInTransform()) {
+    nsIFrame* displayRoot = nsLayoutUtils::GetDisplayRootFrame(aFrame);
+    nsPoint offset = aBuilder->IsInSubdocument() ? aBuilder->ToReferenceFrame(aFrame)
+                                                 : aFrame->GetOffsetTo(displayRoot);
+    nsRect borderBox = nsRect(offset, aFrame->GetSize());
+    aBuilder->RegisterThemeGeometry(aType,
+      LayoutDeviceIntRect::FromUnknownRect(
+        borderBox.ToNearestPixels(
+          aFrame->PresContext()->AppUnitsPerDevPixel())));
+  }
+}
+
+// Return the bounds of the viewport relative to |aFrame|'s reference frame.
+// Returns Nothing() if transforming into |aFrame|'s coordinate space fails.
+static Maybe<nsRect>
+GetViewportRectRelativeToReferenceFrame(nsDisplayListBuilder* aBuilder,
+                                        nsIFrame* aFrame)
+{
+  nsIFrame* rootFrame = aFrame->PresContext()->PresShell()->GetRootFrame();
+  nsRect rootRect = rootFrame->GetRectRelativeToSelf();
+  if (nsLayoutUtils::TransformRect(rootFrame, aFrame, rootRect) == nsLayoutUtils::TRANSFORM_SUCCEEDED) {
+    return Some(rootRect + aBuilder->ToReferenceFrame(aFrame));
+  }
+  return Nothing();
+}
+
+nsDisplayBackgroundImage::nsDisplayBackgroundImage(nsDisplayListBuilder* aBuilder,
+                                                   nsIFrame* aFrame,
+                                                   uint32_t aLayer,
+                                                   const nsRect& aBackgroundRect,
+                                                   const nsStyleBackground* aBackgroundStyle)
+  : nsDisplayImageContainer(aBuilder, aFrame)
+  , mBackgroundStyle(aBackgroundStyle)
+  , mBackgroundRect(aBackgroundRect)
+  , mLayer(aLayer)
+  , mIsRasterImage(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayBackgroundImage);
+
+  nsPresContext* presContext = mFrame->PresContext();
+  uint32_t flags = aBuilder->GetBackgroundPaintFlags();
+  const nsStyleImageLayers::Layer &layer = mBackgroundStyle->mImage.mLayers[mLayer];
+
+  bool isTransformedFixed;
+  nsBackgroundLayerState state =
+    nsCSSRendering::PrepareImageLayer(presContext, mFrame, flags,
+                                      mBackgroundRect, mBackgroundRect, layer,
+                                      &isTransformedFixed);
+  mShouldTreatAsFixed = ComputeShouldTreatAsFixed(isTransformedFixed);
+
+  mBounds = GetBoundsInternal(aBuilder);
+  if (ShouldFixToViewport(aBuilder)) {
+    mAnimatedGeometryRoot = aBuilder->FindAnimatedGeometryRootFor(this);
+
+    // Expand the item's visible rect to cover the entire bounds, limited to the
+    // viewport rect. This is necessary because the background's clip can move
+    // asynchronously.
+    if (Maybe<nsRect> viewportRect = GetViewportRectRelativeToReferenceFrame(aBuilder, mFrame)) {
+      mVisibleRect = mBounds.Intersect(*viewportRect);
+    }
+  }
+
+  mFillRect = state.mFillArea;
+  mDestRect = state.mDestArea;
+
+  nsImageRenderer* imageRenderer = &state.mImageRenderer;
+  // We only care about images here, not gradients.
+  if (imageRenderer->IsRasterImage()) {
+    mIsRasterImage = true;
+    mImage = imageRenderer->GetImage();
+  }
+}
+
+nsDisplayBackgroundImage::~nsDisplayBackgroundImage()
+{
+#ifdef NS_BUILD_REFCNT_LOGGING
+  MOZ_COUNT_DTOR(nsDisplayBackgroundImage);
+#endif
+}
+
+static nsStyleContext* GetBackgroundStyleContext(nsIFrame* aFrame)
+{
+  nsStyleContext *sc;
+  if (!nsCSSRendering::FindBackground(aFrame, &sc)) {
+    // We don't want to bail out if moz-appearance is set on a root
+    // node. If it has a parent content node, bail because it's not
+    // a root, other wise keep going in order to let the theme stuff
+    // draw the background. The canvas really should be drawing the
+    // bg, but there's no way to hook that up via css.
+    if (!aFrame->StyleDisplay()->mAppearance) {
+      return nullptr;
+    }
+
+    nsIContent* content = aFrame->GetContent();
+    if (!content || content->GetParent()) {
+      return nullptr;
+    }
+
+    sc = aFrame->StyleContext();
+  }
+  return sc;
+}
+
+/* static */ void
+SetBackgroundClipRegion(DisplayListClipState::AutoSaveRestore& aClipState,
+                        nsIFrame* aFrame, const nsPoint& aToReferenceFrame,
+                        const nsStyleImageLayers::Layer& aLayer,
+                        const nsRect& aBackgroundRect,
+                        bool aWillPaintBorder)
+{
+  nsCSSRendering::ImageLayerClipState clip;
+  nsCSSRendering::GetImageLayerClip(aLayer, aFrame, *aFrame->StyleBorder(),
+                                    aBackgroundRect, aBackgroundRect, aWillPaintBorder,
+                                    aFrame->PresContext()->AppUnitsPerDevPixel(),
+                                    &clip);
+
+  if (clip.mHasAdditionalBGClipArea) {
+    aClipState.ClipContentDescendants(clip.mAdditionalBGClipArea, clip.mBGClipArea,
+                                      clip.mHasRoundedCorners ? clip.mRadii : nullptr);
+  } else {
+    aClipState.ClipContentDescendants(clip.mBGClipArea, clip.mHasRoundedCorners ? clip.mRadii : nullptr);
+  }
+}
+
+/**
+ * This is used for the find bar highlighter overlay. It's only accessible
+ * through the AnonymousContent API, so it's not exposed to general web pages.
+ */
+static bool
+SpecialCutoutRegionCase(nsDisplayListBuilder* aBuilder,
+                        nsIFrame* aFrame,
+                        const nsRect& aBackgroundRect,
+                        nsDisplayList* aList,
+                        nscolor aColor)
+{
+  nsIContent* content = aFrame->GetContent();
+  if (!content) {
+    return false;
+  }
+
+  void* cutoutRegion = content->GetProperty(nsGkAtoms::cutoutregion);
+  if (!cutoutRegion) {
+    return false;
+  }
+
+  if (NS_GET_A(aColor) == 0) {
+    return true;
+  }
+
+  nsRegion region;
+  region.Sub(aBackgroundRect, *static_cast<nsRegion*>(cutoutRegion));
+  region.MoveBy(aBuilder->ToReferenceFrame(aFrame));
+  aList->AppendNewToTop(
+    new (aBuilder) nsDisplaySolidColorRegion(aBuilder, aFrame, region, aColor));
+
+  return true;
+}
+
+
+/*static*/ bool
+nsDisplayBackgroundImage::AppendBackgroundItemsToTop(nsDisplayListBuilder* aBuilder,
+                                                     nsIFrame* aFrame,
+                                                     const nsRect& aBackgroundRect,
+                                                     nsDisplayList* aList,
+                                                     bool aAllowWillPaintBorderOptimization,
+                                                     nsStyleContext* aStyleContext)
+{
+  nsStyleContext* bgSC = aStyleContext;
+  const nsStyleBackground* bg = nullptr;
+  nsRect bgRect = aBackgroundRect + aBuilder->ToReferenceFrame(aFrame);
+  nsPresContext* presContext = aFrame->PresContext();
+  bool isThemed = aFrame->IsThemed();
+  if (!isThemed) {
+    if (!bgSC) {
+      bgSC = GetBackgroundStyleContext(aFrame);
+    }
+    if (bgSC) {
+      bg = bgSC->StyleBackground();
+    }
+  }
+
+  bool drawBackgroundColor = false;
+  // Dummy initialisation to keep Valgrind/Memcheck happy.
+  // See bug 1122375 comment 1.
+  nscolor color = NS_RGBA(0,0,0,0);
+  if (!nsCSSRendering::IsCanvasFrame(aFrame) && bg) {
+    bool drawBackgroundImage;
+    color =
+      nsCSSRendering::DetermineBackgroundColor(presContext, bgSC, aFrame,
+                                               drawBackgroundImage, drawBackgroundColor);
+  }
+
+  if (SpecialCutoutRegionCase(aBuilder, aFrame, aBackgroundRect, aList, color)) {
+    return false;
+  }
+
+  const nsStyleBorder* borderStyle = aFrame->StyleBorder();
+  const nsStyleEffects* effectsStyle = aFrame->StyleEffects();
+  bool hasInsetShadow = effectsStyle->mBoxShadow &&
+                        effectsStyle->mBoxShadow->HasShadowWithInset(true);
+  bool willPaintBorder = aAllowWillPaintBorderOptimization &&
+                         !isThemed && !hasInsetShadow &&
+                         borderStyle->HasBorder();
+
+  nsPoint toRef = aBuilder->ToReferenceFrame(aFrame);
+
+  // An auxiliary list is necessary in case we have background blending; if that
+  // is the case, background items need to be wrapped by a blend container to
+  // isolate blending to the background
+  nsDisplayList bgItemList;
+  // Even if we don't actually have a background color to paint, we may still need
+  // to create an item for hit testing.
+  if ((drawBackgroundColor && color != NS_RGBA(0,0,0,0)) ||
+      aBuilder->IsForEventDelivery()) {
+    DisplayListClipState::AutoSaveRestore clipState(aBuilder);
+    if (bg && !aBuilder->IsForEventDelivery()) {
+      // Disable the will-paint-border optimization for background
+      // colors with no border-radius. Enabling it for background colors
+      // doesn't help much (there are no tiling issues) and clipping the
+      // background breaks detection of the element's border-box being
+      // opaque. For nonzero border-radius we still need it because we
+      // want to inset the background if possible to avoid antialiasing
+      // artifacts along the rounded corners.
+      bool useWillPaintBorderOptimization = willPaintBorder &&
+          nsLayoutUtils::HasNonZeroCorner(borderStyle->mBorderRadius);
+      SetBackgroundClipRegion(clipState, aFrame, toRef,
+                              bg->BottomLayer(), bgRect,
+                              useWillPaintBorderOptimization);
+    }
+    bgItemList.AppendNewToTop(
+        new (aBuilder) nsDisplayBackgroundColor(aBuilder, aFrame, bgRect, bg,
+                                                drawBackgroundColor ? color : NS_RGBA(0, 0, 0, 0)));
+  }
+
+  if (isThemed) {
+    nsITheme* theme = presContext->GetTheme();
+    if (theme->NeedToClearBackgroundBehindWidget(aFrame, aFrame->StyleDisplay()->mAppearance) &&
+        aBuilder->IsInChromeDocumentOrPopup() && !aBuilder->IsInTransform()) {
+      bgItemList.AppendNewToTop(
+        new (aBuilder) nsDisplayClearBackground(aBuilder, aFrame));
+    }
+    nsDisplayThemedBackground* bgItem =
+      new (aBuilder) nsDisplayThemedBackground(aBuilder, aFrame, bgRect);
+    bgItemList.AppendNewToTop(bgItem);
+    aList->AppendToTop(&bgItemList);
+    return true;
+  }
+
+  if (!bg) {
+    aList->AppendToTop(&bgItemList);
+    return false;
+  }
+
+  const DisplayItemScrollClip* scrollClip =
+    aBuilder->ClipState().GetCurrentInnermostScrollClip();
+
+  bool needBlendContainer = false;
+
+  // Passing bg == nullptr in this macro will result in one iteration with
+  // i = 0.
+  NS_FOR_VISIBLE_IMAGE_LAYERS_BACK_TO_FRONT(i, bg->mImage) {
+    if (bg->mImage.mLayers[i].mImage.IsEmpty()) {
+      continue;
+    }
+
+    if (bg->mImage.mLayers[i].mBlendMode != NS_STYLE_BLEND_NORMAL) {
+      needBlendContainer = true;
+    }
+
+    DisplayListClipState::AutoSaveRestore clipState(aBuilder);
+    if (!aBuilder->IsForEventDelivery()) {
+      const nsStyleImageLayers::Layer& layer = bg->mImage.mLayers[i];
+      SetBackgroundClipRegion(clipState, aFrame, toRef,
+                              layer, bgRect, willPaintBorder);
+    }
+
+    nsDisplayList thisItemList;
+    nsDisplayBackgroundImage* bgItem =
+      new (aBuilder) nsDisplayBackgroundImage(aBuilder, aFrame, i, bgRect, bg);
+
+    if (bgItem->ShouldFixToViewport(aBuilder)) {
+      thisItemList.AppendNewToTop(
+        nsDisplayFixedPosition::CreateForFixedBackground(aBuilder, aFrame, bgItem, i));
+    } else {
+      thisItemList.AppendNewToTop(bgItem);
+    }
+
+    if (bg->mImage.mLayers[i].mBlendMode != NS_STYLE_BLEND_NORMAL) {
+      thisItemList.AppendNewToTop(
+        new (aBuilder) nsDisplayBlendMode(aBuilder, aFrame, &thisItemList,
+                                          bg->mImage.mLayers[i].mBlendMode,
+                                          scrollClip, i + 1));
+    }
+    bgItemList.AppendToTop(&thisItemList);
+  }
+
+  if (needBlendContainer) {
+    bgItemList.AppendNewToTop(
+      nsDisplayBlendContainer::CreateForBackgroundBlendMode(aBuilder, aFrame, &bgItemList, scrollClip));
+  }
+
+  aList->AppendToTop(&bgItemList);
+  return false;
+}
+
+// Check that the rounded border of aFrame, added to aToReferenceFrame,
+// intersects aRect.  Assumes that the unrounded border has already
+// been checked for intersection.
+static bool
+RoundedBorderIntersectsRect(nsIFrame* aFrame,
+                            const nsPoint& aFrameToReferenceFrame,
+                            const nsRect& aTestRect)
+{
+  if (!nsRect(aFrameToReferenceFrame, aFrame->GetSize()).Intersects(aTestRect))
+    return false;
+
+  nscoord radii[8];
+  return !aFrame->GetBorderRadii(radii) ||
+         nsLayoutUtils::RoundedRectIntersectsRect(nsRect(aFrameToReferenceFrame,
+                                                  aFrame->GetSize()),
+                                                  radii, aTestRect);
+}
+
+// Returns TRUE if aContainedRect is guaranteed to be contained in
+// the rounded rect defined by aRoundedRect and aRadii. Complex cases are
+// handled conservatively by returning FALSE in some situations where
+// a more thorough analysis could return TRUE.
+//
+// See also RoundedRectIntersectsRect.
+static bool RoundedRectContainsRect(const nsRect& aRoundedRect,
+                                    const nscoord aRadii[8],
+                                    const nsRect& aContainedRect) {
+  nsRegion rgn = nsLayoutUtils::RoundedRectIntersectRect(aRoundedRect, aRadii, aContainedRect);
+  return rgn.Contains(aContainedRect);
+}
+
+bool
+nsDisplayBackgroundImage::ShouldTreatAsFixed() const
+{
+  return mShouldTreatAsFixed;
+}
+
+bool
+nsDisplayBackgroundImage::ComputeShouldTreatAsFixed(bool isTransformedFixed) const
+{
+  if (!mBackgroundStyle)
+    return false;
+
+  const nsStyleImageLayers::Layer &layer = mBackgroundStyle->mImage.mLayers[mLayer];
+  if (layer.mAttachment != NS_STYLE_IMAGELAYER_ATTACHMENT_FIXED)
+    return false;
+
+  // background-attachment:fixed is treated as background-attachment:scroll
+  // if it's affected by a transform.
+  // See https://www.w3.org/Bugs/Public/show_bug.cgi?id=17521.
+  return !isTransformedFixed;
+}
+
+bool
+nsDisplayBackgroundImage::IsNonEmptyFixedImage() const
+{
+  return ShouldTreatAsFixed() &&
+         !mBackgroundStyle->mImage.mLayers[mLayer].mImage.IsEmpty();
+}
+
+bool
+nsDisplayBackgroundImage::ShouldFixToViewport(nsDisplayListBuilder* aBuilder)
+{
+  // APZ needs background-attachment:fixed images layerized for correctness.
+  RefPtr<LayerManager> layerManager = aBuilder->GetWidgetLayerManager();
+  if (!nsLayoutUtils::UsesAsyncScrolling(mFrame) &&
+      layerManager && layerManager->ShouldAvoidComponentAlphaLayers()) {
+    return false;
+  }
+
+  // Put background-attachment:fixed background images in their own
+  // compositing layer.
+  return IsNonEmptyFixedImage();
+}
+
+bool
+nsDisplayBackgroundImage::CanOptimizeToImageLayer(LayerManager* aManager,
+                                                  nsDisplayListBuilder* aBuilder)
+{
+  if (!mBackgroundStyle) {
+    return false;
+  }
+
+  // We currently can't handle tiled backgrounds.
+  if (!mDestRect.Contains(mFillRect)) {
+    return false;
+  }
+
+  // For 'contain' and 'cover', we allow any pixel of the image to be sampled
+  // because there isn't going to be any spriting/atlasing going on.
+  const nsStyleImageLayers::Layer &layer = mBackgroundStyle->mImage.mLayers[mLayer];
+  bool allowPartialImages =
+    (layer.mSize.mWidthType == nsStyleImageLayers::Size::eContain ||
+     layer.mSize.mWidthType == nsStyleImageLayers::Size::eCover);
+  if (!allowPartialImages && !mFillRect.Contains(mDestRect)) {
+    return false;
+  }
+
+  return nsDisplayImageContainer::CanOptimizeToImageLayer(aManager, aBuilder);
+}
+
+nsRect
+nsDisplayBackgroundImage::GetDestRect()
+{
+  return mDestRect;
+}
+
+already_AddRefed<imgIContainer>
+nsDisplayBackgroundImage::GetImage()
+{
+  nsCOMPtr<imgIContainer> image = mImage;
+  return image.forget();
+}
+
+nsDisplayBackgroundImage::ImageLayerization
+nsDisplayBackgroundImage::ShouldCreateOwnLayer(nsDisplayListBuilder* aBuilder,
+                                               LayerManager* aManager)
+{
+  nsIFrame* backgroundStyleFrame = nsCSSRendering::FindBackgroundStyleFrame(mFrame);
+  if (ActiveLayerTracker::IsBackgroundPositionAnimated(aBuilder,
+                                                       backgroundStyleFrame)) {
+    return WHENEVER_POSSIBLE;
+  }
+
+  if (nsLayoutUtils::AnimatedImageLayersEnabled() && mBackgroundStyle) {
+    const nsStyleImageLayers::Layer &layer = mBackgroundStyle->mImage.mLayers[mLayer];
+    const nsStyleImage* image = &layer.mImage;
+    if (image->GetType() == eStyleImageType_Image) {
+      imgIRequest* imgreq = image->GetImageData();
+      nsCOMPtr<imgIContainer> image;
+      if (imgreq &&
+          NS_SUCCEEDED(imgreq->GetImage(getter_AddRefs(image))) &&
+          image) {
+        bool animated = false;
+        if (NS_SUCCEEDED(image->GetAnimated(&animated)) && animated) {
+          return WHENEVER_POSSIBLE;
+        }
+      }
+    }
+  }
+
+  if (nsLayoutUtils::GPUImageScalingEnabled() &&
+      aManager->IsCompositingCheap()) {
+    return ONLY_FOR_SCALING;
+  }
+
+  return NO_LAYER_NEEDED;
+}
+
+LayerState
+nsDisplayBackgroundImage::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                        LayerManager* aManager,
+                                        const ContainerLayerParameters& aParameters)
+{
+  ImageLayerization shouldLayerize = ShouldCreateOwnLayer(aBuilder, aManager);
+  if (shouldLayerize == NO_LAYER_NEEDED) {
+    // We can skip the call to CanOptimizeToImageLayer if we don't want a
+    // layer anyway.
+    return LAYER_NONE;
+  }
+
+  if (CanOptimizeToImageLayer(aManager, aBuilder)) {
+    if (shouldLayerize == WHENEVER_POSSIBLE) {
+      return LAYER_ACTIVE;
+    }
+
+    MOZ_ASSERT(shouldLayerize == ONLY_FOR_SCALING, "unhandled ImageLayerization value?");
+
+    MOZ_ASSERT(mImage);
+    int32_t imageWidth;
+    int32_t imageHeight;
+    mImage->GetWidth(&imageWidth);
+    mImage->GetHeight(&imageHeight);
+    NS_ASSERTION(imageWidth != 0 && imageHeight != 0, "Invalid image size!");
+  
+    int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+    LayoutDeviceRect destRect = LayoutDeviceRect::FromAppUnits(GetDestRect(), appUnitsPerDevPixel);
+
+    const LayerRect destLayerRect = destRect * aParameters.Scale();
+
+    // Calculate the scaling factor for the frame.
+    const gfxSize scale = gfxSize(destLayerRect.width / imageWidth,
+                                  destLayerRect.height / imageHeight);
+
+    if ((scale.width != 1.0f || scale.height != 1.0f) &&
+        (destLayerRect.width * destLayerRect.height >= 64 * 64)) {
+      // Separate this image into a layer.
+      // There's no point in doing this if we are not scaling at all or if the
+      // target size is pretty small.
+      return LAYER_ACTIVE;
+    }
+  }
+
+  return LAYER_NONE;
+}
+
+already_AddRefed<Layer>
+nsDisplayBackgroundImage::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                     LayerManager* aManager,
+                                     const ContainerLayerParameters& aParameters)
+{
+  RefPtr<ImageLayer> layer = static_cast<ImageLayer*>
+    (aManager->GetLayerBuilder()->GetLeafLayerFor(aBuilder, this));
+  if (!layer) {
+    layer = aManager->CreateImageLayer();
+    if (!layer)
+      return nullptr;
+  }
+  RefPtr<ImageContainer> imageContainer = GetContainer(aManager, aBuilder);
+  layer->SetContainer(imageContainer);
+  ConfigureLayer(layer, aParameters);
+  return layer.forget();
+}
+
+void
+nsDisplayBackgroundImage::HitTest(nsDisplayListBuilder* aBuilder,
+                                  const nsRect& aRect,
+                                  HitTestState* aState,
+                                  nsTArray<nsIFrame*> *aOutFrames)
+{
+  if (RoundedBorderIntersectsRect(mFrame, ToReferenceFrame(), aRect)) {
+    aOutFrames->AppendElement(mFrame);
+  }
+}
+
+bool
+nsDisplayBackgroundImage::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                            nsRegion* aVisibleRegion)
+{
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion)) {
+    return false;
+  }
+
+  // Return false if the background was propagated away from this
+  // frame. We don't want this display item to show up and confuse
+  // anything.
+  return mBackgroundStyle;
+}
+
+/* static */ nsRegion
+nsDisplayBackgroundImage::GetInsideClipRegion(nsDisplayItem* aItem,
+                                              uint8_t aClip,
+                                              const nsRect& aRect,
+                                              const nsRect& aBackgroundRect)
+{
+  nsRegion result;
+  if (aRect.IsEmpty())
+    return result;
+
+  nsIFrame *frame = aItem->Frame();
+
+  nsRect clipRect = aBackgroundRect;
+  if (frame->GetType() == nsGkAtoms::canvasFrame) {
+    nsCanvasFrame* canvasFrame = static_cast<nsCanvasFrame*>(frame);
+    clipRect = canvasFrame->CanvasArea() + aItem->ToReferenceFrame();
+  } else if (aClip == NS_STYLE_IMAGELAYER_CLIP_PADDING ||
+             aClip == NS_STYLE_IMAGELAYER_CLIP_CONTENT) {
+    nsMargin border = frame->GetUsedBorder();
+    if (aClip == NS_STYLE_IMAGELAYER_CLIP_CONTENT) {
+      border += frame->GetUsedPadding();
+    }
+    border.ApplySkipSides(frame->GetSkipSides());
+    clipRect.Deflate(border);
+  }
+
+  return clipRect.Intersect(aRect);
+}
+
+nsRegion
+nsDisplayBackgroundImage::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                          bool* aSnap) {
+  nsRegion result;
+  *aSnap = false;
+
+  if (!mBackgroundStyle)
+    return result;
+
+  *aSnap = true;
+
+  // For StyleBoxDecorationBreak::Slice, don't try to optimize here, since
+  // this could easily lead to O(N^2) behavior inside InlineBackgroundData,
+  // which expects frames to be sent to it in content order, not reverse
+  // content order which we'll produce here.
+  // Of course, if there's only one frame in the flow, it doesn't matter.
+  if (mFrame->StyleBorder()->mBoxDecorationBreak ==
+        StyleBoxDecorationBreak::Clone ||
+      (!mFrame->GetPrevContinuation() && !mFrame->GetNextContinuation())) {
+    const nsStyleImageLayers::Layer& layer = mBackgroundStyle->mImage.mLayers[mLayer];
+    if (layer.mImage.IsOpaque() && layer.mBlendMode == NS_STYLE_BLEND_NORMAL &&
+        layer.mRepeat.mXRepeat != NS_STYLE_IMAGELAYER_REPEAT_SPACE &&
+        layer.mRepeat.mYRepeat != NS_STYLE_IMAGELAYER_REPEAT_SPACE &&
+        layer.mClip != NS_STYLE_IMAGELAYER_CLIP_TEXT) {
+      result = GetInsideClipRegion(this, layer.mClip, mBounds, mBackgroundRect);
+    }
+  }
+
+  return result;
+}
+
+Maybe<nscolor>
+nsDisplayBackgroundImage::IsUniform(nsDisplayListBuilder* aBuilder) {
+  if (!mBackgroundStyle) {
+    return Some(NS_RGBA(0,0,0,0));
+  }
+  return Nothing();
+}
+
+nsRect
+nsDisplayBackgroundImage::GetPositioningArea()
+{
+  if (!mBackgroundStyle) {
+    return nsRect();
+  }
+  nsIFrame* attachedToFrame;
+  bool transformedFixed;
+  return nsCSSRendering::ComputeImageLayerPositioningArea(
+      mFrame->PresContext(), mFrame,
+      mBackgroundRect,
+      mBackgroundStyle->mImage.mLayers[mLayer],
+      &attachedToFrame,
+      &transformedFixed) + ToReferenceFrame();
+}
+
+bool
+nsDisplayBackgroundImage::RenderingMightDependOnPositioningAreaSizeChange()
+{
+  if (!mBackgroundStyle)
+    return false;
+
+  nscoord radii[8];
+  if (mFrame->GetBorderRadii(radii)) {
+    // A change in the size of the positioning area might change the position
+    // of the rounded corners.
+    return true;
+  }
+
+  const nsStyleImageLayers::Layer &layer = mBackgroundStyle->mImage.mLayers[mLayer];
+  if (layer.RenderingMightDependOnPositioningAreaSizeChange()) {
+    return true;
+  }
+  return false;
+}
+
+static void CheckForBorderItem(nsDisplayItem *aItem, uint32_t& aFlags)
+{
+  nsDisplayItem* nextItem = aItem->GetAbove();
+  while (nextItem && nextItem->GetType() == nsDisplayItem::TYPE_BACKGROUND) {
+    nextItem = nextItem->GetAbove();
+  }
+  if (nextItem &&
+      nextItem->Frame() == aItem->Frame() &&
+      nextItem->GetType() == nsDisplayItem::TYPE_BORDER) {
+    aFlags |= nsCSSRendering::PAINTBG_WILL_PAINT_BORDER;
+  }
+}
+
+void
+nsDisplayBackgroundImage::Paint(nsDisplayListBuilder* aBuilder,
+                                nsRenderingContext* aCtx) {
+  PaintInternal(aBuilder, aCtx, mVisibleRect, &mBounds);
+}
+
+void
+nsDisplayBackgroundImage::PaintInternal(nsDisplayListBuilder* aBuilder,
+                                        nsRenderingContext* aCtx, const nsRect& aBounds,
+                                        nsRect* aClipRect) {
+  uint32_t flags = aBuilder->GetBackgroundPaintFlags();
+  CheckForBorderItem(this, flags);
+
+  gfxContext* ctx = aCtx->ThebesContext();
+  uint8_t clip = mBackgroundStyle->mImage.mLayers[mLayer].mClip;
+
+  if (clip == NS_STYLE_IMAGELAYER_CLIP_TEXT) {
+    if (!GenerateAndPushTextMask(mFrame, aCtx, mBackgroundRect, aBuilder)) {
+      return;
+    }
+  }
+
+  nsCSSRendering::PaintBGParams params =
+    nsCSSRendering::PaintBGParams::ForSingleLayer(*mFrame->PresContext(),
+                                                  *aCtx,
+                                                  aBounds, mBackgroundRect,
+                                                  mFrame, flags, mLayer,
+                                                  CompositionOp::OP_OVER);
+  params.bgClipRect = aClipRect;
+  image::DrawResult result =
+    nsCSSRendering::PaintBackground(params);
+
+  if (clip == NS_STYLE_IMAGELAYER_CLIP_TEXT) {
+    ctx->PopGroupAndBlend();
+  }
+
+  nsDisplayBackgroundGeometry::UpdateDrawResult(this, result);
+}
+
+void nsDisplayBackgroundImage::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                                         const nsDisplayItemGeometry* aGeometry,
+                                                         nsRegion* aInvalidRegion)
+{
+  if (!mBackgroundStyle) {
+    return;
+  }
+
+  const nsDisplayBackgroundGeometry* geometry = static_cast<const nsDisplayBackgroundGeometry*>(aGeometry);
+
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+  nsRect positioningArea = GetPositioningArea();
+  if (positioningArea.TopLeft() != geometry->mPositioningArea.TopLeft() ||
+      (positioningArea.Size() != geometry->mPositioningArea.Size() &&
+       RenderingMightDependOnPositioningAreaSizeChange())) {
+    // Positioning area changed in a way that could cause everything to change,
+    // so invalidate everything (both old and new painting areas).
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+
+    if (positioningArea.Size() != geometry->mPositioningArea.Size()) {
+      NotifyRenderingChanged();
+    }
+    return;
+  }
+  if (!mDestRect.IsEqualInterior(geometry->mDestRect)) {
+    // Dest area changed in a way that could cause everything to change,
+    // so invalidate everything (both old and new painting areas).
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+    NotifyRenderingChanged();
+    return;
+  }
+  if (aBuilder->ShouldSyncDecodeImages()) {
+    const nsStyleImage& image = mBackgroundStyle->mImage.mLayers[mLayer].mImage;
+    if (image.GetType() == eStyleImageType_Image &&
+        geometry->ShouldInvalidateToSyncDecodeImages()) {
+      aInvalidRegion->Or(*aInvalidRegion, bounds);
+
+      NotifyRenderingChanged();
+    }
+  }
+  if (!bounds.IsEqualInterior(geometry->mBounds)) {
+    // Positioning area is unchanged, so invalidate just the change in the
+    // painting area.
+    aInvalidRegion->Xor(bounds, geometry->mBounds);
+
+    NotifyRenderingChanged();
+  }
+}
+
+nsRect
+nsDisplayBackgroundImage::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) {
+  *aSnap = true;
+  return mBounds;
+}
+
+nsRect
+nsDisplayBackgroundImage::GetBoundsInternal(nsDisplayListBuilder* aBuilder) {
+  nsPresContext* presContext = mFrame->PresContext();
+
+  if (!mBackgroundStyle) {
+    return nsRect();
+  }
+
+  nsRect clipRect = mBackgroundRect;
+  if (mFrame->GetType() == nsGkAtoms::canvasFrame) {
+    nsCanvasFrame* frame = static_cast<nsCanvasFrame*>(mFrame);
+    clipRect = frame->CanvasArea() + ToReferenceFrame();
+  } else if (nsLayoutUtils::UsesAsyncScrolling(mFrame) && IsNonEmptyFixedImage()) {
+    // If this is a background-attachment:fixed image, and APZ is enabled,
+    // async scrolling could reveal additional areas of the image, so don't
+    // clip it beyond clipping to the document's viewport.
+    if (Maybe<nsRect> viewportRect = GetViewportRectRelativeToReferenceFrame(aBuilder, mFrame)) {
+      clipRect = clipRect.Union(*viewportRect);
+    }
+  }
+  const nsStyleImageLayers::Layer& layer = mBackgroundStyle->mImage.mLayers[mLayer];
+  return nsCSSRendering::GetBackgroundLayerRect(presContext, mFrame,
+                                                mBackgroundRect, clipRect, layer,
+                                                aBuilder->GetBackgroundPaintFlags());
+}
+
+uint32_t
+nsDisplayBackgroundImage::GetPerFrameKey()
+{
+  return (mLayer << nsDisplayItem::TYPE_BITS) |
+    nsDisplayItem::GetPerFrameKey();
+}
+
+nsDisplayThemedBackground::nsDisplayThemedBackground(nsDisplayListBuilder* aBuilder,
+                                                     nsIFrame* aFrame,
+                                                     const nsRect& aBackgroundRect)
+  : nsDisplayItem(aBuilder, aFrame)
+  , mBackgroundRect(aBackgroundRect)
+{
+  MOZ_COUNT_CTOR(nsDisplayThemedBackground);
+
+  const nsStyleDisplay* disp = mFrame->StyleDisplay();
+  mAppearance = disp->mAppearance;
+  mFrame->IsThemed(disp, &mThemeTransparency);
+
+  // Perform necessary RegisterThemeGeometry
+  nsITheme* theme = mFrame->PresContext()->GetTheme();
+  nsITheme::ThemeGeometryType type =
+    theme->ThemeGeometryTypeForWidget(mFrame, disp->mAppearance);
+  if (type != nsITheme::eThemeGeometryTypeUnknown) {
+    RegisterThemeGeometry(aBuilder, aFrame, type);
+  }
+
+  if (disp->mAppearance == NS_THEME_WIN_BORDERLESS_GLASS ||
+      disp->mAppearance == NS_THEME_WIN_GLASS) {
+    aBuilder->SetGlassDisplayItem(this);
+  }
+
+  mBounds = GetBoundsInternal();
+}
+
+nsDisplayThemedBackground::~nsDisplayThemedBackground()
+{
+#ifdef NS_BUILD_REFCNT_LOGGING
+  MOZ_COUNT_DTOR(nsDisplayThemedBackground);
+#endif
+}
+
+void
+nsDisplayThemedBackground::WriteDebugInfo(std::stringstream& aStream)
+{
+  aStream << " (themed, appearance:" << (int)mAppearance << ")";
+}
+
+void
+nsDisplayThemedBackground::HitTest(nsDisplayListBuilder* aBuilder,
+                                  const nsRect& aRect,
+                                  HitTestState* aState,
+                                  nsTArray<nsIFrame*> *aOutFrames)
+{
+  // Assume that any point in our background rect is a hit.
+  if (mBackgroundRect.Intersects(aRect)) {
+    aOutFrames->AppendElement(mFrame);
+  }
+}
+
+nsRegion
+nsDisplayThemedBackground::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                           bool* aSnap) {
+  nsRegion result;
+  *aSnap = false;
+
+  if (mThemeTransparency == nsITheme::eOpaque) {
+    result = mBackgroundRect;
+  }
+  return result;
+}
+
+Maybe<nscolor>
+nsDisplayThemedBackground::IsUniform(nsDisplayListBuilder* aBuilder) {
+  if (mAppearance == NS_THEME_WIN_BORDERLESS_GLASS ||
+      mAppearance == NS_THEME_WIN_GLASS) {
+    return Some(NS_RGBA(0,0,0,0));
+  }
+  return Nothing();
+}
+
+bool
+nsDisplayThemedBackground::ProvidesFontSmoothingBackgroundColor(nscolor* aColor)
+{
+  nsITheme* theme = mFrame->PresContext()->GetTheme();
+  return theme->WidgetProvidesFontSmoothingBackgroundColor(mFrame, mAppearance, aColor);
+}
+
+nsRect
+nsDisplayThemedBackground::GetPositioningArea()
+{
+  return mBackgroundRect;
+}
+
+void
+nsDisplayThemedBackground::Paint(nsDisplayListBuilder* aBuilder,
+                                 nsRenderingContext* aCtx)
+{
+  PaintInternal(aBuilder, aCtx, mVisibleRect, nullptr);
+}
+
+
+void
+nsDisplayThemedBackground::PaintInternal(nsDisplayListBuilder* aBuilder,
+                                         nsRenderingContext* aCtx, const nsRect& aBounds,
+                                         nsRect* aClipRect)
+{
+  // XXXzw this ignores aClipRect.
+  nsPresContext* presContext = mFrame->PresContext();
+  nsITheme *theme = presContext->GetTheme();
+  nsRect drawing(mBackgroundRect);
+  theme->GetWidgetOverflow(presContext->DeviceContext(), mFrame, mAppearance,
+                           &drawing);
+  drawing.IntersectRect(drawing, aBounds);
+  theme->DrawWidgetBackground(aCtx, mFrame, mAppearance, mBackgroundRect, drawing);
+}
+
+bool nsDisplayThemedBackground::IsWindowActive()
+{
+  EventStates docState = mFrame->GetContent()->OwnerDoc()->GetDocumentState();
+  return !docState.HasState(NS_DOCUMENT_STATE_WINDOW_INACTIVE);
+}
+
+void nsDisplayThemedBackground::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                                          const nsDisplayItemGeometry* aGeometry,
+                                                          nsRegion* aInvalidRegion)
+{
+  const nsDisplayThemedBackgroundGeometry* geometry = static_cast<const nsDisplayThemedBackgroundGeometry*>(aGeometry);
+
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+  nsRect positioningArea = GetPositioningArea();
+  if (!positioningArea.IsEqualInterior(geometry->mPositioningArea)) {
+    // Invalidate everything (both old and new painting areas).
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+    return;
+  }
+  if (!bounds.IsEqualInterior(geometry->mBounds)) {
+    // Positioning area is unchanged, so invalidate just the change in the
+    // painting area.
+    aInvalidRegion->Xor(bounds, geometry->mBounds);
+  }
+  nsITheme* theme = mFrame->PresContext()->GetTheme();
+  if (theme->WidgetAppearanceDependsOnWindowFocus(mAppearance) &&
+      IsWindowActive() != geometry->mWindowIsActive) {
+    aInvalidRegion->Or(*aInvalidRegion, bounds);
+  }
+}
+
+nsRect
+nsDisplayThemedBackground::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) {
+  *aSnap = true;
+  return mBounds;
+}
+
+nsRect
+nsDisplayThemedBackground::GetBoundsInternal() {
+  nsPresContext* presContext = mFrame->PresContext();
+
+  nsRect r = mBackgroundRect - ToReferenceFrame();
+  presContext->GetTheme()->
+      GetWidgetOverflow(presContext->DeviceContext(), mFrame,
+                        mFrame->StyleDisplay()->mAppearance, &r);
+  return r + ToReferenceFrame();
+}
+
+void
+nsDisplayImageContainer::ConfigureLayer(ImageLayer* aLayer,
+                                        const ContainerLayerParameters& aParameters)
+{
+  aLayer->SetSamplingFilter(nsLayoutUtils::GetSamplingFilterForFrame(mFrame));
+
+  nsCOMPtr<imgIContainer> image = GetImage();
+  MOZ_ASSERT(image);
+  int32_t imageWidth;
+  int32_t imageHeight;
+  image->GetWidth(&imageWidth);
+  image->GetHeight(&imageHeight);
+  NS_ASSERTION(imageWidth != 0 && imageHeight != 0, "Invalid image size!");
+
+  if (imageWidth > 0 && imageHeight > 0) {
+    // We're actually using the ImageContainer. Let our frame know that it
+    // should consider itself to have painted successfully.
+    nsDisplayBackgroundGeometry::UpdateDrawResult(this,
+                                                  image::DrawResult::SUCCESS);
+  }
+
+  // XXX(seth): Right now we ignore aParameters.Scale() and
+  // aParameters.Offset(), because FrameLayerBuilder already applies
+  // aParameters.Scale() via the layer's post-transform, and
+  // aParameters.Offset() is always zero.
+  MOZ_ASSERT(aParameters.Offset() == LayerIntPoint(0,0));
+
+  // It's possible (for example, due to downscale-during-decode) that the
+  // ImageContainer this ImageLayer is holding has a different size from the
+  // intrinsic size of the image. For this reason we compute the transform using
+  // the ImageContainer's size rather than the image's intrinsic size.
+  // XXX(seth): In reality, since the size of the ImageContainer may change
+  // asynchronously, this is not enough. Bug 1183378 will provide a more
+  // complete fix, but this solution is safe in more cases than simply relying
+  // on the intrinsic size.
+  IntSize containerSize = aLayer->GetContainer()
+                        ? aLayer->GetContainer()->GetCurrentSize()
+                        : IntSize(imageWidth, imageHeight);
+  
+  const int32_t factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  const LayoutDeviceRect destRect =
+    LayoutDeviceRect::FromAppUnits(GetDestRect(), factor);
+
+  const LayoutDevicePoint p = destRect.TopLeft();
+  Matrix transform = Matrix::Translation(p.x, p.y);
+  transform.PreScale(destRect.width / containerSize.width,
+                     destRect.height / containerSize.height);
+  aLayer->SetBaseTransform(gfx::Matrix4x4::From2D(transform));
+}
+
+already_AddRefed<ImageContainer>
+nsDisplayImageContainer::GetContainer(LayerManager* aManager,
+                                      nsDisplayListBuilder *aBuilder)
+{
+  nsCOMPtr<imgIContainer> image = GetImage();
+  if (!image) {
+    MOZ_ASSERT_UNREACHABLE("Must call CanOptimizeToImage() and get true "
+                           "before calling GetContainer()");
+    return nullptr;
+  }
+
+  uint32_t flags = aBuilder->ShouldSyncDecodeImages()
+                 ? imgIContainer::FLAG_SYNC_DECODE
+                 : imgIContainer::FLAG_NONE;
+
+  return image->GetImageContainer(aManager, flags);
+}
+
+bool
+nsDisplayImageContainer::CanOptimizeToImageLayer(LayerManager* aManager,
+                                                 nsDisplayListBuilder* aBuilder)
+{
+  uint32_t flags = aBuilder->ShouldSyncDecodeImages()
+                 ? imgIContainer::FLAG_SYNC_DECODE
+                 : imgIContainer::FLAG_NONE;
+
+  nsCOMPtr<imgIContainer> image = GetImage();
+  if (!image) {
+    return false;
+  }
+
+  if (!image->IsImageContainerAvailable(aManager, flags)) {
+    return false;
+  }
+
+  int32_t imageWidth;
+  int32_t imageHeight;
+  image->GetWidth(&imageWidth);
+  image->GetHeight(&imageHeight);
+
+  if (imageWidth == 0 || imageHeight == 0) {
+    NS_ASSERTION(false, "invalid image size");
+    return false;
+  }
+
+  const int32_t factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  const LayoutDeviceRect destRect =
+    LayoutDeviceRect::FromAppUnits(GetDestRect(), factor);
+
+  // Calculate the scaling factor for the frame.
+  const gfxSize scale = gfxSize(destRect.width / imageWidth,
+                                destRect.height / imageHeight);
+
+  if (scale.width < 0.34 || scale.height < 0.34) {
+    // This would look awful as long as we can't use high-quality downscaling
+    // for image layers (bug 803703), so don't turn this into an image layer.
+    return false;
+  }
+
+  return true;
+}
+
+void
+nsDisplayBackgroundColor::ApplyOpacity(nsDisplayListBuilder* aBuilder,
+                                       float aOpacity,
+                                       const DisplayItemClip* aClip)
+{
+  NS_ASSERTION(CanApplyOpacity(), "ApplyOpacity should be allowed");
+  mColor.a = mColor.a * aOpacity;
+  if (aClip) {
+    IntersectClip(aBuilder, *aClip);
+  }
+}
+
+bool
+nsDisplayBackgroundColor::CanApplyOpacity() const
+{
+  return true;
+}
+
+void
+nsDisplayBackgroundColor::Paint(nsDisplayListBuilder* aBuilder,
+                                nsRenderingContext* aCtx)
+{
+  if (mColor == Color()) {
+    return;
+  }
+
+#if 0
+  // See https://bugzilla.mozilla.org/show_bug.cgi?id=1148418#c21 for why this
+  // results in a precision induced rounding issue that makes the rect one
+  // pixel shorter in rare cases. Disabled in favor of the old code for now.
+  // Note that the pref layout.css.devPixelsPerPx needs to be set to 1 to
+  // reproduce the bug.
+  //
+  // TODO:
+  // This new path does not include support for background-clip:text; need to
+  // be fixed if/when we switch to this new code path.
+
+  DrawTarget& aDrawTarget = *aCtx->GetDrawTarget();
+
+  Rect rect = NSRectToSnappedRect(mBackgroundRect,
+                                  mFrame->PresContext()->AppUnitsPerDevPixel(),
+                                  aDrawTarget);
+  ColorPattern color(ToDeviceColor(mColor));
+  aDrawTarget.FillRect(rect, color);
+#else
+  gfxContext* ctx = aCtx->ThebesContext();
+  gfxRect bounds =
+    nsLayoutUtils::RectToGfxRect(mBackgroundRect,
+                                 mFrame->PresContext()->AppUnitsPerDevPixel());
+
+  uint8_t clip = mBackgroundStyle->mImage.mLayers[0].mClip;
+  if (clip == NS_STYLE_IMAGELAYER_CLIP_TEXT) {
+    if (!GenerateAndPushTextMask(mFrame, aCtx, mBackgroundRect, aBuilder)) {
+      return;
+    }
+
+    ctx->SetColor(mColor);
+    ctx->Rectangle(bounds, true);
+    ctx->Fill();
+    ctx->PopGroupAndBlend();
+    return;
+  }
+
+  ctx->SetColor(mColor);
+  ctx->NewPath();
+  ctx->Rectangle(bounds, true);
+  ctx->Fill();
+#endif
+}
+
+nsRegion
+nsDisplayBackgroundColor::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                          bool* aSnap)
+{
+  *aSnap = false;
+
+  if (mColor.a != 1) {
+    return nsRegion();
+  }
+
+  if (!mBackgroundStyle)
+    return nsRegion();
+
+
+  const nsStyleImageLayers::Layer& bottomLayer = mBackgroundStyle->BottomLayer();
+  if (bottomLayer.mClip == NS_STYLE_IMAGELAYER_CLIP_TEXT) {
+    return nsRegion();
+  }
+
+  *aSnap = true;
+  return nsDisplayBackgroundImage::GetInsideClipRegion(this, bottomLayer.mClip,
+                                                       mBackgroundRect, mBackgroundRect);
+}
+
+Maybe<nscolor>
+nsDisplayBackgroundColor::IsUniform(nsDisplayListBuilder* aBuilder)
+{
+  return Some(mColor.ToABGR());
+}
+
+void
+nsDisplayBackgroundColor::HitTest(nsDisplayListBuilder* aBuilder,
+                                  const nsRect& aRect,
+                                  HitTestState* aState,
+                                  nsTArray<nsIFrame*> *aOutFrames)
+{
+  if (!RoundedBorderIntersectsRect(mFrame, ToReferenceFrame(), aRect)) {
+    // aRect doesn't intersect our border-radius curve.
+    return;
+  }
+
+  aOutFrames->AppendElement(mFrame);
+}
+
+void
+nsDisplayBackgroundColor::WriteDebugInfo(std::stringstream& aStream)
+{
+  aStream << " (rgba " << mColor.r << "," << mColor.g << ","
+          << mColor.b << "," << mColor.a << ")";
+}
+
+already_AddRefed<Layer>
+nsDisplayClearBackground::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                     LayerManager* aManager,
+                                     const ContainerLayerParameters& aParameters)
+{
+  RefPtr<ColorLayer> layer = static_cast<ColorLayer*>
+    (aManager->GetLayerBuilder()->GetLeafLayerFor(aBuilder, this));
+  if (!layer) {
+    layer = aManager->CreateColorLayer();
+    if (!layer)
+      return nullptr;
+  }
+  layer->SetColor(Color());
+  layer->SetMixBlendMode(gfx::CompositionOp::OP_SOURCE);
+
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  layer->SetBounds(bounds.ToNearestPixels(appUnitsPerDevPixel)); // XXX Do we need to respect the parent layer's scale here?
+
+  return layer.forget();
+}
+
+nsRect
+nsDisplayOutline::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) {
+  *aSnap = false;
+  return mFrame->GetVisualOverflowRectRelativeToSelf() + ToReferenceFrame();
+}
+
+void
+nsDisplayOutline::Paint(nsDisplayListBuilder* aBuilder,
+                        nsRenderingContext* aCtx) {
+  // TODO join outlines together
+  nsPoint offset = ToReferenceFrame();
+  nsCSSRendering::PaintOutline(mFrame->PresContext(), *aCtx, mFrame,
+                               mVisibleRect,
+                               nsRect(offset, mFrame->GetSize()),
+                               mFrame->StyleContext());
+}
+
+bool
+nsDisplayOutline::IsInvisibleInRect(const nsRect& aRect)
+{
+  const nsStyleOutline* outline = mFrame->StyleOutline();
+  nsRect borderBox(ToReferenceFrame(), mFrame->GetSize());
+  if (borderBox.Contains(aRect) &&
+      !nsLayoutUtils::HasNonZeroCorner(outline->mOutlineRadius)) {
+    if (outline->mOutlineOffset >= 0) {
+      // aRect is entirely inside the border-rect, and the outline isn't
+      // rendered inside the border-rect, so the outline is not visible.
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void
+nsDisplayEventReceiver::HitTest(nsDisplayListBuilder* aBuilder,
+                                const nsRect& aRect,
+                                HitTestState* aState,
+                                nsTArray<nsIFrame*> *aOutFrames)
+{
+  if (!RoundedBorderIntersectsRect(mFrame, ToReferenceFrame(), aRect)) {
+    // aRect doesn't intersect our border-radius curve.
+    return;
+  }
+
+  aOutFrames->AppendElement(mFrame);
+}
+
+void
+nsDisplayLayerEventRegions::AddFrame(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame)
+{
+  NS_ASSERTION(aBuilder->FindReferenceFrameFor(aFrame) == aBuilder->FindReferenceFrameFor(mFrame),
+               "Reference frame mismatch");
+  if (aBuilder->IsInsidePointerEventsNoneDoc()) {
+    // Somewhere up the parent document chain is a subdocument with pointer-
+    // events:none set on it.
+    return;
+  }
+  if (!aFrame->GetParent()) {
+    MOZ_ASSERT(aFrame->GetType() == nsGkAtoms::viewportFrame);
+    // Viewport frames are never event targets, other frames, like canvas frames,
+    // are the event targets for any regions viewport frames may cover.
+    return;
+  }
+
+  uint8_t pointerEvents =
+    aFrame->StyleUserInterface()->GetEffectivePointerEvents(aFrame);
+  if (pointerEvents == NS_STYLE_POINTER_EVENTS_NONE) {
+    return;
+  }
+  bool simpleRegions = aFrame->HasAnyStateBits(NS_FRAME_SIMPLE_EVENT_REGIONS);
+  if (!simpleRegions) {
+    if (!aFrame->StyleVisibility()->IsVisible()) {
+      return;
+    }
+  }
+  // XXX handle other pointerEvents values for SVG
+
+  // XXX Do something clever here for the common case where the border box
+  // is obviously entirely inside mHitRegion.
+  nsRect borderBox;
+  if (nsLayoutUtils::GetScrollableFrameFor(aFrame)) {
+    // If the frame is content of a scrollframe, then we need to pick up the
+    // area corresponding to the overflow rect as well. Otherwise the parts of
+    // the overflow that are not occupied by descendants get skipped and the
+    // APZ code sends touch events to the content underneath instead.
+    // See https://bugzilla.mozilla.org/show_bug.cgi?id=1127773#c15.
+    borderBox = aFrame->GetScrollableOverflowRect();
+  } else {
+    borderBox = nsRect(nsPoint(0, 0), aFrame->GetSize());
+  }
+  borderBox += aBuilder->ToReferenceFrame(aFrame);
+
+  bool borderBoxHasRoundedCorners = false;
+  if (!simpleRegions) {
+    if (nsLayoutUtils::HasNonZeroCorner(aFrame->StyleBorder()->mBorderRadius)) {
+      borderBoxHasRoundedCorners = true;
+    } else {
+      aFrame->AddStateBits(NS_FRAME_SIMPLE_EVENT_REGIONS);
+    }
+  }
+
+  const DisplayItemClip* clip = aBuilder->ClipState().GetCurrentCombinedClip(aBuilder);
+  if (clip) {
+    borderBox = clip->ApplyNonRoundedIntersection(borderBox);
+    if (clip->GetRoundedRectCount() > 0) {
+      borderBoxHasRoundedCorners = true;
+    }
+  }
+
+  if (borderBoxHasRoundedCorners ||
+      (aFrame->GetStateBits() & NS_FRAME_SVG_LAYOUT)) {
+    mMaybeHitRegion.Or(mMaybeHitRegion, borderBox);
+
+    // Avoid quadratic performance as a result of the region growing to include
+    // an arbitrarily large number of rects, which can happen on some pages.
+    mMaybeHitRegion.SimplifyOutward(8);
+  } else {
+    mHitRegion.Or(mHitRegion, borderBox);
+  }
+
+  if (aBuilder->IsBuildingNonLayerizedScrollbar() ||
+      aBuilder->GetAncestorHasApzAwareEventHandler())
+  {
+    // Scrollbars may be painted into a layer below the actual layer they will
+    // scroll, and therefore wheel events may be dispatched to the outer frame
+    // instead of the intended scrollframe. To address this, we force a d-t-c
+    // region on scrollbar frames that won't be placed in their own layer. See
+    // bug 1213324 for details.
+    mDispatchToContentHitRegion.Or(mDispatchToContentHitRegion, borderBox);
+  } else if (aFrame->GetType() == nsGkAtoms::objectFrame) {
+    // If the frame is a plugin frame and wants to handle wheel events as
+    // default action, we should add the frame to dispatch-to-content region.
+    nsPluginFrame* pluginFrame = do_QueryFrame(aFrame);
+    if (pluginFrame && pluginFrame->WantsToHandleWheelEventAsDefaultAction()) {
+      mDispatchToContentHitRegion.Or(mDispatchToContentHitRegion, borderBox);
+    }
+  }
+
+  // Touch action region
+
+  nsIFrame* touchActionFrame = aFrame;
+  nsIScrollableFrame* scrollFrame = nsLayoutUtils::GetScrollableFrameFor(aFrame);
+  if (scrollFrame) {
+    touchActionFrame = do_QueryFrame(scrollFrame);
+  }
+  uint32_t touchAction = nsLayoutUtils::GetTouchActionFromFrame(touchActionFrame);
+  if (touchAction != NS_STYLE_TOUCH_ACTION_AUTO) {
+    // If this frame has touch-action areas, and there were already
+    // touch-action areas from some other element on this same event regions,
+    // then all we know is that there are multiple elements with touch-action
+    // properties. In particular, we don't know what the relationship is
+    // between those elements in terms of DOM ancestry, and so we don't know
+    // how to combine the regions properly. Instead, we just add all the areas
+    // to the dispatch-to-content region, so that the APZ knows to check with
+    // the main thread. XXX we need to come up with a better way to do this,
+    // see bug 1287829.
+    bool alreadyHadRegions = !mNoActionRegion.IsEmpty() ||
+        !mHorizontalPanRegion.IsEmpty() ||
+        !mVerticalPanRegion.IsEmpty();
+    if (touchAction & NS_STYLE_TOUCH_ACTION_NONE) {
+      mNoActionRegion.OrWith(borderBox);
+    } else {
+      if ((touchAction & NS_STYLE_TOUCH_ACTION_PAN_X)) {
+        mHorizontalPanRegion.OrWith(borderBox);
+      }
+      if ((touchAction & NS_STYLE_TOUCH_ACTION_PAN_Y)) {
+        mVerticalPanRegion.OrWith(borderBox);
+      }
+    }
+    if (alreadyHadRegions) {
+      mDispatchToContentHitRegion.OrWith(CombinedTouchActionRegion());
+    }
+  }
+}
+
+void
+nsDisplayLayerEventRegions::AddInactiveScrollPort(const nsRect& aRect)
+{
+  mHitRegion.Or(mHitRegion, aRect);
+  mDispatchToContentHitRegion.Or(mDispatchToContentHitRegion, aRect);
+}
+
+bool
+nsDisplayLayerEventRegions::IsEmpty() const
+{
+  // If the hit region and maybe-hit region are empty, then the rest
+  // must be empty too.
+  if (mHitRegion.IsEmpty() && mMaybeHitRegion.IsEmpty()) {
+    MOZ_ASSERT(mDispatchToContentHitRegion.IsEmpty());
+    MOZ_ASSERT(mNoActionRegion.IsEmpty());
+    MOZ_ASSERT(mHorizontalPanRegion.IsEmpty());
+    MOZ_ASSERT(mVerticalPanRegion.IsEmpty());
+    return true;
+  }
+  return false;
+}
+
+nsRegion
+nsDisplayLayerEventRegions::CombinedTouchActionRegion()
+{
+  nsRegion result;
+  result.Or(mHorizontalPanRegion, mVerticalPanRegion);
+  result.OrWith(mNoActionRegion);
+  return result;
+}
+
+int32_t
+nsDisplayLayerEventRegions::ZIndex() const
+{
+  return mOverrideZIndex ? *mOverrideZIndex : nsDisplayItem::ZIndex();
+}
+
+void
+nsDisplayLayerEventRegions::SetOverrideZIndex(int32_t aZIndex)
+{
+  mOverrideZIndex = Some(aZIndex);
+}
+
+void
+nsDisplayLayerEventRegions::WriteDebugInfo(std::stringstream& aStream)
+{
+  if (!mHitRegion.IsEmpty()) {
+    AppendToString(aStream, mHitRegion, " (hitRegion ", ")");
+  }
+  if (!mMaybeHitRegion.IsEmpty()) {
+    AppendToString(aStream, mMaybeHitRegion, " (maybeHitRegion ", ")");
+  }
+  if (!mDispatchToContentHitRegion.IsEmpty()) {
+    AppendToString(aStream, mDispatchToContentHitRegion, " (dispatchToContentRegion ", ")");
+  }
+  if (!mNoActionRegion.IsEmpty()) {
+    AppendToString(aStream, mNoActionRegion, " (noActionRegion ", ")");
+  }
+  if (!mHorizontalPanRegion.IsEmpty()) {
+    AppendToString(aStream, mHorizontalPanRegion, " (horizPanRegion ", ")");
+  }
+  if (!mVerticalPanRegion.IsEmpty()) {
+    AppendToString(aStream, mVerticalPanRegion, " (vertPanRegion ", ")");
+  }
+}
+
+nsDisplayCaret::nsDisplayCaret(nsDisplayListBuilder* aBuilder,
+                               nsIFrame* aCaretFrame)
+  : nsDisplayItem(aBuilder, aCaretFrame)
+  , mCaret(aBuilder->GetCaret())
+  , mBounds(aBuilder->GetCaretRect() + ToReferenceFrame())
+{
+  MOZ_COUNT_CTOR(nsDisplayCaret);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayCaret::~nsDisplayCaret()
+{
+  MOZ_COUNT_DTOR(nsDisplayCaret);
+}
+#endif
+
+nsRect
+nsDisplayCaret::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  *aSnap = true;
+  // The caret returns a rect in the coordinates of mFrame.
+  return mBounds;
+}
+
+void
+nsDisplayCaret::Paint(nsDisplayListBuilder* aBuilder,
+                      nsRenderingContext* aCtx) {
+  // Note: Because we exist, we know that the caret is visible, so we don't
+  // need to check for the caret's visibility.
+  mCaret->PaintCaret(*aCtx->GetDrawTarget(), mFrame, ToReferenceFrame());
+}
+
+nsDisplayBorder::nsDisplayBorder(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+  : nsDisplayItem(aBuilder, aFrame)
+{
+  MOZ_COUNT_CTOR(nsDisplayBorder);
+
+  mBounds = CalculateBounds(*mFrame->StyleBorder());
+}
+
+bool
+nsDisplayBorder::IsInvisibleInRect(const nsRect& aRect)
+{
+  nsRect paddingRect = mFrame->GetPaddingRect() - mFrame->GetPosition() +
+    ToReferenceFrame();
+  const nsStyleBorder *styleBorder;
+  if (paddingRect.Contains(aRect) &&
+      !(styleBorder = mFrame->StyleBorder())->IsBorderImageLoaded() &&
+      !nsLayoutUtils::HasNonZeroCorner(styleBorder->mBorderRadius)) {
+    // aRect is entirely inside the content rect, and no part
+    // of the border is rendered inside the content rect, so we are not
+    // visible
+    // Skip this if there's a border-image (which draws a background
+    // too) or if there is a border-radius (which makes the border draw
+    // further in).
+    return true;
+  }
+
+  return false;
+}
+
+nsDisplayItemGeometry*
+nsDisplayBorder::AllocateGeometry(nsDisplayListBuilder* aBuilder)
+{
+  return new nsDisplayBorderGeometry(this, aBuilder);
+}
+
+void
+nsDisplayBorder::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                           const nsDisplayItemGeometry* aGeometry,
+                                           nsRegion* aInvalidRegion)
+{
+  const nsDisplayBorderGeometry* geometry = static_cast<const nsDisplayBorderGeometry*>(aGeometry);
+  bool snap;
+
+  if (!geometry->mBounds.IsEqualInterior(GetBounds(aBuilder, &snap)) ||
+      !geometry->mContentRect.IsEqualInterior(GetContentRect())) {
+    // We can probably get away with only invalidating the difference
+    // between the border and padding rects, but the XUL ui at least
+    // is apparently painting a background with this?
+    aInvalidRegion->Or(GetBounds(aBuilder, &snap), geometry->mBounds);
+  }
+
+  if (aBuilder->ShouldSyncDecodeImages() &&
+      geometry->ShouldInvalidateToSyncDecodeImages()) {
+    aInvalidRegion->Or(*aInvalidRegion, GetBounds(aBuilder, &snap));
+  }
+}
+
+void
+nsDisplayBorder::Paint(nsDisplayListBuilder* aBuilder,
+                       nsRenderingContext* aCtx) {
+  nsPoint offset = ToReferenceFrame();
+
+  PaintBorderFlags flags = aBuilder->ShouldSyncDecodeImages()
+                         ? PaintBorderFlags::SYNC_DECODE_IMAGES
+                         : PaintBorderFlags();
+
+  image::DrawResult result =
+    nsCSSRendering::PaintBorder(mFrame->PresContext(), *aCtx, mFrame,
+                                mVisibleRect,
+                                nsRect(offset, mFrame->GetSize()),
+                                mFrame->StyleContext(),
+                                flags,
+                                mFrame->GetSkipSides());
+
+  nsDisplayBorderGeometry::UpdateDrawResult(this, result);
+}
+
+nsRect
+nsDisplayBorder::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  *aSnap = true;
+  return mBounds;
+}
+
+nsRect
+nsDisplayBorder::CalculateBounds(const nsStyleBorder& aStyleBorder)
+{
+  nsRect borderBounds(ToReferenceFrame(), mFrame->GetSize());
+  if (aStyleBorder.IsBorderImageLoaded()) {
+    borderBounds.Inflate(aStyleBorder.GetImageOutset());
+    return borderBounds;
+  } else {
+    nsMargin border = aStyleBorder.GetComputedBorder();
+    nsRect result;
+    if (border.top > 0) {
+      result = nsRect(borderBounds.X(), borderBounds.Y(), borderBounds.Width(), border.top);
+    }
+    if (border.right > 0) {
+      result.UnionRect(result, nsRect(borderBounds.XMost() - border.right, borderBounds.Y(), border.right, borderBounds.Height()));
+    }
+    if (border.bottom > 0) {
+      result.UnionRect(result, nsRect(borderBounds.X(), borderBounds.YMost() - border.bottom, borderBounds.Width(), border.bottom));
+    }
+    if (border.left > 0) {
+      result.UnionRect(result, nsRect(borderBounds.X(), borderBounds.Y(), border.left, borderBounds.Height()));
+    }
+
+    nscoord radii[8];
+    if (mFrame->GetBorderRadii(radii)) {
+      if (border.left > 0 || border.top > 0) {
+        nsSize cornerSize(radii[NS_CORNER_TOP_LEFT_X], radii[NS_CORNER_TOP_LEFT_Y]);
+        result.UnionRect(result, nsRect(borderBounds.TopLeft(), cornerSize));
+      }
+      if (border.top > 0 || border.right > 0) {
+        nsSize cornerSize(radii[NS_CORNER_TOP_RIGHT_X], radii[NS_CORNER_TOP_RIGHT_Y]);
+        result.UnionRect(result, nsRect(borderBounds.TopRight() - nsPoint(cornerSize.width, 0), cornerSize));
+      }
+      if (border.right > 0 || border.bottom > 0) {
+        nsSize cornerSize(radii[NS_CORNER_BOTTOM_RIGHT_X], radii[NS_CORNER_BOTTOM_RIGHT_Y]);
+        result.UnionRect(result, nsRect(borderBounds.BottomRight() - nsPoint(cornerSize.width, cornerSize.height), cornerSize));
+      }
+      if (border.bottom > 0 || border.left > 0) {
+        nsSize cornerSize(radii[NS_CORNER_BOTTOM_LEFT_X], radii[NS_CORNER_BOTTOM_LEFT_Y]);
+        result.UnionRect(result, nsRect(borderBounds.BottomLeft() - nsPoint(0, cornerSize.height), cornerSize));
+      }
+    }
+
+    return result;
+  }
+}
+
+// Given a region, compute a conservative approximation to it as a list
+// of rectangles that aren't vertically adjacent (i.e., vertically
+// adjacent or overlapping rectangles are combined).
+// Right now this is only approximate, some vertically overlapping rectangles
+// aren't guaranteed to be combined.
+static void
+ComputeDisjointRectangles(const nsRegion& aRegion,
+                          nsTArray<nsRect>* aRects) {
+  nscoord accumulationMargin = nsPresContext::CSSPixelsToAppUnits(25);
+  nsRect accumulated;
+
+  for (auto iter = aRegion.RectIter(); !iter.Done(); iter.Next()) {
+    const nsRect& r = iter.Get();
+    if (accumulated.IsEmpty()) {
+      accumulated = r;
+      continue;
+    }
+
+    if (accumulated.YMost() >= r.y - accumulationMargin) {
+      accumulated.UnionRect(accumulated, r);
+    } else {
+      aRects->AppendElement(accumulated);
+      accumulated = r;
+    }
+  }
+
+  // Finish the in-flight rectangle, if there is one.
+  if (!accumulated.IsEmpty()) {
+    aRects->AppendElement(accumulated);
+  }
+}
+
+void
+nsDisplayBoxShadowOuter::Paint(nsDisplayListBuilder* aBuilder,
+                               nsRenderingContext* aCtx) {
+  nsPoint offset = ToReferenceFrame();
+  nsRect borderRect = mFrame->VisualBorderRectRelativeToSelf() + offset;
+  nsPresContext* presContext = mFrame->PresContext();
+  AutoTArray<nsRect,10> rects;
+  ComputeDisjointRectangles(mVisibleRegion, &rects);
+
+  PROFILER_LABEL("nsDisplayBoxShadowOuter", "Paint",
+    js::ProfileEntry::Category::GRAPHICS);
+
+  for (uint32_t i = 0; i < rects.Length(); ++i) {
+    nsCSSRendering::PaintBoxShadowOuter(presContext, *aCtx, mFrame,
+                                        borderRect, rects[i], mOpacity);
+  }
+}
+
+nsRect
+nsDisplayBoxShadowOuter::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) {
+  *aSnap = false;
+  return mBounds;
+}
+
+nsRect
+nsDisplayBoxShadowOuter::GetBoundsInternal() {
+  return nsLayoutUtils::GetBoxShadowRectForFrame(mFrame, mFrame->GetSize()) +
+         ToReferenceFrame();
+}
+
+bool
+nsDisplayBoxShadowOuter::IsInvisibleInRect(const nsRect& aRect)
+{
+  nsPoint origin = ToReferenceFrame();
+  nsRect frameRect(origin, mFrame->GetSize());
+  if (!frameRect.Contains(aRect))
+    return false;
+
+  // the visible region is entirely inside the border-rect, and box shadows
+  // never render within the border-rect (unless there's a border radius).
+  nscoord twipsRadii[8];
+  bool hasBorderRadii = mFrame->GetBorderRadii(twipsRadii);
+  if (!hasBorderRadii)
+    return true;
+
+  return RoundedRectContainsRect(frameRect, twipsRadii, aRect);
+}
+
+bool
+nsDisplayBoxShadowOuter::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                           nsRegion* aVisibleRegion) {
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion)) {
+    return false;
+  }
+
+  // Store the actual visible region
+  mVisibleRegion.And(*aVisibleRegion, mVisibleRect);
+  return true;
+}
+
+void
+nsDisplayBoxShadowOuter::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                                   const nsDisplayItemGeometry* aGeometry,
+                                                   nsRegion* aInvalidRegion)
+{
+  const nsDisplayBoxShadowOuterGeometry* geometry =
+    static_cast<const nsDisplayBoxShadowOuterGeometry*>(aGeometry);
+  bool snap;
+  if (!geometry->mBounds.IsEqualInterior(GetBounds(aBuilder, &snap)) ||
+      !geometry->mBorderRect.IsEqualInterior(GetBorderRect()) ||
+      mOpacity != geometry->mOpacity) {
+    nsRegion oldShadow, newShadow;
+    nscoord dontCare[8];
+    bool hasBorderRadius = mFrame->GetBorderRadii(dontCare);
+    if (hasBorderRadius) {
+      // If we have rounded corners then we need to invalidate the frame area
+      // too since we paint into it.
+      oldShadow = geometry->mBounds;
+      newShadow = GetBounds(aBuilder, &snap);
+    } else {
+      oldShadow.Sub(geometry->mBounds, geometry->mBorderRect);
+      newShadow.Sub(GetBounds(aBuilder, &snap), GetBorderRect());
+    }
+    aInvalidRegion->Or(oldShadow, newShadow);
+  }
+}
+
+
+void
+nsDisplayBoxShadowInner::Paint(nsDisplayListBuilder* aBuilder,
+                               nsRenderingContext* aCtx) {
+  nsPoint offset = ToReferenceFrame();
+  nsRect borderRect = nsRect(offset, mFrame->GetSize());
+  nsPresContext* presContext = mFrame->PresContext();
+  AutoTArray<nsRect,10> rects;
+  ComputeDisjointRectangles(mVisibleRegion, &rects);
+
+  PROFILER_LABEL("nsDisplayBoxShadowInner", "Paint",
+    js::ProfileEntry::Category::GRAPHICS);
+
+  DrawTarget* drawTarget = aCtx->GetDrawTarget();
+  gfxContext* gfx = aCtx->ThebesContext();
+  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+
+  for (uint32_t i = 0; i < rects.Length(); ++i) {
+    gfx->Save();
+    gfx->Clip(NSRectToSnappedRect(rects[i], appUnitsPerDevPixel, *drawTarget));
+    nsCSSRendering::PaintBoxShadowInner(presContext, *aCtx, mFrame, borderRect);
+    gfx->Restore();
+  }
+}
+
+bool
+nsDisplayBoxShadowInner::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                           nsRegion* aVisibleRegion) {
+  if (!nsDisplayItem::ComputeVisibility(aBuilder, aVisibleRegion)) {
+    return false;
+  }
+
+  // Store the actual visible region
+  mVisibleRegion.And(*aVisibleRegion, mVisibleRect);
+  return true;
+}
+
+nsDisplayWrapList::nsDisplayWrapList(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame, nsDisplayList* aList)
+  : nsDisplayWrapList(aBuilder, aFrame, aList,
+                      aBuilder->ClipState().GetCurrentInnermostScrollClip())
+{}
+
+nsDisplayWrapList::nsDisplayWrapList(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame, nsDisplayList* aList,
+                                     const DisplayItemScrollClip* aScrollClip)
+  : nsDisplayItem(aBuilder, aFrame, aScrollClip)
+  , mOverrideZIndex(0)
+  , mHasZIndexOverride(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayWrapList);
+
+  mBaseVisibleRect = mVisibleRect;
+
+  mList.AppendToTop(aList);
+  UpdateBounds(aBuilder);
+
+  if (!aFrame || !aFrame->IsTransformed()) {
+    return;
+  }
+
+  // If we're a transformed frame, then we need to find out if we're inside
+  // the nsDisplayTransform or outside of it. Frames inside the transform
+  // need mReferenceFrame == mFrame, outside needs the next ancestor
+  // reference frame.
+  // If we're inside the transform, then the nsDisplayItem constructor
+  // will have done the right thing.
+  // If we're outside the transform, then we should have only one child
+  // (since nsDisplayTransform wraps all actual content), and that child
+  // will have the correct reference frame set (since nsDisplayTransform
+  // handles this explictly).
+  nsDisplayItem *i = mList.GetBottom();
+  if (i && (!i->GetAbove() || i->GetType() == TYPE_TRANSFORM) &&
+      i->Frame() == mFrame) {
+    mReferenceFrame = i->ReferenceFrame();
+    mToReferenceFrame = i->ToReferenceFrame();
+  }
+  mVisibleRect = aBuilder->GetDirtyRect() +
+      aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+}
+
+nsDisplayWrapList::nsDisplayWrapList(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame, nsDisplayItem* aItem)
+  : nsDisplayItem(aBuilder, aFrame)
+  , mOverrideZIndex(0)
+  , mHasZIndexOverride(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayWrapList);
+
+  mBaseVisibleRect = mVisibleRect;
+
+  mList.AppendToTop(aItem);
+  UpdateBounds(aBuilder);
+
+  if (!aFrame || !aFrame->IsTransformed()) {
+    return;
+  }
+
+  // See the previous nsDisplayWrapList constructor
+  if (aItem->Frame() == aFrame) {
+    mReferenceFrame = aItem->ReferenceFrame();
+    mToReferenceFrame = aItem->ToReferenceFrame();
+  }
+  mVisibleRect = aBuilder->GetDirtyRect() +
+      aBuilder->GetCurrentFrameOffsetToReferenceFrame();
+}
+
+nsDisplayWrapList::~nsDisplayWrapList() {
+  mList.DeleteAll();
+
+  MOZ_COUNT_DTOR(nsDisplayWrapList);
+}
+
+void
+nsDisplayWrapList::HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+                           HitTestState* aState, nsTArray<nsIFrame*> *aOutFrames) {
+  mList.HitTest(aBuilder, aRect, aState, aOutFrames);
+}
+
+nsRect
+nsDisplayWrapList::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap) {
+  *aSnap = false;
+  return mBounds;
+}
+
+bool
+nsDisplayWrapList::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                     nsRegion* aVisibleRegion) {
+  // Convert the passed in visible region to our appunits.
+  nsRegion visibleRegion;
+  // mVisibleRect has been clipped to GetClippedBounds
+  visibleRegion.And(*aVisibleRegion, mVisibleRect);
+  nsRegion originalVisibleRegion = visibleRegion;
+
+  bool retval =
+    mList.ComputeVisibilityForSublist(aBuilder, &visibleRegion, mVisibleRect);
+
+  nsRegion removed;
+  // removed = originalVisibleRegion - visibleRegion
+  removed.Sub(originalVisibleRegion, visibleRegion);
+  // aVisibleRegion = aVisibleRegion - removed (modulo any simplifications
+  // SubtractFromVisibleRegion does)
+  aBuilder->SubtractFromVisibleRegion(aVisibleRegion, removed);
+
+  return retval;
+}
+
+nsRegion
+nsDisplayWrapList::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                   bool* aSnap) {
+  *aSnap = false;
+  nsRegion result;
+  if (mList.IsOpaque()) {
+    // Everything within GetBounds that's visible is opaque.
+    result = GetBounds(aBuilder, aSnap);
+  }
+  return result;
+}
+
+Maybe<nscolor>
+nsDisplayWrapList::IsUniform(nsDisplayListBuilder* aBuilder) {
+  // We could try to do something but let's conservatively just return Nothing.
+  return Nothing();
+}
+
+void nsDisplayWrapList::Paint(nsDisplayListBuilder* aBuilder,
+                              nsRenderingContext* aCtx) {
+  NS_ERROR("nsDisplayWrapList should have been flattened away for painting");
+}
+
+/**
+ * Returns true if all descendant display items can be placed in the same
+ * PaintedLayer --- GetLayerState returns LAYER_INACTIVE or LAYER_NONE,
+ * and they all have the expected animated geometry root.
+ */
+static LayerState
+RequiredLayerStateForChildren(nsDisplayListBuilder* aBuilder,
+                              LayerManager* aManager,
+                              const ContainerLayerParameters& aParameters,
+                              const nsDisplayList& aList,
+                              AnimatedGeometryRoot* aExpectedAnimatedGeometryRootForChildren)
+{
+  LayerState result = LAYER_INACTIVE;
+  for (nsDisplayItem* i = aList.GetBottom(); i; i = i->GetAbove()) {
+    if (result == LAYER_INACTIVE &&
+        i->GetAnimatedGeometryRoot() != aExpectedAnimatedGeometryRootForChildren) {
+      result = LAYER_ACTIVE;
+    }
+
+    LayerState state = i->GetLayerState(aBuilder, aManager, aParameters);
+    if (state == LAYER_ACTIVE && i->GetType() == nsDisplayItem::TYPE_BLEND_MODE) {
+      // nsDisplayBlendMode always returns LAYER_ACTIVE to ensure that the
+      // blending operation happens in the intermediate surface of its parent
+      // display item (usually an nsDisplayBlendContainer). But this does not
+      // mean that it needs all its ancestor display items to become active.
+      // So we ignore its layer state and look at its children instead.
+      state = RequiredLayerStateForChildren(aBuilder, aManager, aParameters,
+        *i->GetSameCoordinateSystemChildren(), i->GetAnimatedGeometryRoot());
+    }
+    if ((state == LAYER_ACTIVE || state == LAYER_ACTIVE_FORCE) &&
+        state > result) {
+      result = state;
+    }
+    if (state == LAYER_ACTIVE_EMPTY && state > result) {
+      result = LAYER_ACTIVE_FORCE;
+    }
+    if (state == LAYER_NONE) {
+      nsDisplayList* list = i->GetSameCoordinateSystemChildren();
+      if (list) {
+        LayerState childState =
+          RequiredLayerStateForChildren(aBuilder, aManager, aParameters, *list,
+              aExpectedAnimatedGeometryRootForChildren);
+        if (childState > result) {
+          result = childState;
+        }
+      }
+    }
+  }
+  return result;
+}
+
+nsRect nsDisplayWrapList::GetComponentAlphaBounds(nsDisplayListBuilder* aBuilder)
+{
+  nsRect bounds;
+  for (nsDisplayItem* i = mList.GetBottom(); i; i = i->GetAbove()) {
+    bounds.UnionRect(bounds, i->GetComponentAlphaBounds(aBuilder));
+  }
+  return bounds;
+}
+
+void
+nsDisplayWrapList::SetVisibleRect(const nsRect& aRect)
+{
+  mVisibleRect = aRect;
+}
+
+void
+nsDisplayWrapList::SetReferenceFrame(const nsIFrame* aFrame)
+{
+  mReferenceFrame = aFrame;
+  mToReferenceFrame = mFrame->GetOffsetToCrossDoc(mReferenceFrame);
+}
+
+static nsresult
+WrapDisplayList(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                nsDisplayList* aList, nsDisplayWrapper* aWrapper) {
+  if (!aList->GetTop())
+    return NS_OK;
+  nsDisplayItem* item = aWrapper->WrapList(aBuilder, aFrame, aList);
+  if (!item)
+    return NS_ERROR_OUT_OF_MEMORY;
+  // aList was emptied
+  aList->AppendToTop(item);
+  return NS_OK;
+}
+
+static nsresult
+WrapEachDisplayItem(nsDisplayListBuilder* aBuilder,
+                    nsDisplayList* aList, nsDisplayWrapper* aWrapper) {
+  nsDisplayList newList;
+  nsDisplayItem* item;
+  while ((item = aList->RemoveBottom())) {
+    item = aWrapper->WrapItem(aBuilder, item);
+    if (!item)
+      return NS_ERROR_OUT_OF_MEMORY;
+    newList.AppendToTop(item);
+  }
+  // aList was emptied
+  aList->AppendToTop(&newList);
+  return NS_OK;
+}
+
+nsresult nsDisplayWrapper::WrapLists(nsDisplayListBuilder* aBuilder,
+    nsIFrame* aFrame, const nsDisplayListSet& aIn, const nsDisplayListSet& aOut)
+{
+  nsresult rv = WrapListsInPlace(aBuilder, aFrame, aIn);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (&aOut == &aIn)
+    return NS_OK;
+  aOut.BorderBackground()->AppendToTop(aIn.BorderBackground());
+  aOut.BlockBorderBackgrounds()->AppendToTop(aIn.BlockBorderBackgrounds());
+  aOut.Floats()->AppendToTop(aIn.Floats());
+  aOut.Content()->AppendToTop(aIn.Content());
+  aOut.PositionedDescendants()->AppendToTop(aIn.PositionedDescendants());
+  aOut.Outlines()->AppendToTop(aIn.Outlines());
+  return NS_OK;
+}
+
+nsresult nsDisplayWrapper::WrapListsInPlace(nsDisplayListBuilder* aBuilder,
+    nsIFrame* aFrame, const nsDisplayListSet& aLists)
+{
+  nsresult rv;
+  if (WrapBorderBackground()) {
+    // Our border-backgrounds are in-flow
+    rv = WrapDisplayList(aBuilder, aFrame, aLists.BorderBackground(), this);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  // Our block border-backgrounds are in-flow
+  rv = WrapDisplayList(aBuilder, aFrame, aLists.BlockBorderBackgrounds(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // The floats are not in flow
+  rv = WrapEachDisplayItem(aBuilder, aLists.Floats(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // Our child content is in flow
+  rv = WrapDisplayList(aBuilder, aFrame, aLists.Content(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // The positioned descendants may not be in-flow
+  rv = WrapEachDisplayItem(aBuilder, aLists.PositionedDescendants(), this);
+  NS_ENSURE_SUCCESS(rv, rv);
+  // The outlines may not be in-flow
+  return WrapEachDisplayItem(aBuilder, aLists.Outlines(), this);
+}
+
+nsDisplayOpacity::nsDisplayOpacity(nsDisplayListBuilder* aBuilder,
+                                   nsIFrame* aFrame, nsDisplayList* aList,
+                                   const DisplayItemScrollClip* aScrollClip,
+                                   bool aForEventsAndPluginsOnly)
+    : nsDisplayWrapList(aBuilder, aFrame, aList, aScrollClip)
+    , mOpacity(aFrame->StyleEffects()->mOpacity)
+    , mForEventsAndPluginsOnly(aForEventsAndPluginsOnly)
+{
+  MOZ_COUNT_CTOR(nsDisplayOpacity);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayOpacity::~nsDisplayOpacity() {
+  MOZ_COUNT_DTOR(nsDisplayOpacity);
+}
+#endif
+
+nsRegion nsDisplayOpacity::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                           bool* aSnap) {
+  *aSnap = false;
+  // The only time where mOpacity == 1.0 should be when we have will-change.
+  // We could report this as opaque then but when the will-change value starts
+  // animating the element would become non opaque and could cause repaints.
+  return nsRegion();
+}
+
+// nsDisplayOpacity uses layers for rendering
+already_AddRefed<Layer>
+nsDisplayOpacity::BuildLayer(nsDisplayListBuilder* aBuilder,
+                             LayerManager* aManager,
+                             const ContainerLayerParameters& aContainerParameters) {
+  ContainerLayerParameters params = aContainerParameters;
+  params.mForEventsAndPluginsOnly = mForEventsAndPluginsOnly;
+  RefPtr<Layer> container = aManager->GetLayerBuilder()->
+    BuildContainerLayerFor(aBuilder, aManager, mFrame, this, &mList,
+                           params, nullptr,
+                           FrameLayerBuilder::CONTAINER_ALLOW_PULL_BACKGROUND_COLOR);
+  if (!container)
+    return nullptr;
+
+  container->SetOpacity(mOpacity);
+  nsDisplayListBuilder::AddAnimationsAndTransitionsToLayer(container, aBuilder,
+                                                           this, mFrame,
+                                                           eCSSProperty_opacity);
+  return container.forget();
+}
+
+/**
+ * This doesn't take into account layer scaling --- the layer may be
+ * rendered at a higher (or lower) resolution, affecting the retained layer
+ * size --- but this should be good enough.
+ */
+static bool
+IsItemTooSmallForActiveLayer(nsIFrame* aFrame)
+{
+  nsIntRect visibleDevPixels = aFrame->GetVisualOverflowRectRelativeToSelf().ToOutsidePixels(
+          aFrame->PresContext()->AppUnitsPerDevPixel());
+  static const int MIN_ACTIVE_LAYER_SIZE_DEV_PIXELS = 16;
+  return visibleDevPixels.Size() <
+    nsIntSize(MIN_ACTIVE_LAYER_SIZE_DEV_PIXELS, MIN_ACTIVE_LAYER_SIZE_DEV_PIXELS);
+}
+
+static void
+SetAnimationPerformanceWarningForTooSmallItem(nsIFrame* aFrame,
+                                              nsCSSPropertyID aProperty)
+{
+  // We use ToNearestPixels() here since ToOutsidePixels causes some sort of
+  // errors. See https://bugzilla.mozilla.org/show_bug.cgi?id=1258904#c19
+  nsIntRect visibleDevPixels = aFrame->GetVisualOverflowRectRelativeToSelf().ToNearestPixels(
+          aFrame->PresContext()->AppUnitsPerDevPixel());
+
+  // Set performance warning only if the visible dev pixels is not empty
+  // because dev pixels is empty if the frame has 'preserve-3d' style.
+  if (visibleDevPixels.IsEmpty()) {
+    return;
+  }
+
+  EffectCompositor::SetPerformanceWarning(aFrame, aProperty,
+      AnimationPerformanceWarning(
+        AnimationPerformanceWarning::Type::ContentTooSmall,
+        { visibleDevPixels.Width(), visibleDevPixels.Height() }));
+}
+
+/* static */ bool
+nsDisplayOpacity::NeedsActiveLayer(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+{
+  if (ActiveLayerTracker::IsStyleAnimated(aBuilder, aFrame,
+                                          eCSSProperty_opacity) ||
+      EffectCompositor::HasAnimationsForCompositor(aFrame,
+                                                   eCSSProperty_opacity)) {
+    if (!IsItemTooSmallForActiveLayer(aFrame)) {
+      return true;
+    }
+    SetAnimationPerformanceWarningForTooSmallItem(aFrame, eCSSProperty_opacity);
+  }
+  return false;
+}
+
+void
+nsDisplayOpacity::ApplyOpacity(nsDisplayListBuilder* aBuilder,
+                             float aOpacity,
+                             const DisplayItemClip* aClip)
+{
+  NS_ASSERTION(CanApplyOpacity(), "ApplyOpacity should be allowed");
+  mOpacity = mOpacity * aOpacity;
+  if (aClip) {
+    IntersectClip(aBuilder, *aClip);
+  }
+}
+
+bool
+nsDisplayOpacity::CanApplyOpacity() const
+{
+  return true;
+}
+
+bool
+nsDisplayOpacity::ShouldFlattenAway(nsDisplayListBuilder* aBuilder)
+{
+  if (NeedsActiveLayer(aBuilder, mFrame) || mOpacity == 0.0) {
+    // If our opacity is zero then we'll discard all descendant display items
+    // except for layer event regions, so there's no point in doing this
+    // optimization (and if we do do it, then invalidations of those descendants
+    // might trigger repainting).
+    return false;
+  }
+
+  nsDisplayItem* child = mList.GetBottom();
+  // Only try folding our opacity down if we have at most three children
+  // that don't overlap and can all apply the opacity to themselves.
+  if (!child) {
+    return false;
+  }
+  struct {
+    nsDisplayItem* item;
+    nsRect bounds;
+  } children[3];
+  bool snap;
+  uint32_t numChildren = 0;
+  for (; numChildren < ArrayLength(children) && child; numChildren++, child = child->GetAbove()) {
+    if (child->GetType() == nsDisplayItem::TYPE_LAYER_EVENT_REGIONS) {
+      numChildren--;
+      continue;
+    }
+    if (!child->CanApplyOpacity()) {
+      return false;
+    }
+    children[numChildren].item = child;
+    children[numChildren].bounds = child->GetBounds(aBuilder, &snap);
+  }
+  if (child) {
+    // we have a fourth (or more) child
+    return false;
+  }
+
+  for (uint32_t i = 0; i < numChildren; i++) {
+    for (uint32_t j = i+1; j < numChildren; j++) {
+      if (children[i].bounds.Intersects(children[j].bounds)) {
+        return false;
+      }
+    }
+  }
+
+  for (uint32_t i = 0; i < numChildren; i++) {
+    children[i].item->ApplyOpacity(aBuilder, mOpacity, mClip);
+  }
+  return true;
+}
+
+nsDisplayItem::LayerState
+nsDisplayOpacity::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                LayerManager* aManager,
+                                const ContainerLayerParameters& aParameters) {
+  // If we only created this item so that we'd get correct nsDisplayEventRegions for child
+  // frames, then force us to inactive to avoid unnecessary layerization changes for content
+  // that won't ever be painted.
+  if (mForEventsAndPluginsOnly) {
+    MOZ_ASSERT(mOpacity == 0);
+    return LAYER_INACTIVE;
+  }
+
+  if (NeedsActiveLayer(aBuilder, mFrame)) {
+    // Returns LAYER_ACTIVE_FORCE to avoid flatterning the layer for async
+    // animations.
+    return LAYER_ACTIVE_FORCE;
+  }
+
+  return RequiredLayerStateForChildren(aBuilder, aManager, aParameters, mList, GetAnimatedGeometryRoot());
+}
+
+bool
+nsDisplayOpacity::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                    nsRegion* aVisibleRegion) {
+  // Our children are translucent so we should not allow them to subtract
+  // area from aVisibleRegion. We do need to find out what is visible under
+  // our children in the temporary compositing buffer, because if our children
+  // paint our entire bounds opaquely then we don't need an alpha channel in
+  // the temporary compositing buffer.
+  nsRect bounds = GetClippedBounds(aBuilder);
+  nsRegion visibleUnderChildren;
+  visibleUnderChildren.And(*aVisibleRegion, bounds);
+  return
+    nsDisplayWrapList::ComputeVisibility(aBuilder, &visibleUnderChildren);
+}
+
+bool nsDisplayOpacity::TryMerge(nsDisplayItem* aItem) {
+  if (aItem->GetType() != TYPE_OPACITY)
+    return false;
+  // items for the same content element should be merged into a single
+  // compositing group
+  // aItem->GetUnderlyingFrame() returns non-null because it's nsDisplayOpacity
+  if (aItem->Frame()->GetContent() != mFrame->GetContent())
+    return false;
+  if (aItem->GetClip() != GetClip())
+    return false;
+  if (aItem->ScrollClip() != ScrollClip())
+    return false;
+  MergeFromTrackingMergedFrames(static_cast<nsDisplayOpacity*>(aItem));
+  return true;
+}
+
+void
+nsDisplayOpacity::WriteDebugInfo(std::stringstream& aStream)
+{
+  aStream << " (opacity " << mOpacity << ")";
+}
+
+nsDisplayBlendMode::nsDisplayBlendMode(nsDisplayListBuilder* aBuilder,
+                                             nsIFrame* aFrame, nsDisplayList* aList,
+                                             uint8_t aBlendMode,
+                                             const DisplayItemScrollClip* aScrollClip,
+                                             uint32_t aIndex)
+  : nsDisplayWrapList(aBuilder, aFrame, aList, aScrollClip)
+  , mBlendMode(aBlendMode)
+  , mIndex(aIndex)
+{
+  MOZ_COUNT_CTOR(nsDisplayBlendMode);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayBlendMode::~nsDisplayBlendMode() {
+  MOZ_COUNT_DTOR(nsDisplayBlendMode);
+}
+#endif
+
+nsRegion nsDisplayBlendMode::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                                bool* aSnap) {
+  *aSnap = false;
+  // We are never considered opaque
+  return nsRegion();
+}
+
+LayerState
+nsDisplayBlendMode::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                     LayerManager* aManager,
+                                     const ContainerLayerParameters& aParameters)
+{
+  return LAYER_ACTIVE;
+}
+
+// nsDisplayBlendMode uses layers for rendering
+already_AddRefed<Layer>
+nsDisplayBlendMode::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                  LayerManager* aManager,
+                                  const ContainerLayerParameters& aContainerParameters) {
+  ContainerLayerParameters newContainerParameters = aContainerParameters;
+  newContainerParameters.mDisableSubpixelAntialiasingInDescendants = true;
+
+  RefPtr<Layer> container = aManager->GetLayerBuilder()->
+  BuildContainerLayerFor(aBuilder, aManager, mFrame, this, &mList,
+                         newContainerParameters, nullptr);
+  if (!container) {
+    return nullptr;
+  }
+
+  container->SetMixBlendMode(nsCSSRendering::GetGFXBlendMode(mBlendMode));
+
+  return container.forget();
+}
+
+bool nsDisplayBlendMode::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                              nsRegion* aVisibleRegion) {
+  // Our children are need their backdrop so we should not allow them to subtract
+  // area from aVisibleRegion. We do need to find out what is visible under
+  // our children in the temporary compositing buffer, because if our children
+  // paint our entire bounds opaquely then we don't need an alpha channel in
+  // the temporary compositing buffer.
+  nsRect bounds = GetClippedBounds(aBuilder);
+  nsRegion visibleUnderChildren;
+  visibleUnderChildren.And(*aVisibleRegion, bounds);
+  return nsDisplayWrapList::ComputeVisibility(aBuilder, &visibleUnderChildren);
+}
+
+bool nsDisplayBlendMode::TryMerge(nsDisplayItem* aItem) {
+  if (aItem->GetType() != TYPE_BLEND_MODE)
+    return false;
+  nsDisplayBlendMode* item = static_cast<nsDisplayBlendMode*>(aItem);
+  // items for the same content element should be merged into a single
+  // compositing group
+  if (item->Frame()->GetContent() != mFrame->GetContent())
+    return false;
+  if (item->mIndex != 0 || mIndex != 0)
+    return false; // don't merge background-blend-mode items
+  if (item->GetClip() != GetClip())
+    return false;
+  if (item->ScrollClip() != ScrollClip())
+    return false;
+  MergeFromTrackingMergedFrames(item);
+  return true;
+}
+
+/* static */ nsDisplayBlendContainer*
+nsDisplayBlendContainer::CreateForMixBlendMode(nsDisplayListBuilder* aBuilder,
+                                               nsIFrame* aFrame, nsDisplayList* aList,
+                                               const DisplayItemScrollClip* aScrollClip)
+{
+  return new (aBuilder) nsDisplayBlendContainer(aBuilder, aFrame, aList, aScrollClip, false);
+}
+
+/* static */ nsDisplayBlendContainer*
+nsDisplayBlendContainer::CreateForBackgroundBlendMode(nsDisplayListBuilder* aBuilder,
+                                                      nsIFrame* aFrame, nsDisplayList* aList,
+                                                      const DisplayItemScrollClip* aScrollClip)
+{
+  return new (aBuilder) nsDisplayBlendContainer(aBuilder, aFrame, aList, aScrollClip, true);
+}
+
+nsDisplayBlendContainer::nsDisplayBlendContainer(nsDisplayListBuilder* aBuilder,
+                                                 nsIFrame* aFrame, nsDisplayList* aList,
+                                                 const DisplayItemScrollClip* aScrollClip,
+                                                 bool aIsForBackground)
+    : nsDisplayWrapList(aBuilder, aFrame, aList, aScrollClip)
+    , mIsForBackground(aIsForBackground)
+{
+  MOZ_COUNT_CTOR(nsDisplayBlendContainer);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayBlendContainer::~nsDisplayBlendContainer() {
+  MOZ_COUNT_DTOR(nsDisplayBlendContainer);
+}
+#endif
+
+// nsDisplayBlendContainer uses layers for rendering
+already_AddRefed<Layer>
+nsDisplayBlendContainer::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                    LayerManager* aManager,
+                                    const ContainerLayerParameters& aContainerParameters) {
+  // turn off anti-aliasing in the parent stacking context because it changes
+  // how the group is initialized.
+  ContainerLayerParameters newContainerParameters = aContainerParameters;
+  newContainerParameters.mDisableSubpixelAntialiasingInDescendants = true;
+
+  RefPtr<Layer> container = aManager->GetLayerBuilder()->
+  BuildContainerLayerFor(aBuilder, aManager, mFrame, this, &mList,
+                         newContainerParameters, nullptr);
+  if (!container) {
+    return nullptr;
+  }
+
+  container->SetForceIsolatedGroup(true);
+  return container.forget();
+}
+
+LayerState
+nsDisplayBlendContainer::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                       LayerManager* aManager,
+                                       const ContainerLayerParameters& aParameters)
+{
+  return RequiredLayerStateForChildren(aBuilder, aManager, aParameters, mList, GetAnimatedGeometryRoot());
+}
+
+bool nsDisplayBlendContainer::TryMerge(nsDisplayItem* aItem) {
+  if (aItem->GetType() != TYPE_BLEND_CONTAINER)
+    return false;
+  // items for the same content element should be merged into a single
+  // compositing group
+  // aItem->GetUnderlyingFrame() returns non-null because it's nsDisplayOpacity
+  if (aItem->Frame()->GetContent() != mFrame->GetContent())
+    return false;
+  if (aItem->GetClip() != GetClip())
+    return false;
+  if (aItem->ScrollClip() != ScrollClip())
+    return false;
+  MergeFromTrackingMergedFrames(static_cast<nsDisplayBlendContainer*>(aItem));
+  return true;
+}
+
+nsDisplayOwnLayer::nsDisplayOwnLayer(nsDisplayListBuilder* aBuilder,
+                                     nsIFrame* aFrame, nsDisplayList* aList,
+                                     uint32_t aFlags, ViewID aScrollTarget,
+                                     float aScrollbarThumbRatio,
+                                     bool aForceActive)
+    : nsDisplayWrapList(aBuilder, aFrame, aList)
+    , mFlags(aFlags)
+    , mScrollTarget(aScrollTarget)
+    , mScrollbarThumbRatio(aScrollbarThumbRatio)
+    , mForceActive(aForceActive)
+{
+  MOZ_COUNT_CTOR(nsDisplayOwnLayer);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayOwnLayer::~nsDisplayOwnLayer() {
+  MOZ_COUNT_DTOR(nsDisplayOwnLayer);
+}
+#endif
+
+LayerState
+nsDisplayOwnLayer::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                 LayerManager* aManager,
+                                 const ContainerLayerParameters& aParameters)
+{
+  if (mForceActive) {
+    return mozilla::LAYER_ACTIVE_FORCE;
+  }
+
+  return RequiredLayerStateForChildren(aBuilder, aManager, aParameters, mList, mAnimatedGeometryRoot);
+}
+
+// nsDisplayOpacity uses layers for rendering
+already_AddRefed<Layer>
+nsDisplayOwnLayer::BuildLayer(nsDisplayListBuilder* aBuilder,
+                              LayerManager* aManager,
+                              const ContainerLayerParameters& aContainerParameters)
+{
+  RefPtr<ContainerLayer> layer = aManager->GetLayerBuilder()->
+    BuildContainerLayerFor(aBuilder, aManager, mFrame, this, &mList,
+                           aContainerParameters, nullptr,
+                           FrameLayerBuilder::CONTAINER_ALLOW_PULL_BACKGROUND_COLOR);
+  if (mFlags & VERTICAL_SCROLLBAR) {
+    layer->SetScrollbarData(mScrollTarget, Layer::ScrollDirection::VERTICAL, mScrollbarThumbRatio);
+  }
+  if (mFlags & HORIZONTAL_SCROLLBAR) {
+    layer->SetScrollbarData(mScrollTarget, Layer::ScrollDirection::HORIZONTAL, mScrollbarThumbRatio);
+  }
+  if (mFlags & SCROLLBAR_CONTAINER) {
+    layer->SetIsScrollbarContainer();
+  }
+
+  if (mFlags & GENERATE_SUBDOC_INVALIDATIONS) {
+    mFrame->PresContext()->SetNotifySubDocInvalidationData(layer);
+  }
+  return layer.forget();
+}
+
+nsDisplaySubDocument::nsDisplaySubDocument(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aFrame, nsDisplayList* aList,
+                                           uint32_t aFlags)
+    : nsDisplayOwnLayer(aBuilder, aFrame, aList, aFlags)
+    , mScrollParentId(aBuilder->GetCurrentScrollParentId())
+{
+  MOZ_COUNT_CTOR(nsDisplaySubDocument);
+  mForceDispatchToContentRegion =
+    aBuilder->IsBuildingLayerEventRegions() &&
+    nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(aFrame->PresContext()->PresShell());
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplaySubDocument::~nsDisplaySubDocument() {
+  MOZ_COUNT_DTOR(nsDisplaySubDocument);
+}
+#endif
+
+already_AddRefed<Layer>
+nsDisplaySubDocument::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                 LayerManager* aManager,
+                                 const ContainerLayerParameters& aContainerParameters) {
+  nsPresContext* presContext = mFrame->PresContext();
+  nsIFrame* rootScrollFrame = presContext->PresShell()->GetRootScrollFrame();
+  ContainerLayerParameters params = aContainerParameters;
+  if ((mFlags & GENERATE_SCROLLABLE_LAYER) &&
+      rootScrollFrame->GetContent() &&
+      nsLayoutUtils::HasCriticalDisplayPort(rootScrollFrame->GetContent())) {
+    params.mInLowPrecisionDisplayPort = true;
+  }
+
+  RefPtr<Layer> layer = nsDisplayOwnLayer::BuildLayer(aBuilder, aManager, params);
+  layer->AsContainerLayer()->SetEventRegionsOverride(mForceDispatchToContentRegion
+    ? EventRegionsOverride::ForceDispatchToContent
+    : EventRegionsOverride::NoOverride);
+  return layer.forget();
+}
+
+UniquePtr<ScrollMetadata>
+nsDisplaySubDocument::ComputeScrollMetadata(Layer* aLayer,
+                                            const ContainerLayerParameters& aContainerParameters)
+{
+  if (!(mFlags & GENERATE_SCROLLABLE_LAYER)) {
+    return UniquePtr<ScrollMetadata>(nullptr);
+  }
+
+  nsPresContext* presContext = mFrame->PresContext();
+  nsIFrame* rootScrollFrame = presContext->PresShell()->GetRootScrollFrame();
+  bool isRootContentDocument = presContext->IsRootContentDocument();
+  nsIPresShell* presShell = presContext->PresShell();
+  ContainerLayerParameters params(
+      aContainerParameters.mXScale * presShell->GetResolution(),
+      aContainerParameters.mYScale * presShell->GetResolution(),
+      nsIntPoint(), aContainerParameters);
+  if ((mFlags & GENERATE_SCROLLABLE_LAYER) &&
+      rootScrollFrame->GetContent() &&
+      nsLayoutUtils::HasCriticalDisplayPort(rootScrollFrame->GetContent())) {
+    params.mInLowPrecisionDisplayPort = true;
+  }
+
+  nsRect viewport = mFrame->GetRect() -
+                    mFrame->GetPosition() +
+                    mFrame->GetOffsetToCrossDoc(ReferenceFrame());
+
+  return MakeUnique<ScrollMetadata>(
+    nsLayoutUtils::ComputeScrollMetadata(
+      mFrame, rootScrollFrame, rootScrollFrame->GetContent(), ReferenceFrame(),
+      aLayer, mScrollParentId, viewport, Nothing(),
+      isRootContentDocument, params));
+}
+
+static bool
+UseDisplayPortForViewport(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+{
+  return aBuilder->IsPaintingToWindow() &&
+      nsLayoutUtils::ViewportHasDisplayPort(aFrame->PresContext());
+}
+
+nsRect
+nsDisplaySubDocument::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  bool usingDisplayPort = UseDisplayPortForViewport(aBuilder, mFrame);
+
+  if ((mFlags & GENERATE_SCROLLABLE_LAYER) && usingDisplayPort) {
+    *aSnap = false;
+    return mFrame->GetRect() + aBuilder->ToReferenceFrame(mFrame);
+  }
+
+  return nsDisplayOwnLayer::GetBounds(aBuilder, aSnap);
+}
+
+bool
+nsDisplaySubDocument::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                        nsRegion* aVisibleRegion)
+{
+  bool usingDisplayPort = UseDisplayPortForViewport(aBuilder, mFrame);
+
+  if (!(mFlags & GENERATE_SCROLLABLE_LAYER) || !usingDisplayPort) {
+    return nsDisplayWrapList::ComputeVisibility(aBuilder, aVisibleRegion);
+  }
+
+  nsRect displayport;
+  nsIFrame* rootScrollFrame = mFrame->PresContext()->PresShell()->GetRootScrollFrame();
+  MOZ_ASSERT(rootScrollFrame);
+  Unused << nsLayoutUtils::GetDisplayPort(rootScrollFrame->GetContent(), &displayport,
+    RelativeTo::ScrollFrame);
+
+  nsRegion childVisibleRegion;
+  // The visible region for the children may be much bigger than the hole we
+  // are viewing the children from, so that the compositor process has enough
+  // content to asynchronously pan while content is being refreshed.
+  childVisibleRegion = displayport + mFrame->GetOffsetToCrossDoc(ReferenceFrame());
+
+  nsRect boundedRect =
+    childVisibleRegion.GetBounds().Intersect(mList.GetBounds(aBuilder));
+  bool visible = mList.ComputeVisibilityForSublist(
+    aBuilder, &childVisibleRegion, boundedRect);
+
+  // If APZ is enabled then don't allow this computation to influence
+  // aVisibleRegion, on the assumption that the layer can be asynchronously
+  // scrolled so we'll definitely need all the content under it.
+  if (!nsLayoutUtils::UsesAsyncScrolling(mFrame)) {
+    bool snap;
+    nsRect bounds = GetBounds(aBuilder, &snap);
+    nsRegion removed;
+    removed.Sub(bounds, childVisibleRegion);
+
+    aBuilder->SubtractFromVisibleRegion(aVisibleRegion, removed);
+  }
+
+  return visible;
+}
+
+bool
+nsDisplaySubDocument::ShouldBuildLayerEvenIfInvisible(nsDisplayListBuilder* aBuilder)
+{
+  bool usingDisplayPort = UseDisplayPortForViewport(aBuilder, mFrame);
+
+  if ((mFlags & GENERATE_SCROLLABLE_LAYER) && usingDisplayPort) {
+    return true;
+  }
+
+  return nsDisplayOwnLayer::ShouldBuildLayerEvenIfInvisible(aBuilder);
+}
+
+nsRegion
+nsDisplaySubDocument::GetOpaqueRegion(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  bool usingDisplayPort = UseDisplayPortForViewport(aBuilder, mFrame);
+
+  if ((mFlags & GENERATE_SCROLLABLE_LAYER) && usingDisplayPort) {
+    *aSnap = false;
+    return nsRegion();
+  }
+
+  return nsDisplayOwnLayer::GetOpaqueRegion(aBuilder, aSnap);
+}
+
+nsDisplayResolution::nsDisplayResolution(nsDisplayListBuilder* aBuilder,
+                                         nsIFrame* aFrame, nsDisplayList* aList,
+                                         uint32_t aFlags)
+    : nsDisplaySubDocument(aBuilder, aFrame, aList, aFlags) {
+  MOZ_COUNT_CTOR(nsDisplayResolution);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayResolution::~nsDisplayResolution() {
+  MOZ_COUNT_DTOR(nsDisplayResolution);
+}
+#endif
+
+void
+nsDisplayResolution::HitTest(nsDisplayListBuilder* aBuilder,
+                             const nsRect& aRect,
+                             HitTestState* aState,
+                             nsTArray<nsIFrame*> *aOutFrames)
+{
+  nsIPresShell* presShell = mFrame->PresContext()->PresShell();
+  nsRect rect = aRect.RemoveResolution(presShell->ScaleToResolution() ? presShell->GetResolution () : 1.0f);
+  mList.HitTest(aBuilder, rect, aState, aOutFrames);
+}
+
+already_AddRefed<Layer>
+nsDisplayResolution::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                LayerManager* aManager,
+                                const ContainerLayerParameters& aContainerParameters) {
+  nsIPresShell* presShell = mFrame->PresContext()->PresShell();
+  ContainerLayerParameters containerParameters(
+    presShell->GetResolution(), presShell->GetResolution(), nsIntPoint(),
+    aContainerParameters);
+
+  RefPtr<Layer> layer = nsDisplaySubDocument::BuildLayer(
+    aBuilder, aManager, containerParameters);
+  layer->SetPostScale(1.0f / presShell->GetResolution(),
+                      1.0f / presShell->GetResolution());
+  layer->AsContainerLayer()->SetScaleToResolution(
+      presShell->ScaleToResolution(), presShell->GetResolution());
+  return layer.forget();
+}
+
+nsDisplayFixedPosition::nsDisplayFixedPosition(nsDisplayListBuilder* aBuilder,
+                                               nsIFrame* aFrame,
+                                               nsDisplayList* aList)
+  : nsDisplayOwnLayer(aBuilder, aFrame, aList)
+  , mIndex(0)
+  , mIsFixedBackground(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayFixedPosition);
+  Init(aBuilder);
+}
+
+nsDisplayFixedPosition::nsDisplayFixedPosition(nsDisplayListBuilder* aBuilder,
+                                               nsIFrame* aFrame,
+                                               nsDisplayList* aList,
+                                               uint32_t aIndex)
+  : nsDisplayOwnLayer(aBuilder, aFrame, aList)
+  , mIndex(aIndex)
+  , mIsFixedBackground(true)
+{
+  MOZ_COUNT_CTOR(nsDisplayFixedPosition);
+  Init(aBuilder);
+}
+
+void
+nsDisplayFixedPosition::Init(nsDisplayListBuilder* aBuilder)
+{
+  mAnimatedGeometryRootForScrollMetadata = mAnimatedGeometryRoot;
+  if (ShouldFixToViewport(aBuilder)) {
+    mAnimatedGeometryRoot = aBuilder->FindAnimatedGeometryRootFor(this);
+  }
+}
+
+/* static */ nsDisplayFixedPosition*
+nsDisplayFixedPosition::CreateForFixedBackground(nsDisplayListBuilder* aBuilder,
+                                                 nsIFrame* aFrame,
+                                                 nsDisplayBackgroundImage* aImage,
+                                                 uint32_t aIndex)
+{
+  // Clear clipping on the child item, since we will apply it to the
+  // fixed position item as well.
+  aImage->SetClip(aBuilder, DisplayItemClip());
+  aImage->SetScrollClip(nullptr);
+
+  nsDisplayList temp;
+  temp.AppendToTop(aImage);
+
+  return new (aBuilder) nsDisplayFixedPosition(aBuilder, aFrame, &temp, aIndex + 1);
+}
+
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayFixedPosition::~nsDisplayFixedPosition() {
+  MOZ_COUNT_DTOR(nsDisplayFixedPosition);
+}
+#endif
+
+already_AddRefed<Layer>
+nsDisplayFixedPosition::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                   LayerManager* aManager,
+                                   const ContainerLayerParameters& aContainerParameters) {
+  RefPtr<Layer> layer =
+    nsDisplayOwnLayer::BuildLayer(aBuilder, aManager, aContainerParameters);
+
+  layer->SetIsFixedPosition(true);
+
+  nsPresContext* presContext = mFrame->PresContext();
+  nsIFrame* fixedFrame = mIsFixedBackground ? presContext->PresShell()->GetRootFrame() : mFrame;
+
+  const nsIFrame* viewportFrame = fixedFrame->GetParent();
+  // anchorRect will be in the container's coordinate system (aLayer's parent layer).
+  // This is the same as the display items' reference frame.
+  nsRect anchorRect;
+  if (viewportFrame) {
+    // Fixed position frames are reflowed into the scroll-port size if one has
+    // been set.
+    if (presContext->PresShell()->IsScrollPositionClampingScrollPortSizeSet()) {
+      anchorRect.SizeTo(presContext->PresShell()->GetScrollPositionClampingScrollPortSize());
+    } else {
+      anchorRect.SizeTo(viewportFrame->GetSize());
+    }
+  } else {
+    // A display item directly attached to the viewport.
+    // For background-attachment:fixed items, the anchor point is always the
+    // top-left of the viewport currently.
+    viewportFrame = fixedFrame;
+  }
+  // The anchorRect top-left is always the viewport top-left.
+  anchorRect.MoveTo(viewportFrame->GetOffsetToCrossDoc(ReferenceFrame()));
+
+  nsLayoutUtils::SetFixedPositionLayerData(layer,
+      viewportFrame, anchorRect, fixedFrame, presContext, aContainerParameters);
+
+  return layer.forget();
+}
+
+bool nsDisplayFixedPosition::TryMerge(nsDisplayItem* aItem) {
+  if (aItem->GetType() != TYPE_FIXED_POSITION)
+    return false;
+  // Items with the same fixed position frame can be merged.
+  nsDisplayFixedPosition* other = static_cast<nsDisplayFixedPosition*>(aItem);
+  if (other->mFrame != mFrame)
+    return false;
+  if (aItem->GetClip() != GetClip())
+    return false;
+  MergeFromTrackingMergedFrames(other);
+  return true;
+}
+
+nsDisplayStickyPosition::nsDisplayStickyPosition(nsDisplayListBuilder* aBuilder,
+                                                 nsIFrame* aFrame,
+                                                 nsDisplayList* aList)
+  : nsDisplayOwnLayer(aBuilder, aFrame, aList)
+{
+  MOZ_COUNT_CTOR(nsDisplayStickyPosition);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayStickyPosition::~nsDisplayStickyPosition() {
+  MOZ_COUNT_DTOR(nsDisplayStickyPosition);
+}
+#endif
+
+already_AddRefed<Layer>
+nsDisplayStickyPosition::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                    LayerManager* aManager,
+                                    const ContainerLayerParameters& aContainerParameters) {
+  RefPtr<Layer> layer =
+    nsDisplayOwnLayer::BuildLayer(aBuilder, aManager, aContainerParameters);
+
+  StickyScrollContainer* stickyScrollContainer = StickyScrollContainer::
+    GetStickyScrollContainerForFrame(mFrame);
+  if (!stickyScrollContainer) {
+    return layer.forget();
+  }
+
+  nsIFrame* scrollFrame = do_QueryFrame(stickyScrollContainer->ScrollFrame());
+  nsPresContext* presContext = scrollFrame->PresContext();
+
+  // Sticky position frames whose scroll frame is the root scroll frame are
+  // reflowed into the scroll-port size if one has been set.
+  nsSize scrollFrameSize = scrollFrame->GetSize();
+  if (scrollFrame == presContext->PresShell()->GetRootScrollFrame() &&
+      presContext->PresShell()->IsScrollPositionClampingScrollPortSizeSet()) {
+    scrollFrameSize = presContext->PresShell()->
+      GetScrollPositionClampingScrollPortSize();
+  }
+
+  nsLayoutUtils::SetFixedPositionLayerData(layer, scrollFrame,
+    nsRect(scrollFrame->GetOffsetToCrossDoc(ReferenceFrame()), scrollFrameSize),
+    mFrame, presContext, aContainerParameters);
+
+  ViewID scrollId = nsLayoutUtils::FindOrCreateIDFor(
+    stickyScrollContainer->ScrollFrame()->GetScrolledFrame()->GetContent());
+
+  float factor = presContext->AppUnitsPerDevPixel();
+  nsRect outer;
+  nsRect inner;
+  stickyScrollContainer->GetScrollRanges(mFrame, &outer, &inner);
+  LayerRect stickyOuter(NSAppUnitsToFloatPixels(outer.x, factor) *
+                          aContainerParameters.mXScale,
+                        NSAppUnitsToFloatPixels(outer.y, factor) *
+                          aContainerParameters.mYScale,
+                        NSAppUnitsToFloatPixels(outer.width, factor) *
+                          aContainerParameters.mXScale,
+                        NSAppUnitsToFloatPixels(outer.height, factor) *
+                          aContainerParameters.mYScale);
+  LayerRect stickyInner(NSAppUnitsToFloatPixels(inner.x, factor) *
+                          aContainerParameters.mXScale,
+                        NSAppUnitsToFloatPixels(inner.y, factor) *
+                          aContainerParameters.mYScale,
+                        NSAppUnitsToFloatPixels(inner.width, factor) *
+                          aContainerParameters.mXScale,
+                        NSAppUnitsToFloatPixels(inner.height, factor) *
+                          aContainerParameters.mYScale);
+  layer->SetStickyPositionData(scrollId, stickyOuter, stickyInner);
+
+  return layer.forget();
+}
+
+bool nsDisplayStickyPosition::TryMerge(nsDisplayItem* aItem) {
+  if (aItem->GetType() != TYPE_STICKY_POSITION)
+    return false;
+  // Items with the same fixed position frame can be merged.
+  nsDisplayStickyPosition* other = static_cast<nsDisplayStickyPosition*>(aItem);
+  if (other->mFrame != mFrame)
+    return false;
+  if (aItem->GetClip() != GetClip())
+    return false;
+  if (aItem->ScrollClip() != ScrollClip())
+    return false;
+  MergeFromTrackingMergedFrames(other);
+  return true;
+}
+
+nsDisplayScrollInfoLayer::nsDisplayScrollInfoLayer(
+  nsDisplayListBuilder* aBuilder,
+  nsIFrame* aScrolledFrame,
+  nsIFrame* aScrollFrame)
+  : nsDisplayWrapList(aBuilder, aScrollFrame)
+  , mScrollFrame(aScrollFrame)
+  , mScrolledFrame(aScrolledFrame)
+  , mScrollParentId(aBuilder->GetCurrentScrollParentId())
+{
+#ifdef NS_BUILD_REFCNT_LOGGING
+  MOZ_COUNT_CTOR(nsDisplayScrollInfoLayer);
+#endif
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayScrollInfoLayer::~nsDisplayScrollInfoLayer()
+{
+  MOZ_COUNT_DTOR(nsDisplayScrollInfoLayer);
+}
+#endif
+
+already_AddRefed<Layer>
+nsDisplayScrollInfoLayer::BuildLayer(nsDisplayListBuilder* aBuilder,
+                                     LayerManager* aManager,
+                                     const ContainerLayerParameters& aContainerParameters)
+{
+  // In general for APZ with event-regions we no longer have a need for
+  // scrollinfo layers. However, in some cases, there might be content that
+  // cannot be layerized, and so needs to scroll synchronously. To handle those
+  // cases, we still want to generate scrollinfo layers.
+
+  ContainerLayerParameters params = aContainerParameters;
+  if (mScrolledFrame->GetContent() &&
+      nsLayoutUtils::HasCriticalDisplayPort(mScrolledFrame->GetContent())) {
+    params.mInLowPrecisionDisplayPort = true;
+  }
+
+  return aManager->GetLayerBuilder()->
+    BuildContainerLayerFor(aBuilder, aManager, mFrame, this, &mList,
+                           params, nullptr,
+                           FrameLayerBuilder::CONTAINER_ALLOW_PULL_BACKGROUND_COLOR);
+}
+
+LayerState
+nsDisplayScrollInfoLayer::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                    LayerManager* aManager,
+                                    const ContainerLayerParameters& aParameters)
+{
+  return LAYER_ACTIVE_EMPTY;
+}
+
+UniquePtr<ScrollMetadata>
+nsDisplayScrollInfoLayer::ComputeScrollMetadata(Layer* aLayer,
+                                                const ContainerLayerParameters& aContainerParameters)
+{
+  ContainerLayerParameters params = aContainerParameters;
+  if (mScrolledFrame->GetContent() &&
+      nsLayoutUtils::HasCriticalDisplayPort(mScrolledFrame->GetContent())) {
+    params.mInLowPrecisionDisplayPort = true;
+  }
+
+  nsRect viewport = mScrollFrame->GetRect() -
+                    mScrollFrame->GetPosition() +
+                    mScrollFrame->GetOffsetToCrossDoc(ReferenceFrame());
+
+  ScrollMetadata metadata = nsLayoutUtils::ComputeScrollMetadata(
+      mScrolledFrame, mScrollFrame, mScrollFrame->GetContent(),
+      ReferenceFrame(), aLayer,
+      mScrollParentId, viewport, Nothing(), false, params);
+  metadata.GetMetrics().SetIsScrollInfoLayer(true);
+
+  return UniquePtr<ScrollMetadata>(new ScrollMetadata(metadata));
+}
+
+
+
+void
+nsDisplayScrollInfoLayer::WriteDebugInfo(std::stringstream& aStream)
+{
+  aStream << " (scrollframe " << mScrollFrame
+          << " scrolledFrame " << mScrolledFrame << ")";
+}
+
+nsDisplayZoom::nsDisplayZoom(nsDisplayListBuilder* aBuilder,
+                             nsIFrame* aFrame, nsDisplayList* aList,
+                             int32_t aAPD, int32_t aParentAPD,
+                             uint32_t aFlags)
+    : nsDisplaySubDocument(aBuilder, aFrame, aList, aFlags)
+    , mAPD(aAPD), mParentAPD(aParentAPD) {
+  MOZ_COUNT_CTOR(nsDisplayZoom);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayZoom::~nsDisplayZoom() {
+  MOZ_COUNT_DTOR(nsDisplayZoom);
+}
+#endif
+
+nsRect nsDisplayZoom::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  nsRect bounds = nsDisplaySubDocument::GetBounds(aBuilder, aSnap);
+  *aSnap = false;
+  return bounds.ScaleToOtherAppUnitsRoundOut(mAPD, mParentAPD);
+}
+
+void nsDisplayZoom::HitTest(nsDisplayListBuilder *aBuilder,
+                            const nsRect& aRect,
+                            HitTestState *aState,
+                            nsTArray<nsIFrame*> *aOutFrames)
+{
+  nsRect rect;
+  // A 1x1 rect indicates we are just hit testing a point, so pass down a 1x1
+  // rect as well instead of possibly rounding the width or height to zero.
+  if (aRect.width == 1 && aRect.height == 1) {
+    rect.MoveTo(aRect.TopLeft().ScaleToOtherAppUnits(mParentAPD, mAPD));
+    rect.width = rect.height = 1;
+  } else {
+    rect = aRect.ScaleToOtherAppUnitsRoundOut(mParentAPD, mAPD);
+  }
+  mList.HitTest(aBuilder, rect, aState, aOutFrames);
+}
+
+bool nsDisplayZoom::ComputeVisibility(nsDisplayListBuilder *aBuilder,
+                                      nsRegion *aVisibleRegion)
+{
+  // Convert the passed in visible region to our appunits.
+  nsRegion visibleRegion;
+  // mVisibleRect has been clipped to GetClippedBounds
+  visibleRegion.And(*aVisibleRegion, mVisibleRect);
+  visibleRegion = visibleRegion.ScaleToOtherAppUnitsRoundOut(mParentAPD, mAPD);
+  nsRegion originalVisibleRegion = visibleRegion;
+
+  nsRect transformedVisibleRect =
+    mVisibleRect.ScaleToOtherAppUnitsRoundOut(mParentAPD, mAPD);
+  bool retval;
+  // If we are to generate a scrollable layer we call
+  // nsDisplaySubDocument::ComputeVisibility to make the necessary adjustments
+  // for ComputeVisibility, it does all it's calculations in the child APD.
+  bool usingDisplayPort = UseDisplayPortForViewport(aBuilder, mFrame);
+  if (!(mFlags & GENERATE_SCROLLABLE_LAYER) || !usingDisplayPort) {
+    retval =
+      mList.ComputeVisibilityForSublist(aBuilder, &visibleRegion,
+                                        transformedVisibleRect);
+  } else {
+    retval =
+      nsDisplaySubDocument::ComputeVisibility(aBuilder, &visibleRegion);
+  }
+
+  nsRegion removed;
+  // removed = originalVisibleRegion - visibleRegion
+  removed.Sub(originalVisibleRegion, visibleRegion);
+  // Convert removed region to parent appunits.
+  removed = removed.ScaleToOtherAppUnitsRoundIn(mAPD, mParentAPD);
+  // aVisibleRegion = aVisibleRegion - removed (modulo any simplifications
+  // SubtractFromVisibleRegion does)
+  aBuilder->SubtractFromVisibleRegion(aVisibleRegion, removed);
+
+  return retval;
+}
+
+///////////////////////////////////////////////////
+// nsDisplayTransform Implementation
+//
+
+// Write #define UNIFIED_CONTINUATIONS here and in
+// TransformReferenceBox::Initialize to have the transform property try
+// to transform content with continuations as one unified block instead of
+// several smaller ones.  This is currently disabled because it doesn't work
+// correctly, since when the frames are initially being reflowed, their
+// continuations all compute their bounding rects independently of each other
+// and consequently get the wrong value.  Write #define DEBUG_HIT here to have
+// the nsDisplayTransform class dump out a bunch of information about hit
+// detection.
+#undef  UNIFIED_CONTINUATIONS
+#undef  DEBUG_HIT
+
+nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
+                                       nsIFrame *aFrame, nsDisplayList *aList,
+                                       const nsRect& aChildrenVisibleRect,
+                                       ComputeTransformFunction aTransformGetter,
+                                       uint32_t aIndex)
+  : nsDisplayItem(aBuilder, aFrame)
+  , mStoredList(aBuilder, aFrame, aList)
+  , mTransformGetter(aTransformGetter)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
+  , mChildrenVisibleRect(aChildrenVisibleRect)
+  , mIndex(aIndex)
+  , mNoExtendContext(false)
+  , mIsTransformSeparator(false)
+  , mTransformPreserves3DInited(false)
+  , mIsFullyVisible(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayTransform);
+  MOZ_ASSERT(aFrame, "Must have a frame!");
+  Init(aBuilder);
+}
+
+void
+nsDisplayTransform::SetReferenceFrameToAncestor(nsDisplayListBuilder* aBuilder)
+{
+  if (mFrame == aBuilder->RootReferenceFrame()) {
+    return;
+  }
+  nsIFrame *outerFrame = nsLayoutUtils::GetCrossDocParentFrame(mFrame);
+  mReferenceFrame =
+    aBuilder->FindReferenceFrameFor(outerFrame);
+  mToReferenceFrame = mFrame->GetOffsetToCrossDoc(mReferenceFrame);
+  if (nsLayoutUtils::IsFixedPosFrameInDisplayPort(mFrame)) {
+    // This is an odd special case. If we are both IsFixedPosFrameInDisplayPort
+    // and transformed that we are our own AGR parent.
+    // We want our frame to be our AGR because FrameLayerBuilder uses our AGR to
+    // determine if we are inside a fixed pos subtree. If we use the outer AGR
+    // from outside the fixed pos subtree FLB can't tell that we are fixed pos.
+    mAnimatedGeometryRoot = mAnimatedGeometryRootForChildren;
+  } else if (mFrame->StyleDisplay()->mPosition == NS_STYLE_POSITION_STICKY &&
+             IsStickyFrameActive(aBuilder, mFrame, nullptr)) {
+    // Similar to the IsFixedPosFrameInDisplayPort case we are our own AGR.
+    // We are inside the sticky position, so our AGR is the sticky positioned
+    // frame, which is our AGR, not the parent AGR.
+    mAnimatedGeometryRoot = mAnimatedGeometryRootForChildren;
+  } else if (mAnimatedGeometryRoot->mParentAGR) {
+    mAnimatedGeometryRootForScrollMetadata = mAnimatedGeometryRoot->mParentAGR;
+    if (!MayBeAnimated(aBuilder)) {
+      // If we're an animated transform then we want the same AGR as our children
+      // so that FrameLayerBuilder knows that this layer moves with the transform
+      // and won't compute occlusions. If we're not animated then use our parent
+      // AGR so that inactive transform layers can go in the same PaintedLayer as
+      // surrounding content.
+      mAnimatedGeometryRoot = mAnimatedGeometryRoot->mParentAGR;
+    }
+  }
+  mVisibleRect = aBuilder->GetDirtyRect() + mToReferenceFrame;
+}
+
+void
+nsDisplayTransform::Init(nsDisplayListBuilder* aBuilder)
+{
+  mHasBounds = false;
+  mStoredList.SetClip(aBuilder, DisplayItemClip::NoClip());
+  mStoredList.SetVisibleRect(mChildrenVisibleRect);
+}
+
+nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
+                                       nsIFrame *aFrame, nsDisplayList *aList,
+                                       const nsRect& aChildrenVisibleRect,
+                                       uint32_t aIndex,
+                                       bool aIsFullyVisible)
+  : nsDisplayItem(aBuilder, aFrame)
+  , mStoredList(aBuilder, aFrame, aList)
+  , mTransformGetter(nullptr)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
+  , mChildrenVisibleRect(aChildrenVisibleRect)
+  , mIndex(aIndex)
+  , mNoExtendContext(false)
+  , mIsTransformSeparator(false)
+  , mTransformPreserves3DInited(false)
+  , mIsFullyVisible(aIsFullyVisible)
+{
+  MOZ_COUNT_CTOR(nsDisplayTransform);
+  MOZ_ASSERT(aFrame, "Must have a frame!");
+  SetReferenceFrameToAncestor(aBuilder);
+  Init(aBuilder);
+  UpdateBoundsFor3D(aBuilder);
+}
+
+nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
+                                       nsIFrame *aFrame, nsDisplayItem *aItem,
+                                       const nsRect& aChildrenVisibleRect,
+                                       uint32_t aIndex)
+  : nsDisplayItem(aBuilder, aFrame)
+  , mStoredList(aBuilder, aFrame, aItem)
+  , mTransformGetter(nullptr)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
+  , mChildrenVisibleRect(aChildrenVisibleRect)
+  , mIndex(aIndex)
+  , mNoExtendContext(false)
+  , mIsTransformSeparator(false)
+  , mTransformPreserves3DInited(false)
+  , mIsFullyVisible(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayTransform);
+  MOZ_ASSERT(aFrame, "Must have a frame!");
+  SetReferenceFrameToAncestor(aBuilder);
+  Init(aBuilder);
+}
+
+nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
+                                       nsIFrame *aFrame, nsDisplayList *aList,
+                                       const nsRect& aChildrenVisibleRect,
+                                       const Matrix4x4& aTransform,
+                                       uint32_t aIndex)
+  : nsDisplayItem(aBuilder, aFrame)
+  , mStoredList(aBuilder, aFrame, aList)
+  , mTransform(aTransform)
+  , mTransformGetter(nullptr)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
+  , mChildrenVisibleRect(aChildrenVisibleRect)
+  , mIndex(aIndex)
+  , mNoExtendContext(false)
+  , mIsTransformSeparator(true)
+  , mTransformPreserves3DInited(false)
+  , mIsFullyVisible(false)
+{
+  MOZ_COUNT_CTOR(nsDisplayTransform);
+  MOZ_ASSERT(aFrame, "Must have a frame!");
+  Init(aBuilder);
+  UpdateBoundsFor3D(aBuilder);
+}
+
+/* Returns the delta specified by the transform-origin property.
+ * This is a positive delta, meaning that it indicates the direction to move
+ * to get from (0, 0) of the frame to the transform origin.  This function is
+ * called off the main thread.
+ */
+/* static */ Point3D
+nsDisplayTransform::GetDeltaToTransformOrigin(const nsIFrame* aFrame,
+                                              float aAppUnitsPerPixel,
+                                              const nsRect* aBoundsOverride)
+{
+  NS_PRECONDITION(aFrame, "Can't get delta for a null frame!");
+  NS_PRECONDITION(aFrame->IsTransformed() ||
+                  aFrame->BackfaceIsHidden() ||
+                  aFrame->Combines3DTransformWithAncestors(),
+                  "Shouldn't get a delta for an untransformed frame!");
+
+  if (!aFrame->IsTransformed()) {
+    return Point3D();
+  }
+
+  /* For both of the coordinates, if the value of transform is a
+   * percentage, it's relative to the size of the frame.  Otherwise, if it's
+   * a distance, it's already computed for us!
+   */
+  const nsStyleDisplay* display = aFrame->StyleDisplay();
+  // We don't use aBoundsOverride for SVG since we need to account for
+  // refBox.X/Y(). This happens to work because ReflowSVG sets the frame's
+  // mRect before calling FinishAndStoreOverflow so we don't need the override.
+  TransformReferenceBox refBox;
+  if (aBoundsOverride &&
+      !(aFrame->GetStateBits() & NS_FRAME_SVG_LAYOUT)) {
+    refBox.Init(aBoundsOverride->Size());
+  } else {
+    refBox.Init(aFrame);
+  }
+
+  /* Allows us to access dimension getters by index. */
+  float coords[2];
+  TransformReferenceBox::DimensionGetter dimensionGetter[] =
+    { &TransformReferenceBox::Width, &TransformReferenceBox::Height };
+  TransformReferenceBox::DimensionGetter offsetGetter[] =
+    { &TransformReferenceBox::X, &TransformReferenceBox::Y };
+
+  for (uint8_t index = 0; index < 2; ++index) {
+    /* If the transform-origin specifies a percentage, take the percentage
+     * of the size of the box.
+     */
+    const nsStyleCoord &coord = display->mTransformOrigin[index];
+    if (coord.GetUnit() == eStyleUnit_Calc) {
+      const nsStyleCoord::Calc *calc = coord.GetCalcValue();
+      coords[index] =
+        NSAppUnitsToFloatPixels((refBox.*dimensionGetter[index])(), aAppUnitsPerPixel) *
+          calc->mPercent +
+        NSAppUnitsToFloatPixels(calc->mLength, aAppUnitsPerPixel);
+    } else if (coord.GetUnit() == eStyleUnit_Percent) {
+      coords[index] =
+        NSAppUnitsToFloatPixels((refBox.*dimensionGetter[index])(), aAppUnitsPerPixel) *
+        coord.GetPercentValue();
+    } else {
+      MOZ_ASSERT(coord.GetUnit() == eStyleUnit_Coord, "unexpected unit");
+      coords[index] =
+        NSAppUnitsToFloatPixels(coord.GetCoordValue(), aAppUnitsPerPixel);
+    }
+
+    if (aFrame->GetStateBits() & NS_FRAME_SVG_LAYOUT) {
+      // SVG frames (unlike other frames) have a reference box that can be (and
+      // typically is) offset from the TopLeft() of the frame. We need to
+      // account for that here.
+      coords[index] +=
+        NSAppUnitsToFloatPixels((refBox.*offsetGetter[index])(), aAppUnitsPerPixel);
+    }
+  }
+
+  return Point3D(coords[0], coords[1],
+                 NSAppUnitsToFloatPixels(display->mTransformOrigin[2].GetCoordValue(),
+                                         aAppUnitsPerPixel));
+}
+
+/* static */ bool
+nsDisplayTransform::ComputePerspectiveMatrix(const nsIFrame* aFrame,
+                                             float aAppUnitsPerPixel,
+                                             Matrix4x4& aOutMatrix)
+{
+  NS_PRECONDITION(aFrame, "Can't get delta for a null frame!");
+  NS_PRECONDITION(aFrame->IsTransformed() ||
+                  aFrame->BackfaceIsHidden() ||
+                  aFrame->Combines3DTransformWithAncestors(),
+                  "Shouldn't get a delta for an untransformed frame!");
+  NS_PRECONDITION(aOutMatrix.IsIdentity(), "Must have a blank output matrix");
+
+  if (!aFrame->IsTransformed()) {
+    return false;
+  }
+
+  /* Find our containing block, which is the element that provides the
+   * value for perspective we need to use
+   */
+
+  //TODO: Is it possible that the cbFrame's bounds haven't been set correctly yet
+  // (similar to the aBoundsOverride case for GetResultingTransformMatrix)?
+  nsIFrame* cbFrame = aFrame->GetContainingBlock(nsIFrame::SKIP_SCROLLED_FRAME);
+  if (!cbFrame) {
+    return false;
+  }
+
+  /* Grab the values for perspective and perspective-origin (if present) */
+
+  const nsStyleDisplay* cbDisplay = cbFrame->StyleDisplay();
+  if (cbDisplay->mChildPerspective.GetUnit() != eStyleUnit_Coord) {
+    return false;
+  }
+  nscoord perspective = cbDisplay->mChildPerspective.GetCoordValue();
+  if (perspective < 0) {
+    return true;
+  }
+
+  TransformReferenceBox refBox(cbFrame);
+
+  /* Allows us to access named variables by index. */
+  Point3D perspectiveOrigin;
+  gfx::Float* coords[2] = {&perspectiveOrigin.x, &perspectiveOrigin.y};
+  TransformReferenceBox::DimensionGetter dimensionGetter[] =
+    { &TransformReferenceBox::Width, &TransformReferenceBox::Height };
+
+  /* For both of the coordinates, if the value of perspective-origin is a
+   * percentage, it's relative to the size of the frame.  Otherwise, if it's
+   * a distance, it's already computed for us!
+   */
+  for (uint8_t index = 0; index < 2; ++index) {
+    /* If the -transform-origin specifies a percentage, take the percentage
+     * of the size of the box.
+     */
+    const nsStyleCoord &coord = cbDisplay->mPerspectiveOrigin[index];
+    if (coord.GetUnit() == eStyleUnit_Calc) {
+      const nsStyleCoord::Calc *calc = coord.GetCalcValue();
+      *coords[index] =
+        NSAppUnitsToFloatPixels((refBox.*dimensionGetter[index])(), aAppUnitsPerPixel) *
+          calc->mPercent +
+        NSAppUnitsToFloatPixels(calc->mLength, aAppUnitsPerPixel);
+    } else if (coord.GetUnit() == eStyleUnit_Percent) {
+      *coords[index] =
+        NSAppUnitsToFloatPixels((refBox.*dimensionGetter[index])(), aAppUnitsPerPixel) *
+        coord.GetPercentValue();
+    } else {
+      MOZ_ASSERT(coord.GetUnit() == eStyleUnit_Coord, "unexpected unit");
+      *coords[index] =
+        NSAppUnitsToFloatPixels(coord.GetCoordValue(), aAppUnitsPerPixel);
+    }
+  }
+
+  /* GetOffsetTo computes the offset required to move from 0,0 in cbFrame to 0,0
+   * in aFrame. Although we actually want the inverse of this, it's faster to
+   * compute this way.
+   */
+  nsPoint frameToCbOffset = -aFrame->GetOffsetTo(cbFrame);
+  Point3D frameToCbGfxOffset(
+            NSAppUnitsToFloatPixels(frameToCbOffset.x, aAppUnitsPerPixel),
+            NSAppUnitsToFloatPixels(frameToCbOffset.y, aAppUnitsPerPixel),
+            0.0f);
+
+  /* Move the perspective origin to be relative to aFrame, instead of relative
+   * to the containing block which is how it was specified in the style system.
+   */
+  perspectiveOrigin += frameToCbGfxOffset;
+
+  Float perspectivePx = std::max(NSAppUnitsToFloatPixels(perspective,
+                                                         aAppUnitsPerPixel),
+                                 std::numeric_limits<Float>::epsilon());
+  aOutMatrix._34 = -1.0 / perspectivePx;
+  aOutMatrix.ChangeBasis(perspectiveOrigin);
+  return true;
+}
+
+nsDisplayTransform::FrameTransformProperties::FrameTransformProperties(const nsIFrame* aFrame,
+                                                                       float aAppUnitsPerPixel,
+                                                                       const nsRect* aBoundsOverride)
+  : mFrame(aFrame)
+  , mTransformList(aFrame->StyleDisplay()->mSpecifiedTransform)
+  , mToTransformOrigin(GetDeltaToTransformOrigin(aFrame, aAppUnitsPerPixel, aBoundsOverride))
+{
+}
+
+/* Wraps up the transform matrix in a change-of-basis matrix pair that
+ * translates from local coordinate space to transform coordinate space, then
+ * hands it back.
+ */
+Matrix4x4
+nsDisplayTransform::GetResultingTransformMatrix(const FrameTransformProperties& aProperties,
+                                                const nsPoint& aOrigin,
+                                                float aAppUnitsPerPixel,
+                                                uint32_t aFlags,
+                                                const nsRect* aBoundsOverride)
+{
+  return GetResultingTransformMatrixInternal(aProperties, aOrigin, aAppUnitsPerPixel,
+                                             aFlags, aBoundsOverride);
+}
+
+Matrix4x4
+nsDisplayTransform::GetResultingTransformMatrix(const nsIFrame* aFrame,
+                                                const nsPoint& aOrigin,
+                                                float aAppUnitsPerPixel,
+                                                uint32_t aFlags,
+                                                const nsRect* aBoundsOverride)
+{
+  FrameTransformProperties props(aFrame,
+                                 aAppUnitsPerPixel,
+                                 aBoundsOverride);
+
+  return GetResultingTransformMatrixInternal(props, aOrigin, aAppUnitsPerPixel,
+                                             aFlags, aBoundsOverride);
+}
+
+Matrix4x4
+nsDisplayTransform::GetResultingTransformMatrixInternal(const FrameTransformProperties& aProperties,
+                                                        const nsPoint& aOrigin,
+                                                        float aAppUnitsPerPixel,
+                                                        uint32_t aFlags,
+                                                        const nsRect* aBoundsOverride)
+{
+  const nsIFrame *frame = aProperties.mFrame;
+  NS_ASSERTION(frame || !(aFlags & INCLUDE_PERSPECTIVE), "Must have a frame to compute perspective!");
+
+  // Get the underlying transform matrix:
+
+  // We don't use aBoundsOverride for SVG since we need to account for
+  // refBox.X/Y(). This happens to work because ReflowSVG sets the frame's
+  // mRect before calling FinishAndStoreOverflow so we don't need the override.
+  TransformReferenceBox refBox;
+  if (aBoundsOverride &&
+      (!frame || !(frame->GetStateBits() & NS_FRAME_SVG_LAYOUT))) {
+    refBox.Init(aBoundsOverride->Size());
+  } else {
+    refBox.Init(frame);
+  }
+
+  /* Get the matrix, then change its basis to factor in the origin. */
+  RuleNodeCacheConditions dummy;
+  bool dummyBool;
+  Matrix4x4 result;
+  // Call IsSVGTransformed() regardless of the value of
+  // disp->mSpecifiedTransform, since we still need any transformFromSVGParent.
+  Matrix svgTransform, transformFromSVGParent;
+  bool hasSVGTransforms =
+    frame && frame->IsSVGTransformed(&svgTransform, &transformFromSVGParent);
+  bool hasTransformFromSVGParent =
+    hasSVGTransforms && !transformFromSVGParent.IsIdentity();
+  /* Transformed frames always have a transform, or are preserving 3d (and might still have perspective!) */
+  if (aProperties.mTransformList) {
+    result = nsStyleTransformMatrix::ReadTransforms(aProperties.mTransformList->mHead,
+                                                    frame ? frame->StyleContext() : nullptr,
+                                                    frame ? frame->PresContext() : nullptr,
+                                                    dummy, refBox, aAppUnitsPerPixel,
+                                                    &dummyBool);
+  } else if (hasSVGTransforms) {
+    // Correct the translation components for zoom:
+    float pixelsPerCSSPx = frame->PresContext()->AppUnitsPerCSSPixel() /
+                             aAppUnitsPerPixel;
+    svgTransform._31 *= pixelsPerCSSPx;
+    svgTransform._32 *= pixelsPerCSSPx;
+    result = Matrix4x4::From2D(svgTransform);
+  }
+
+
+  Matrix4x4 perspectiveMatrix;
+  bool hasPerspective = aFlags & INCLUDE_PERSPECTIVE;
+  if (hasPerspective) {
+    hasPerspective = ComputePerspectiveMatrix(frame, aAppUnitsPerPixel,
+                                              perspectiveMatrix);
+  }
+
+  if (!hasSVGTransforms || !hasTransformFromSVGParent) {
+    // This is a simplification of the following |else| block, the
+    // simplification being possible because we don't need to apply
+    // mToTransformOrigin between two transforms.
+    result.ChangeBasis(aProperties.mToTransformOrigin);
+  } else {
+    Point3D refBoxOffset(NSAppUnitsToFloatPixels(refBox.X(), aAppUnitsPerPixel),
+                         NSAppUnitsToFloatPixels(refBox.Y(), aAppUnitsPerPixel),
+                         0);
+    // We have both a transform and children-only transform. The
+    // 'transform-origin' must apply between the two, so we need to apply it
+    // now before we apply transformFromSVGParent. Since mToTransformOrigin is
+    // relative to the frame's TopLeft(), we need to convert it to SVG user
+    // space by subtracting refBoxOffset. (Then after applying
+    // transformFromSVGParent we have to reapply refBoxOffset below.)
+    result.ChangeBasis(aProperties.mToTransformOrigin - refBoxOffset);
+
+    // Now apply the children-only transforms, converting the translation
+    // components to device pixels:
+    float pixelsPerCSSPx =
+      frame->PresContext()->AppUnitsPerCSSPixel() / aAppUnitsPerPixel;
+    transformFromSVGParent._31 *= pixelsPerCSSPx;
+    transformFromSVGParent._32 *= pixelsPerCSSPx;
+    result = result * Matrix4x4::From2D(transformFromSVGParent);
+
+    // Similar to the code in the |if| block above, but since we've accounted
+    // for mToTransformOrigin so we don't include that. We also need to reapply
+    // refBoxOffset.
+    result.ChangeBasis(refBoxOffset);
+  }
+
+  if (hasPerspective) {
+    result = result * perspectiveMatrix;
+  }
+
+  if ((aFlags & INCLUDE_PRESERVE3D_ANCESTORS) &&
+      frame && frame->Combines3DTransformWithAncestors()) {
+    // Include the transform set on our parent
+    NS_ASSERTION(frame->GetParent() &&
+                 frame->GetParent()->IsTransformed() &&
+                 frame->GetParent()->Extend3DContext(),
+                 "Preserve3D mismatch!");
+    FrameTransformProperties props(frame->GetParent(),
+                                   aAppUnitsPerPixel,
+                                   nullptr);
+
+    uint32_t flags = aFlags & (INCLUDE_PRESERVE3D_ANCESTORS|INCLUDE_PERSPECTIVE);
+
+    // If this frame isn't transformed (but we exist for backface-visibility),
+    // then we're not a reference frame so no offset to origin will be added.
+    // Otherwise we need to manually translate into our parent's coordinate
+    // space.
+    if (frame->IsTransformed()) {
+      nsLayoutUtils::PostTranslate(result, frame->GetPosition(), aAppUnitsPerPixel, !hasSVGTransforms);
+    }
+    Matrix4x4 parent =
+      GetResultingTransformMatrixInternal(props,
+                                          nsPoint(0, 0),
+                                          aAppUnitsPerPixel, flags,
+                                          nullptr);
+    result = result * parent;
+  }
+
+  if (aFlags & OFFSET_BY_ORIGIN) {
+    nsLayoutUtils::PostTranslate(result, aOrigin, aAppUnitsPerPixel, !hasSVGTransforms);
+  }
+
+  return result;
+}
+
+bool
+nsDisplayOpacity::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder)
+{
+  if (ActiveLayerTracker::IsStyleAnimated(aBuilder, mFrame, eCSSProperty_opacity)) {
+    return true;
+  }
+
+  EffectCompositor::SetPerformanceWarning(
+    mFrame, eCSSProperty_opacity,
+    AnimationPerformanceWarning(
+      AnimationPerformanceWarning::Type::OpacityFrameInactive));
+
+  return false;
+}
+
+bool
+nsDisplayTransform::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder)
+{
+  return mIsFullyVisible;
+}
+
+/* static */ bool
+nsDisplayTransform::ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBuilder,
+                                                      nsIFrame* aFrame)
+{
+  // Elements whose transform has been modified recently, or which
+  // have a compositor-animated transform, can be prerendered. An element
+  // might have only just had its transform animated in which case
+  // the ActiveLayerManager may not have been notified yet.
+  if (!ActiveLayerTracker::IsStyleMaybeAnimated(aFrame, eCSSProperty_transform) &&
+      !EffectCompositor::HasAnimationsForCompositor(aFrame,
+                                                    eCSSProperty_transform)) {
+    EffectCompositor::SetPerformanceWarning(
+      aFrame, eCSSProperty_transform,
+      AnimationPerformanceWarning(
+        AnimationPerformanceWarning::Type::TransformFrameInactive));
+
+    return false;
+  }
+
+  nsSize refSize = aBuilder->RootReferenceFrame()->GetSize();
+  // Only prerender if the transformed frame's size is <= the
+  // reference frame size (~viewport), allowing a 1/8th fuzz factor
+  // for shadows, borders, etc.
+  refSize += nsSize(refSize.width / 8, refSize.height / 8);
+  gfxSize scale = nsLayoutUtils::GetTransformToAncestorScale(aFrame);
+  nsSize frameSize = nsSize(
+    aFrame->GetVisualOverflowRectRelativeToSelf().Size().width * scale.width,
+    aFrame->GetVisualOverflowRectRelativeToSelf().Size().height * scale.height);
+  nscoord maxInAppUnits = nscoord_MAX;
+  if (frameSize <= refSize) {
+    maxInAppUnits = aFrame->PresContext()->DevPixelsToAppUnits(4096);
+    if (frameSize <= nsSize(maxInAppUnits, maxInAppUnits)) {
+      return true;
+    }
+  }
+
+  nsRect visual = aFrame->GetVisualOverflowRect();
+
+
+  EffectCompositor::SetPerformanceWarning(
+    aFrame, eCSSProperty_transform,
+    AnimationPerformanceWarning(
+      AnimationPerformanceWarning::Type::ContentTooLarge,
+      {
+        nsPresContext::AppUnitsToIntCSSPixels(frameSize.width),
+        nsPresContext::AppUnitsToIntCSSPixels(frameSize.height),
+        nsPresContext::AppUnitsToIntCSSPixels(refSize.width),
+        nsPresContext::AppUnitsToIntCSSPixels(refSize.height),
+        nsPresContext::AppUnitsToIntCSSPixels(visual.width),
+        nsPresContext::AppUnitsToIntCSSPixels(visual.height),
+        nsPresContext::AppUnitsToIntCSSPixels(maxInAppUnits)
+      }));
+  return false;
+}
+
+/* If the matrix is singular, or a hidden backface is shown, the frame won't be visible or hit. */
+static bool IsFrameVisible(nsIFrame* aFrame, const Matrix4x4& aMatrix)
+{
+  if (aMatrix.IsSingular()) {
+    return false;
+  }
+  if (aFrame->BackfaceIsHidden() && aMatrix.IsBackfaceVisible()) {
+    return false;
+  }
+  return true;
+}
+
+const Matrix4x4&
+nsDisplayTransform::GetTransform()
+{
+  if (mTransform.IsIdentity()) {
+    float scale = mFrame->PresContext()->AppUnitsPerDevPixel();
+    Point3D newOrigin =
+      Point3D(NSAppUnitsToFloatPixels(mToReferenceFrame.x, scale),
+              NSAppUnitsToFloatPixels(mToReferenceFrame.y, scale),
+              0.0f);
+    if (mTransformGetter) {
+      mTransform = mTransformGetter(mFrame, scale);
+      mTransform.ChangeBasis(newOrigin.x, newOrigin.y, newOrigin.z);
+    } else if (!mIsTransformSeparator) {
+      DebugOnly<bool> isReference =
+        mFrame->IsTransformed() ||
+        mFrame->Combines3DTransformWithAncestors() || mFrame->Extend3DContext();
+      MOZ_ASSERT(isReference);
+      mTransform =
+        GetResultingTransformMatrix(mFrame, ToReferenceFrame(),
+                                    scale, INCLUDE_PERSPECTIVE|OFFSET_BY_ORIGIN);
+    }
+  }
+  return mTransform;
+}
+
+Matrix4x4
+nsDisplayTransform::GetTransformForRendering()
+{
+  if (!mFrame->HasPerspective() || mTransformGetter || mIsTransformSeparator) {
+    return GetTransform();
+  }
+  MOZ_ASSERT(!mTransformGetter);
+
+  float scale = mFrame->PresContext()->AppUnitsPerDevPixel();
+  // Don't include perspective transform, or the offset to origin, since
+  // nsDisplayPerspective will handle both of those.
+  return GetResultingTransformMatrix(mFrame, ToReferenceFrame(), scale, 0);
+}
+
+const Matrix4x4&
+nsDisplayTransform::GetAccumulatedPreserved3DTransform(nsDisplayListBuilder* aBuilder)
+{
+  MOZ_ASSERT(!mFrame->Extend3DContext() || IsLeafOf3DContext());
+  // XXX: should go back to fix mTransformGetter.
+  if (!mTransformPreserves3DInited) {
+    mTransformPreserves3DInited = true;
+    if (!IsLeafOf3DContext()) {
+      mTransformPreserves3D = GetTransform();
+      return mTransformPreserves3D;
+    }
+
+    const nsIFrame* establisher; // Establisher of the 3D rendering context.
+    for (establisher = mFrame;
+         establisher && establisher->Combines3DTransformWithAncestors();
+         establisher = nsLayoutUtils::GetCrossDocParentFrame(establisher)) {
+    }
+    const nsIFrame* establisherReference =
+      aBuilder->FindReferenceFrameFor(nsLayoutUtils::GetCrossDocParentFrame(establisher));
+
+    nsPoint offset = establisher->GetOffsetToCrossDoc(establisherReference);
+    float scale = mFrame->PresContext()->AppUnitsPerDevPixel();
+    uint32_t flags = INCLUDE_PRESERVE3D_ANCESTORS|INCLUDE_PERSPECTIVE|OFFSET_BY_ORIGIN;
+    mTransformPreserves3D =
+      GetResultingTransformMatrix(mFrame, offset, scale, flags);
+  }
+  return mTransformPreserves3D;
+}
+
+bool
+nsDisplayTransform::ShouldBuildLayerEvenIfInvisible(nsDisplayListBuilder* aBuilder)
+{
+  // The visible rect of a Preserves-3D frame is just an intermediate
+  // result.  It should always build a layer to make sure it is
+  // rendering correctly.
+  return MayBeAnimated(aBuilder) || mFrame->Combines3DTransformWithAncestors();
+}
+
+already_AddRefed<Layer> nsDisplayTransform::BuildLayer(nsDisplayListBuilder *aBuilder,
+                                                       LayerManager *aManager,
+                                                       const ContainerLayerParameters& aContainerParameters)
+{
+  // While generating a glyph mask, the transform vector of the root frame had
+  // been applied into the target context, so stop applying it again here.
+  const bool shouldSkipTransform =
+    (aBuilder->RootReferenceFrame() == mFrame) &&
+    (aBuilder->IsForGenerateGlyphMask() || aBuilder->IsForPaintingSelectionBG());
+
+  /* For frames without transform, it would not be removed for
+   * backface hidden here.  But, it would be removed by the init
+   * function of nsDisplayTransform.
+   */
+  const Matrix4x4& newTransformMatrix =
+    shouldSkipTransform ? Matrix4x4(): GetTransformForRendering();
+
+  uint32_t flags = FrameLayerBuilder::CONTAINER_ALLOW_PULL_BACKGROUND_COLOR;
+  RefPtr<ContainerLayer> container = aManager->GetLayerBuilder()->
+    BuildContainerLayerFor(aBuilder, aManager, mFrame, this, mStoredList.GetChildren(),
+                           aContainerParameters, &newTransformMatrix, flags);
+
+  if (!container) {
+    return nullptr;
+  }
+
+  // Add the preserve-3d flag for this layer, BuildContainerLayerFor clears all flags,
+  // so we never need to explicitely unset this flag.
+  if (mFrame->Extend3DContext() && !mNoExtendContext) {
+    container->SetContentFlags(container->GetContentFlags() | Layer::CONTENT_EXTEND_3D_CONTEXT);
+  } else {
+    container->SetContentFlags(container->GetContentFlags() & ~Layer::CONTENT_EXTEND_3D_CONTEXT);
+  }
+
+  nsDisplayListBuilder::AddAnimationsAndTransitionsToLayer(container, aBuilder,
+                                                           this, mFrame,
+                                                           eCSSProperty_transform);
+  if (mIsFullyVisible && MayBeAnimated(aBuilder)) {
+    // Only allow async updates to the transform if we're an animated layer, since that's what
+    // triggers us to set the correct AGR in the constructor and makes sure FrameLayerBuilder
+    // won't compute occlusions for this layer.
+    container->SetUserData(nsIFrame::LayerIsPrerenderedDataKey(),
+                           /*the value is irrelevant*/nullptr);
+    container->SetContentFlags(container->GetContentFlags() | Layer::CONTENT_MAY_CHANGE_TRANSFORM);
+  } else {
+    container->RemoveUserData(nsIFrame::LayerIsPrerenderedDataKey());
+    container->SetContentFlags(container->GetContentFlags() & ~Layer::CONTENT_MAY_CHANGE_TRANSFORM);
+  }
+  return container.forget();
+}
+
+bool
+nsDisplayTransform::MayBeAnimated(nsDisplayListBuilder* aBuilder)
+{
+  // Here we check if the *post-transform* bounds of this item are big enough
+  // to justify an active layer.
+  if (ActiveLayerTracker::IsStyleAnimated(aBuilder,
+                                          mFrame,
+                                          eCSSProperty_transform) ||
+      EffectCompositor::HasAnimationsForCompositor(mFrame,
+                                                   eCSSProperty_transform)) {
+    if (!IsItemTooSmallForActiveLayer(mFrame)) {
+      return true;
+    }
+    SetAnimationPerformanceWarningForTooSmallItem(mFrame, eCSSProperty_transform);
+  }
+  return false;
+}
+
+nsDisplayItem::LayerState
+nsDisplayTransform::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                  LayerManager* aManager,
+                                  const ContainerLayerParameters& aParameters) {
+  // If the transform is 3d, the layer takes part in preserve-3d
+  // sorting, or the layer is a separator then we *always* want this
+  // to be an active layer.
+  if (!GetTransform().Is2D() || mFrame->Combines3DTransformWithAncestors() ||
+      mIsTransformSeparator) {
+    return LAYER_ACTIVE_FORCE;
+  }
+
+  if (MayBeAnimated(aBuilder)) {
+    // Returns LAYER_ACTIVE_FORCE to avoid flatterning the layer for async
+    // animations.
+    return LAYER_ACTIVE_FORCE;
+  }
+
+  // Expect the child display items to have this frame as their animated
+  // geometry root (since it will be their reference frame). If they have a
+  // different animated geometry root, we'll make this an active layer so the
+  // animation can be accelerated.
+  return RequiredLayerStateForChildren(aBuilder, aManager, aParameters,
+    *mStoredList.GetChildren(), mAnimatedGeometryRootForChildren);
+}
+
+bool nsDisplayTransform::ComputeVisibility(nsDisplayListBuilder *aBuilder,
+                                             nsRegion *aVisibleRegion)
+{
+  /* As we do this, we need to be sure to
+   * untransform the visible rect, since we want everything that's painting to
+   * think that it's painting in its original rectangular coordinate space.
+   * If we can't untransform, take the entire overflow rect */
+  nsRect untransformedVisibleRect;
+  if (!UntransformVisibleRect(aBuilder, &untransformedVisibleRect))
+  {
+    untransformedVisibleRect = mFrame->GetVisualOverflowRectRelativeToSelf();
+  }
+  nsRegion untransformedVisible = untransformedVisibleRect;
+  // Call RecomputeVisiblity instead of ComputeVisibility since
+  // nsDisplayItem::ComputeVisibility should only be called from
+  // nsDisplayList::ComputeVisibility (which sets mVisibleRect on the item)
+  mStoredList.RecomputeVisibility(aBuilder, &untransformedVisible);
+  return true;
+}
+
+#ifdef DEBUG_HIT
+#include <time.h>
+#endif
+
+/* HitTest does some fun stuff with matrix transforms to obtain the answer. */
+void nsDisplayTransform::HitTest(nsDisplayListBuilder *aBuilder,
+                                 const nsRect& aRect,
+                                 HitTestState *aState,
+                                 nsTArray<nsIFrame*> *aOutFrames)
+{
+  if (aState->mInPreserves3D) {
+    mStoredList.HitTest(aBuilder, aRect, aState, aOutFrames);
+    return;
+  }
+
+  /* Here's how this works:
+   * 1. Get the matrix.  If it's singular, abort (clearly we didn't hit
+   *    anything).
+   * 2. Invert the matrix.
+   * 3. Use it to transform the rect into the correct space.
+   * 4. Pass that rect down through to the list's version of HitTest.
+   */
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  Matrix4x4 matrix = GetAccumulatedPreserved3DTransform(aBuilder);
+
+  if (!IsFrameVisible(mFrame, matrix)) {
+    return;
+  }
+
+  /* We want to go from transformed-space to regular space.
+   * Thus we have to invert the matrix, which normally does
+   * the reverse operation (e.g. regular->transformed)
+   */
+
+  /* Now, apply the transform and pass it down the channel. */
+  matrix.Invert();
+  nsRect resultingRect;
+  if (aRect.width == 1 && aRect.height == 1) {
+    // Magic width/height indicating we're hit testing a point, not a rect
+    Point4D point = matrix.ProjectPoint(Point(NSAppUnitsToFloatPixels(aRect.x, factor),
+                                              NSAppUnitsToFloatPixels(aRect.y, factor)));
+    if (!point.HasPositiveWCoord()) {
+      return;
+    }
+
+    Point point2d = point.As2DPoint();
+
+    resultingRect = nsRect(NSFloatPixelsToAppUnits(float(point2d.x), factor),
+                           NSFloatPixelsToAppUnits(float(point2d.y), factor),
+                           1, 1);
+
+  } else {
+    Rect originalRect(NSAppUnitsToFloatPixels(aRect.x, factor),
+                      NSAppUnitsToFloatPixels(aRect.y, factor),
+                      NSAppUnitsToFloatPixels(aRect.width, factor),
+                      NSAppUnitsToFloatPixels(aRect.height, factor));
+
+
+    bool snap;
+    nsRect childBounds = mStoredList.GetBounds(aBuilder, &snap);
+    Rect childGfxBounds(NSAppUnitsToFloatPixels(childBounds.x, factor),
+                        NSAppUnitsToFloatPixels(childBounds.y, factor),
+                        NSAppUnitsToFloatPixels(childBounds.width, factor),
+                        NSAppUnitsToFloatPixels(childBounds.height, factor));
+
+    Rect rect = matrix.ProjectRectBounds(originalRect, childGfxBounds);
+
+    resultingRect = nsRect(NSFloatPixelsToAppUnits(float(rect.X()), factor),
+                           NSFloatPixelsToAppUnits(float(rect.Y()), factor),
+                           NSFloatPixelsToAppUnits(float(rect.Width()), factor),
+                           NSFloatPixelsToAppUnits(float(rect.Height()), factor));
+  }
+
+  if (resultingRect.IsEmpty()) {
+    return;
+  }
+
+
+#ifdef DEBUG_HIT
+  printf("Frame: %p\n", dynamic_cast<void *>(mFrame));
+  printf("  Untransformed point: (%f, %f)\n", resultingRect.X(), resultingRect.Y());
+  uint32_t originalFrameCount = aOutFrames.Length();
+#endif
+
+  mStoredList.HitTest(aBuilder, resultingRect, aState, aOutFrames);
+
+#ifdef DEBUG_HIT
+  if (originalFrameCount != aOutFrames.Length())
+    printf("  Hit! Time: %f, first frame: %p\n", static_cast<double>(clock()),
+           dynamic_cast<void *>(aOutFrames.ElementAt(0)));
+  printf("=== end of hit test ===\n");
+#endif
+
+}
+
+float
+nsDisplayTransform::GetHitDepthAtPoint(nsDisplayListBuilder* aBuilder, const nsPoint& aPoint)
+{
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  Matrix4x4 matrix = GetAccumulatedPreserved3DTransform(aBuilder);
+
+  NS_ASSERTION(IsFrameVisible(mFrame, matrix),
+               "We can't have hit a frame that isn't visible!");
+
+  Matrix4x4 inverse = matrix;
+  inverse.Invert();
+  Point4D point = inverse.ProjectPoint(Point(NSAppUnitsToFloatPixels(aPoint.x, factor),
+                                             NSAppUnitsToFloatPixels(aPoint.y, factor)));
+
+  Point point2d = point.As2DPoint();
+
+  Point3D transformed = matrix.TransformPoint(Point3D(point2d.x, point2d.y, 0));
+  return transformed.z;
+}
+
+/* The bounding rectangle for the object is the overflow rectangle translated
+ * by the reference point.
+ */
+nsRect
+nsDisplayTransform::GetBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
+{
+  *aSnap = false;
+
+  if (mHasBounds) {
+    return mBounds;
+  }
+
+  if (mFrame->Extend3DContext() && !mIsTransformSeparator) {
+    return nsRect();
+  }
+
+  nsRect untransformedBounds = mStoredList.GetBounds(aBuilder, aSnap);
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  mBounds = nsLayoutUtils::MatrixTransformRect(untransformedBounds,
+                                               GetTransform(),
+                                               factor);
+  mHasBounds = true;
+  return mBounds;
+}
+
+void
+nsDisplayTransform::ComputeBounds(nsDisplayListBuilder* aBuilder)
+{
+  MOZ_ASSERT(mFrame->Extend3DContext() || IsLeafOf3DContext());
+
+  /* For some cases, the transform would make an empty bounds, but it
+   * may be turned back again to get a non-empty bounds.  We should
+   * not depend on transforming bounds level by level.
+   *
+   * Here, it applies accumulated transforms on the leaf frames of the
+   * 3d rendering context, and track and accmulate bounds at
+   * nsDisplayListBuilder.
+   */
+  nsDisplayListBuilder::AutoAccumulateTransform accTransform(aBuilder);
+
+  accTransform.Accumulate(GetTransform());
+
+  if (!IsLeafOf3DContext()) {
+    // Do not dive into another 3D context.
+    mStoredList.DoUpdateBoundsPreserves3D(aBuilder);
+  }
+
+  /* For Preserves3D, it is bounds of only children as leaf frames.
+   * For non-leaf frames, their bounds are accumulated and kept at
+   * nsDisplayListBuilder.
+   */
+  bool snap;
+  nsRect untransformedBounds = mStoredList.GetBounds(aBuilder, &snap);
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  nsRect rect =
+    nsLayoutUtils::MatrixTransformRect(untransformedBounds,
+                                       accTransform.GetCurrentTransform(),
+                                       factor);
+
+  aBuilder->AccumulateRect(rect);
+}
+
+/* The transform is opaque iff the transform consists solely of scales and
+ * translations and if the underlying content is opaque.  Thus if the transform
+ * is of the form
+ *
+ * |a c e|
+ * |b d f|
+ * |0 0 1|
+ *
+ * We need b and c to be zero.
+ *
+ * We also need to check whether the underlying opaque content completely fills
+ * our visible rect. We use UntransformRect which expands to the axis-aligned
+ * bounding rect, but that's OK since if
+ * mStoredList.GetVisibleRect().Contains(untransformedVisible), then it
+ * certainly contains the actual (non-axis-aligned) untransformed rect.
+ */
+nsRegion nsDisplayTransform::GetOpaqueRegion(nsDisplayListBuilder *aBuilder,
+                                             bool* aSnap)
+{
+  *aSnap = false;
+  nsRect untransformedVisible;
+  if (!UntransformVisibleRect(aBuilder, &untransformedVisible)) {
+      return nsRegion();
+  }
+
+  const Matrix4x4& matrix = GetTransform();
+
+  nsRegion result;
+  Matrix matrix2d;
+  bool tmpSnap;
+  if (matrix.Is2D(&matrix2d) &&
+      matrix2d.PreservesAxisAlignedRectangles() &&
+      mStoredList.GetOpaqueRegion(aBuilder, &tmpSnap).Contains(untransformedVisible)) {
+    result = mVisibleRect.Intersect(GetBounds(aBuilder, &tmpSnap));
+  }
+  return result;
+}
+
+/* The transform is uniform if it fills the entire bounding rect and the
+ * wrapped list is uniform.  See GetOpaqueRegion for discussion of why this
+ * works.
+ */
+Maybe<nscolor>
+nsDisplayTransform::IsUniform(nsDisplayListBuilder *aBuilder)
+{
+  nsRect untransformedVisible;
+  if (!UntransformVisibleRect(aBuilder, &untransformedVisible)) {
+    return Nothing();
+  }
+  const Matrix4x4& matrix = GetTransform();
+
+  Matrix matrix2d;
+  if (matrix.Is2D(&matrix2d) &&
+      matrix2d.PreservesAxisAlignedRectangles() &&
+      mStoredList.GetVisibleRect().Contains(untransformedVisible)) {
+    return mStoredList.IsUniform(aBuilder);
+  }
+
+  return Nothing();
+}
+
+/* If UNIFIED_CONTINUATIONS is defined, we can merge two display lists that
+ * share the same underlying content.  Otherwise, doing so results in graphical
+ * glitches.
+ */
+#ifndef UNIFIED_CONTINUATIONS
+
+bool
+nsDisplayTransform::TryMerge(nsDisplayItem *aItem)
+{
+  return false;
+}
+
+#else
+
+bool
+nsDisplayTransform::TryMerge(nsDisplayItem *aItem)
+{
+  NS_PRECONDITION(aItem, "Why did you try merging with a null item?");
+
+  /* Make sure that we're dealing with two transforms. */
+  if (aItem->GetType() != TYPE_TRANSFORM)
+    return false;
+
+  /* Check to see that both frames are part of the same content. */
+  if (aItem->Frame()->GetContent() != mFrame->GetContent())
+    return false;
+
+  if (aItem->GetClip() != GetClip())
+    return false;
+
+  if (aItem->ScrollClip() != ScrollClip())
+    return false;
+
+  /* Now, move everything over to this frame and signal that
+   * we merged things!
+   */
+  mStoredList.MergeFromTrackingMergedFrames(&static_cast<nsDisplayTransform*>(aItem)->mStoredList);
+  return true;
+}
+
+#endif
+
+/* TransformRect takes in as parameters a rectangle (in app space) and returns
+ * the smallest rectangle (in app space) containing the transformed image of
+ * that rectangle.  That is, it takes the four corners of the rectangle,
+ * transforms them according to the matrix associated with the specified frame,
+ * then returns the smallest rectangle containing the four transformed points.
+ *
+ * @param aUntransformedBounds The rectangle (in app units) to transform.
+ * @param aFrame The frame whose transformation should be applied.
+ * @param aOrigin The delta from the frame origin to the coordinate space origin
+ * @param aBoundsOverride (optional) Force the frame bounds to be the
+ *        specified bounds.
+ * @return The smallest rectangle containing the image of the transformed
+ *         rectangle.
+ */
+nsRect nsDisplayTransform::TransformRect(const nsRect &aUntransformedBounds,
+                                         const nsIFrame* aFrame,
+                                         const nsRect* aBoundsOverride)
+{
+  NS_PRECONDITION(aFrame, "Can't take the transform based on a null frame!");
+
+  float factor = aFrame->PresContext()->AppUnitsPerDevPixel();
+
+  uint32_t flags = INCLUDE_PERSPECTIVE|OFFSET_BY_ORIGIN|INCLUDE_PRESERVE3D_ANCESTORS;
+  return nsLayoutUtils::MatrixTransformRect
+    (aUntransformedBounds,
+     GetResultingTransformMatrix(aFrame, nsPoint(0, 0), factor, flags, aBoundsOverride),
+     factor);
+}
+
+bool nsDisplayTransform::UntransformRect(const nsRect &aTransformedBounds,
+                                         const nsRect &aChildBounds,
+                                         const nsIFrame* aFrame,
+                                         nsRect *aOutRect)
+{
+  NS_PRECONDITION(aFrame, "Can't take the transform based on a null frame!");
+
+  float factor = aFrame->PresContext()->AppUnitsPerDevPixel();
+
+  uint32_t flags = INCLUDE_PERSPECTIVE|OFFSET_BY_ORIGIN|INCLUDE_PRESERVE3D_ANCESTORS;
+
+  Matrix4x4 transform = GetResultingTransformMatrix(aFrame, nsPoint(0, 0), factor, flags);
+  if (transform.IsSingular()) {
+    return false;
+  }
+
+  RectDouble result(NSAppUnitsToFloatPixels(aTransformedBounds.x, factor),
+                    NSAppUnitsToFloatPixels(aTransformedBounds.y, factor),
+                    NSAppUnitsToFloatPixels(aTransformedBounds.width, factor),
+                    NSAppUnitsToFloatPixels(aTransformedBounds.height, factor));
+
+  RectDouble childGfxBounds(NSAppUnitsToFloatPixels(aChildBounds.x, factor),
+                            NSAppUnitsToFloatPixels(aChildBounds.y, factor),
+                            NSAppUnitsToFloatPixels(aChildBounds.width, factor),
+                            NSAppUnitsToFloatPixels(aChildBounds.height, factor));
+
+  result = transform.Inverse().ProjectRectBounds(result, childGfxBounds);
+  *aOutRect = nsLayoutUtils::RoundGfxRectToAppRect(ThebesRect(result), factor);
+  return true;
+}
+
+bool nsDisplayTransform::UntransformVisibleRect(nsDisplayListBuilder* aBuilder,
+                                                nsRect *aOutRect)
+{
+  const Matrix4x4& matrix = GetTransform();
+  if (matrix.IsSingular())
+    return false;
+
+  // GetTransform always operates in dev pixels.
+  float factor = mFrame->PresContext()->AppUnitsPerDevPixel();
+  RectDouble result(NSAppUnitsToFloatPixels(mVisibleRect.x, factor),
+                    NSAppUnitsToFloatPixels(mVisibleRect.y, factor),
+                    NSAppUnitsToFloatPixels(mVisibleRect.width, factor),
+                    NSAppUnitsToFloatPixels(mVisibleRect.height, factor));
+
+  bool snap;
+  nsRect childBounds = mStoredList.GetBounds(aBuilder, &snap);
+  RectDouble childGfxBounds(NSAppUnitsToFloatPixels(childBounds.x, factor),
+                            NSAppUnitsToFloatPixels(childBounds.y, factor),
+                            NSAppUnitsToFloatPixels(childBounds.width, factor),
+                            NSAppUnitsToFloatPixels(childBounds.height, factor));
+
+  /* We want to untransform the matrix, so invert the transformation first! */
+  result = matrix.Inverse().ProjectRectBounds(result, childGfxBounds);
+
+  *aOutRect = nsLayoutUtils::RoundGfxRectToAppRect(ThebesRect(result), factor);
+
+  return true;
+}
+
+void
+nsDisplayTransform::WriteDebugInfo(std::stringstream& aStream)
+{
+  AppendToString(aStream, GetTransform());
+  if (IsTransformSeparator()) {
+    aStream << " transform-separator";
+  }
+  if (IsLeafOf3DContext()) {
+    aStream << " 3d-context-leaf";
+  }
+  if (mFrame->Extend3DContext()) {
+    aStream << " extends-3d-context";
+  }
+  if (mFrame->Combines3DTransformWithAncestors()) {
+    aStream << " combines-3d-with-ancestors";
+  }
+}
+
+nsDisplayPerspective::nsDisplayPerspective(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aTransformFrame,
+                                           nsIFrame* aPerspectiveFrame,
+                                           nsDisplayList* aList)
+  : nsDisplayItem(aBuilder, aPerspectiveFrame)
+  , mList(aBuilder, aPerspectiveFrame, aList)
+  , mTransformFrame(aTransformFrame)
+  , mIndex(aBuilder->AllocatePerspectiveItemIndex())
+{
+  MOZ_ASSERT(mList.GetChildren()->Count() == 1);
+  MOZ_ASSERT(mList.GetChildren()->GetTop()->GetType() == TYPE_TRANSFORM);
+}
+
+already_AddRefed<Layer>
+nsDisplayPerspective::BuildLayer(nsDisplayListBuilder *aBuilder,
+                                 LayerManager *aManager,
+                                 const ContainerLayerParameters& aContainerParameters)
+{
+  float appUnitsPerPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+
+  Matrix4x4 perspectiveMatrix;
+  DebugOnly<bool> hasPerspective =
+    nsDisplayTransform::ComputePerspectiveMatrix(mTransformFrame, appUnitsPerPixel,
+                                                 perspectiveMatrix);
+  MOZ_ASSERT(hasPerspective, "Why did we create nsDisplayPerspective?");
+
+  /*
+   * ClipListToRange can remove our child after we were created.
+   */
+  if (!mList.GetChildren()->GetTop()) {
+    return nullptr;
+  }
+
+  /*
+   * The resulting matrix is still in the coordinate space of the transformed
+   * frame. Append a translation to the reference frame coordinates.
+   */
+  nsDisplayTransform* transform =
+    static_cast<nsDisplayTransform*>(mList.GetChildren()->GetTop());
+
+  Point3D newOrigin =
+    Point3D(NSAppUnitsToFloatPixels(transform->ToReferenceFrame().x, appUnitsPerPixel),
+            NSAppUnitsToFloatPixels(transform->ToReferenceFrame().y, appUnitsPerPixel),
+            0.0f);
+  Point3D roundedOrigin(NS_round(newOrigin.x),
+                        NS_round(newOrigin.y),
+                        0);
+
+  perspectiveMatrix.PostTranslate(roundedOrigin);
+
+  RefPtr<ContainerLayer> container = aManager->GetLayerBuilder()->
+    BuildContainerLayerFor(aBuilder, aManager, mFrame, this, mList.GetChildren(),
+                           aContainerParameters, &perspectiveMatrix, 0);
+
+  if (!container) {
+    return nullptr;
+  }
+
+  // Sort of a lie, but we want to pretend that the perspective layer extends a 3d context
+  // so that it gets its transform combined with children. Might need a better name that reflects
+  // this use case and isn't specific to preserve-3d.
+  container->SetContentFlags(container->GetContentFlags() | Layer::CONTENT_EXTEND_3D_CONTEXT);
+  container->SetTransformIsPerspective(true);
+
+  return container.forget();
+}
+
+LayerState
+nsDisplayPerspective::GetLayerState(nsDisplayListBuilder* aBuilder,
+                                    LayerManager* aManager,
+                                    const ContainerLayerParameters& aParameters)
+{
+  return LAYER_ACTIVE_FORCE;
+}
+
+int32_t
+nsDisplayPerspective::ZIndex() const
+{
+  return ZIndexForFrame(mTransformFrame);
+}
+
+nsDisplayItemGeometry*
+nsCharClipDisplayItem::AllocateGeometry(nsDisplayListBuilder* aBuilder)
+{
+  return new nsCharClipGeometry(this, aBuilder);
+}
+
+void
+nsCharClipDisplayItem::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                         const nsDisplayItemGeometry* aGeometry,
+                                         nsRegion* aInvalidRegion)
+{
+  const nsCharClipGeometry* geometry = static_cast<const nsCharClipGeometry*>(aGeometry);
+
+  bool snap;
+  nsRect newRect = geometry->mBounds;
+  nsRect oldRect = GetBounds(aBuilder, &snap);
+  if (mVisIStartEdge != geometry->mVisIStartEdge ||
+      mVisIEndEdge != geometry->mVisIEndEdge ||
+      !oldRect.IsEqualInterior(newRect) ||
+      !geometry->mBorderRect.IsEqualInterior(GetBorderRect())) {
+    aInvalidRegion->Or(oldRect, newRect);
+  }
+}
+
+nsDisplaySVGEffects::nsDisplaySVGEffects(nsDisplayListBuilder* aBuilder,
+                                         nsIFrame* aFrame, nsDisplayList* aList,
+                                         bool aHandleOpacity,
+                                         const DisplayItemScrollClip* aScrollClip)
+  : nsDisplayWrapList(aBuilder, aFrame, aList, aScrollClip)
+  , mEffectsBounds(aFrame->GetVisualOverflowRectRelativeToSelf())
+  , mHandleOpacity(aHandleOpacity)
+{
+  MOZ_COUNT_CTOR(nsDisplaySVGEffects);
+}
+
+nsDisplaySVGEffects::nsDisplaySVGEffects(nsDisplayListBuilder* aBuilder,
+                                         nsIFrame* aFrame, nsDisplayList* aList,
+                                         bool aHandleOpacity)
+  : nsDisplayWrapList(aBuilder, aFrame, aList)
+  , mEffectsBounds(aFrame->GetVisualOverflowRectRelativeToSelf())
+  , mHandleOpacity(aHandleOpacity)
+{
+  MOZ_COUNT_CTOR(nsDisplaySVGEffects);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplaySVGEffects::~nsDisplaySVGEffects()
+{
+  MOZ_COUNT_DTOR(nsDisplaySVGEffects);
+}
+#endif
+
+nsRegion nsDisplaySVGEffects::GetOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                                              bool* aSnap)
+{
+  *aSnap = false;
+  return nsRegion();
+}
+
+void
+nsDisplaySVGEffects::HitTest(nsDisplayListBuilder* aBuilder, const nsRect& aRect,
+                             HitTestState* aState, nsTArray<nsIFrame*> *aOutFrames)
+{
+  nsPoint rectCenter(aRect.x + aRect.width / 2, aRect.y + aRect.height / 2);
+  if (nsSVGIntegrationUtils::HitTestFrameForEffects(mFrame,
+      rectCenter - ToReferenceFrame())) {
+    mList.HitTest(aBuilder, aRect, aState, aOutFrames);
+  }
+}
+
+gfxRect
+nsDisplaySVGEffects::BBoxInUserSpace() const
+{
+  return nsSVGUtils::GetBBox(mFrame);
+}
+
+gfxPoint
+nsDisplaySVGEffects::UserSpaceOffset() const
+{
+  return nsSVGUtils::FrameSpaceInCSSPxToUserSpaceOffset(mFrame);
+}
+
+void
+nsDisplaySVGEffects::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                               const nsDisplayItemGeometry* aGeometry,
+                                               nsRegion* aInvalidRegion)
+{
+  const nsDisplaySVGEffectGeometry* geometry =
+    static_cast<const nsDisplaySVGEffectGeometry*>(aGeometry);
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+  if (geometry->mFrameOffsetToReferenceFrame != ToReferenceFrame() ||
+      geometry->mUserSpaceOffset != UserSpaceOffset() ||
+      !geometry->mBBox.IsEqualInterior(BBoxInUserSpace())) {
+    // Filter and mask output can depend on the location of the frame's user
+    // space and on the frame's BBox. We need to invalidate if either of these
+    // change relative to the reference frame.
+    // Invalidations from our inactive layer manager are not enough to catch
+    // some of these cases because filters can produce output even if there's
+    // nothing in the filter input.
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+  }
+}
+
+bool nsDisplaySVGEffects::ValidateSVGFrame()
+{
+  const nsIContent* content = mFrame->GetContent();
+  bool hasSVGLayout = (mFrame->GetStateBits() & NS_FRAME_SVG_LAYOUT);
+  if (hasSVGLayout) {
+    nsISVGChildFrame *svgChildFrame = do_QueryFrame(mFrame);
+    if (!svgChildFrame || !mFrame->GetContent()->IsSVGElement()) {
+      NS_ASSERTION(false, "why?");
+      return false;
+    }
+    if (!static_cast<const nsSVGElement*>(content)->HasValidDimensions()) {
+      return false; // The SVG spec says not to draw filters for this
+    }
+  }
+
+  return true;
+}
+
+static IntRect
+ComputeClipExtsInDeviceSpace(gfxContext& aCtx)
+{
+  gfxContextMatrixAutoSaveRestore matRestore(&aCtx);
+
+  // Get the clip extents in device space.
+  aCtx.SetMatrix(gfxMatrix());
+  gfxRect clippedFrameSurfaceRect = aCtx.GetClipExtents();
+  clippedFrameSurfaceRect.RoundOut();
+
+  IntRect result;
+  ToRect(clippedFrameSurfaceRect).ToIntRect(&result);
+  return mozilla::gfx::Factory::CheckSurfaceSize(result.Size()) ? result
+                                                                : IntRect();
+}
+
+typedef nsSVGIntegrationUtils::PaintFramesParams PaintFramesParams;
+
+static nsPoint
+ComputeOffsetToUserSpace(const PaintFramesParams& aParams)
+{
+  nsIFrame* frame = aParams.frame;
+  nsPoint offsetToBoundingBox = aParams.builder->ToReferenceFrame(frame) -
+                         nsSVGIntegrationUtils::GetOffsetToBoundingBox(frame);
+  if (!frame->IsFrameOfType(nsIFrame::eSVG)) {
+    // Snap the offset if the reference frame is not a SVG frame, since other
+    // frames will be snapped to pixel when rendering.
+    offsetToBoundingBox = nsPoint(
+      frame->PresContext()->RoundAppUnitsToNearestDevPixels(offsetToBoundingBox.x),
+      frame->PresContext()->RoundAppUnitsToNearestDevPixels(offsetToBoundingBox.y));
+  }
+
+  // After applying only "offsetToBoundingBox", aParams.ctx would have its
+  // origin at the top left corner of frame's bounding box (over all
+  // continuations).
+  // However, SVG painting needs the origin to be located at the origin of the
+  // SVG frame's "user space", i.e. the space in which, for example, the
+  // frame's BBox lives.
+  // SVG geometry frames and foreignObject frames apply their own offsets, so
+  // their position is relative to their user space. So for these frame types,
+  // if we want aCtx to be in user space, we first need to subtract the
+  // frame's position so that SVG painting can later add it again and the
+  // frame is painted in the right place.
+  gfxPoint toUserSpaceGfx = nsSVGUtils::FrameSpaceInCSSPxToUserSpaceOffset(frame);
+  nsPoint toUserSpace =
+    nsPoint(nsPresContext::CSSPixelsToAppUnits(float(toUserSpaceGfx.x)),
+            nsPresContext::CSSPixelsToAppUnits(float(toUserSpaceGfx.y)));
+
+  return (offsetToBoundingBox - toUserSpace);
+}
+
+static void
+ComputeMaskGeometry(PaintFramesParams& aParams)
+{
+  // Properties are added lazily and may have been removed by a restyle, so
+  // make sure all applicable ones are set again.
+  nsIFrame* firstFrame =
+    nsLayoutUtils::FirstContinuationOrIBSplitSibling(aParams.frame);
+
+  const nsStyleSVGReset *svgReset = firstFrame->StyleSVGReset();
+
+  nsSVGEffects::EffectProperties effectProperties =
+    nsSVGEffects::GetEffectProperties(firstFrame);
+  nsTArray<nsSVGMaskFrame *> maskFrames = effectProperties.GetMaskFrames();
+
+  if (maskFrames.Length() == 0) {
+    return;
+  }
+
+  gfxContext& ctx = aParams.ctx;
+  nsIFrame* frame = aParams.frame;
+
+  nsPoint offsetToUserSpace = ComputeOffsetToUserSpace(aParams);
+  gfxPoint devPixelOffsetToUserSpace =
+    nsLayoutUtils::PointToGfxPoint(offsetToUserSpace,
+                                   frame->PresContext()->AppUnitsPerDevPixel());
+
+  gfxContextMatrixAutoSaveRestore matSR(&ctx);
+  ctx.SetMatrix(ctx.CurrentMatrix().Translate(devPixelOffsetToUserSpace));
+
+  // Convert boaderArea and dirtyRect to user space.
+  int32_t appUnitsPerDevPixel = frame->PresContext()->AppUnitsPerDevPixel();
+  nsRect userSpaceBorderArea = aParams.borderArea - offsetToUserSpace;
+  nsRect userSpaceDirtyRect = aParams.dirtyRect - offsetToUserSpace;
+
+  // Union all mask layer rectangles in user space.
+  gfxRect maskInUserSpace;
+  for (size_t i = 0; i < maskFrames.Length() ; i++) {
+    nsSVGMaskFrame* maskFrame = maskFrames[i];
+    gfxRect currentMaskSurfaceRect;
+
+    if (maskFrame) {
+      currentMaskSurfaceRect = maskFrame->GetMaskArea(aParams.frame);
+    } else {
+      nsCSSRendering::ImageLayerClipState clipState;
+      nsCSSRendering::GetImageLayerClip(svgReset->mMask.mLayers[i],
+                                       frame,
+                                       *frame->StyleBorder(),
+                                       userSpaceBorderArea,
+                                       userSpaceDirtyRect,
+                                       false, /* aWillPaintBorder */
+                                       appUnitsPerDevPixel,
+                                       &clipState);
+      currentMaskSurfaceRect = clipState.mDirtyRectGfx;
+    }
+
+    maskInUserSpace = maskInUserSpace.Union(currentMaskSurfaceRect);
+  }
+
+  ctx.Save();
+
+  if (!maskInUserSpace.IsEmpty()) {
+    ctx.Clip(maskInUserSpace);
+  }
+
+  IntRect result = ComputeClipExtsInDeviceSpace(ctx);
+  ctx.Restore();
+
+  aParams.maskRect = result;
+}
+
+nsDisplayMask::nsDisplayMask(nsDisplayListBuilder* aBuilder,
+                             nsIFrame* aFrame, nsDisplayList* aList,
+                             bool aHandleOpacity,
+                             const DisplayItemScrollClip* aScrollClip)
+  : nsDisplaySVGEffects(aBuilder, aFrame, aList, aHandleOpacity, aScrollClip)
+{
+  MOZ_COUNT_CTOR(nsDisplayMask);
+
+  nsPresContext* presContext = mFrame->PresContext();
+  uint32_t flags = aBuilder->GetBackgroundPaintFlags() |
+                   nsCSSRendering::PAINTBG_MASK_IMAGE;
+  const nsStyleSVGReset *svgReset = aFrame->StyleSVGReset();
+  NS_FOR_VISIBLE_IMAGE_LAYERS_BACK_TO_FRONT(i, svgReset->mMask) {
+    bool isTransformedFixed;
+    nsBackgroundLayerState state =
+      nsCSSRendering::PrepareImageLayer(presContext, aFrame, flags,
+                                        mFrame->GetRectRelativeToSelf(),
+                                        mFrame->GetRectRelativeToSelf(),
+                                        svgReset->mMask.mLayers[i],
+                                        &isTransformedFixed);
+    mDestRects.AppendElement(state.mDestArea);
+  }
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayMask::~nsDisplayMask()
+{
+  MOZ_COUNT_DTOR(nsDisplayMask);
+}
+#endif
+
+bool nsDisplayMask::TryMerge(nsDisplayItem* aItem)
+{
+  if (aItem->GetType() != TYPE_MASK)
+    return false;
+
+  // items for the same content element should be merged into a single
+  // compositing group
+  // aItem->GetUnderlyingFrame() returns non-null because it's nsDisplaySVGEffects
+  if (aItem->Frame()->GetContent() != mFrame->GetContent()) {
+    return false;
+  }
+  if (aItem->GetClip() != GetClip()) {
+    return false;
+  }
+  if (aItem->ScrollClip() != ScrollClip()) {
+    return false;
+  }
+
+  // Do not merge if mFrame has mask. Continuation frames should apply mask
+  // independently(just like nsDisplayBackgroundImage).
+  const nsStyleSVGReset *style = mFrame->StyleSVGReset();
+  if (style->mMask.HasLayerWithImage()) {
+    return false;
+  }
+
+  nsDisplayMask* other = static_cast<nsDisplayMask*>(aItem);
+  MergeFromTrackingMergedFrames(other);
+  mEffectsBounds.UnionRect(mEffectsBounds,
+    other->mEffectsBounds + other->mFrame->GetOffsetTo(mFrame));
+
+  return true;
+}
+
+already_AddRefed<Layer>
+nsDisplayMask::BuildLayer(nsDisplayListBuilder* aBuilder,
+                          LayerManager* aManager,
+                          const ContainerLayerParameters& aContainerParameters)
+{
+  if (!ValidateSVGFrame()) {
+    return nullptr;
+  }
+
+  if (mFrame->StyleEffects()->mOpacity == 0.0f && mHandleOpacity) {
+    return nullptr;
+  }
+
+  nsIFrame* firstFrame =
+    nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+  nsSVGEffects::EffectProperties effectProperties =
+    nsSVGEffects::GetEffectProperties(firstFrame);
+
+  bool isOK = effectProperties.HasNoFilterOrHasValidFilter();
+  effectProperties.GetClipPathFrame(&isOK);
+
+  if (!isOK) {
+    return nullptr;
+  }
+
+  RefPtr<ContainerLayer> container = aManager->GetLayerBuilder()->
+    BuildContainerLayerFor(aBuilder, aManager, mFrame, this, &mList,
+                           aContainerParameters, nullptr);
+
+  return container.forget();
+}
+
+bool
+nsDisplayMask::PaintMask(nsDisplayListBuilder* aBuilder,
+                         gfxContext* aMaskContext)
+{
+  MOZ_ASSERT(aMaskContext->GetDrawTarget()->GetFormat() == SurfaceFormat::A8);
+
+  nsRect borderArea = nsRect(ToReferenceFrame(), mFrame->GetSize());
+  nsSVGIntegrationUtils::PaintFramesParams params(*aMaskContext,
+                                                  mFrame,  mVisibleRect,
+                                                  borderArea, aBuilder,
+                                                  nullptr,
+                                                  mHandleOpacity);
+  ComputeMaskGeometry(params);
+  image::DrawResult result = nsSVGIntegrationUtils::PaintMask(params);
+
+  nsDisplayMaskGeometry::UpdateDrawResult(this, result);
+  return (result == image::DrawResult::SUCCESS) ? true : false;
+}
+
+LayerState
+nsDisplayMask::GetLayerState(nsDisplayListBuilder* aBuilder,
+                             LayerManager* aManager,
+                             const ContainerLayerParameters& aParameters)
+{
+  if (ShouldPaintOnMaskLayer(aManager)) {
+    return RequiredLayerStateForChildren(aBuilder, aManager, aParameters,
+                                         mList, GetAnimatedGeometryRoot());
+  }
+
+  return LAYER_SVG_EFFECTS;
+}
+
+bool nsDisplayMask::ShouldPaintOnMaskLayer(LayerManager* aManager)
+{
+  if (!aManager->IsCompositingCheap()) {
+    return false;
+  }
+
+  nsSVGUtils::MaskUsage maskUsage;
+  nsSVGUtils::DetermineMaskUsage(mFrame, mHandleOpacity, maskUsage);
+
+  if (!maskUsage.shouldGenerateMaskLayer ||
+      maskUsage.opacity != 1.0 || maskUsage.shouldApplyClipPath ||
+      maskUsage.shouldApplyBasicShape ||
+      maskUsage.shouldGenerateClipMaskLayer) {
+    return false;
+  }
+
+  if (!nsSVGIntegrationUtils::IsMaskResourceReady(mFrame)) {
+    return false;
+  }
+
+  // XXX temporary disable drawing SVG mask onto mask layer before bug 1313877
+  // been fixed.
+  nsIFrame* firstFrame =
+    nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+  nsSVGEffects::EffectProperties effectProperties =
+    nsSVGEffects::GetEffectProperties(firstFrame);
+  nsTArray<nsSVGMaskFrame *> maskFrames = effectProperties.GetMaskFrames();
+  for (size_t i = 0; i < maskFrames.Length() ; i++) {
+    nsSVGMaskFrame *maskFrame = maskFrames[i];
+    if (maskFrame) {
+      return false; // Found SVG mask.
+    }
+  }
+
+  if (gfxPrefs::DrawMaskLayer()) {
+    return false;
+  }
+
+  return true;
+}
+
+bool nsDisplayMask::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                      nsRegion* aVisibleRegion)
+{
+  // Our children may be made translucent or arbitrarily deformed so we should
+  // not allow them to subtract area from aVisibleRegion.
+  nsRegion childrenVisible(mVisibleRect);
+  nsRect r = mVisibleRect.Intersect(mList.GetBounds(aBuilder));
+  mList.ComputeVisibilityForSublist(aBuilder, &childrenVisible, r);
+  return true;
+}
+
+void
+nsDisplayMask::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                         const nsDisplayItemGeometry* aGeometry,
+                                         nsRegion* aInvalidRegion)
+{
+  nsDisplaySVGEffects::ComputeInvalidationRegion(aBuilder, aGeometry,
+                                                 aInvalidRegion);
+
+  const nsDisplayMaskGeometry* geometry =
+    static_cast<const nsDisplayMaskGeometry*>(aGeometry);
+  bool snap;
+  nsRect bounds = GetBounds(aBuilder, &snap);
+
+  if (mDestRects.Length() != geometry->mDestRects.Length()) {
+    aInvalidRegion->Or(bounds, geometry->mBounds);
+  } else {
+    for (size_t i = 0; i < mDestRects.Length(); i++) {
+      if (!mDestRects[i].IsEqualInterior(geometry->mDestRects[i])) {
+        aInvalidRegion->Or(bounds, geometry->mBounds);
+        break;
+      }
+    }
+  }
+
+  if (aBuilder->ShouldSyncDecodeImages() &&
+      geometry->ShouldInvalidateToSyncDecodeImages()) {
+    const nsStyleSVGReset *svgReset = mFrame->StyleSVGReset();
+    NS_FOR_VISIBLE_IMAGE_LAYERS_BACK_TO_FRONT(i, svgReset->mMask) {
+      const nsStyleImage& image = svgReset->mMask.mLayers[i].mImage;
+      if (image.GetType() == eStyleImageType_Image ) {
+        aInvalidRegion->Or(*aInvalidRegion, bounds);
+        break;
+      }
+    }
+  }
+}
+
+void
+nsDisplayMask::PaintAsLayer(nsDisplayListBuilder* aBuilder,
+                            nsRenderingContext* aCtx,
+                            LayerManager* aManager)
+{
+  MOZ_ASSERT(!ShouldPaintOnMaskLayer(aManager));
+
+  nsRect borderArea = nsRect(ToReferenceFrame(), mFrame->GetSize());
+  nsSVGIntegrationUtils::PaintFramesParams params(*aCtx->ThebesContext(),
+                                                  mFrame,  mVisibleRect,
+                                                  borderArea, aBuilder,
+                                                  aManager,
+                                                  mHandleOpacity);
+
+  // Clip the drawing target by mVisibleRect, which contains the visible
+  // region of the target frame and its out-of-flow and inflow descendants.
+  gfxContext* context = aCtx->ThebesContext();
+
+  Rect bounds =
+    NSRectToRect(mVisibleRect, mFrame->PresContext()->AppUnitsPerDevPixel());
+  bounds.RoundOut();
+  context->Clip(bounds);
+
+  ComputeMaskGeometry(params);
+
+  image::DrawResult result =
+    nsSVGIntegrationUtils::PaintMaskAndClipPath(params);
+
+  context->PopClip();
+
+  nsDisplayMaskGeometry::UpdateDrawResult(this, result);
+}
+
+#ifdef MOZ_DUMP_PAINTING
+void
+nsDisplayMask::PrintEffects(nsACString& aTo)
+{
+  nsIFrame* firstFrame =
+    nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+  nsSVGEffects::EffectProperties effectProperties =
+    nsSVGEffects::GetEffectProperties(firstFrame);
+  bool isOK = true;
+  nsSVGClipPathFrame *clipPathFrame = effectProperties.GetClipPathFrame(&isOK);
+  bool first = true;
+  aTo += " effects=(";
+  if (mFrame->StyleEffects()->mOpacity != 1.0f && mHandleOpacity) {
+    first = false;
+    aTo += nsPrintfCString("opacity(%f)", mFrame->StyleEffects()->mOpacity);
+  }
+  if (clipPathFrame) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += nsPrintfCString("clip(%s)", clipPathFrame->IsTrivial() ? "trivial" : "non-trivial");
+    first = false;
+  }
+  const nsStyleSVGReset *style = mFrame->StyleSVGReset();
+  if (style->HasClipPath() && !clipPathFrame) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += "clip(basic-shape)";
+    first = false;
+  }
+
+  if (effectProperties.GetFirstMaskFrame()) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += "mask";
+  }
+  aTo += ")";
+}
+#endif
+
+nsDisplayFilter::nsDisplayFilter(nsDisplayListBuilder* aBuilder,
+                                 nsIFrame* aFrame, nsDisplayList* aList,
+                                 bool aHandleOpacity)
+  : nsDisplaySVGEffects(aBuilder, aFrame, aList, aHandleOpacity)
+{
+  MOZ_COUNT_CTOR(nsDisplayFilter);
+}
+
+#ifdef NS_BUILD_REFCNT_LOGGING
+nsDisplayFilter::~nsDisplayFilter()
+{
+  MOZ_COUNT_DTOR(nsDisplayFilter);
+}
+#endif
+
+already_AddRefed<Layer>
+nsDisplayFilter::BuildLayer(nsDisplayListBuilder* aBuilder,
+                           LayerManager* aManager,
+                           const ContainerLayerParameters& aContainerParameters)
+{
+  if (!ValidateSVGFrame()) {
+    return nullptr;
+  }
+
+  if (mFrame->StyleEffects()->mOpacity == 0.0f && mHandleOpacity) {
+    return nullptr;
+  }
+
+  nsIFrame* firstFrame =
+    nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+  nsSVGEffects::EffectProperties effectProperties =
+    nsSVGEffects::GetEffectProperties(firstFrame);
+
+  ContainerLayerParameters newContainerParameters = aContainerParameters;
+  if (effectProperties.HasValidFilter()) {
+    newContainerParameters.mDisableSubpixelAntialiasingInDescendants = true;
+  }
+
+  RefPtr<ContainerLayer> container = aManager->GetLayerBuilder()->
+    BuildContainerLayerFor(aBuilder, aManager, mFrame, this, &mList,
+                           newContainerParameters, nullptr);
+
+  return container.forget();
+}
+
+bool nsDisplayFilter::TryMerge(nsDisplayItem* aItem)
+{
+  if (aItem->GetType() != TYPE_FILTER) {
+    return false;
+  }
+
+  // items for the same content element should be merged into a single
+  // compositing group.
+  // aItem->Frame() returns non-null because it's nsDisplayFilter
+  if (aItem->Frame()->GetContent() != mFrame->GetContent()) {
+    return false;
+  }
+  if (aItem->GetClip() != GetClip()) {
+    return false;
+  }
+  if (aItem->ScrollClip() != ScrollClip()) {
+    return false;
+  }
+
+  nsDisplayFilter* other = static_cast<nsDisplayFilter*>(aItem);
+  MergeFromTrackingMergedFrames(other);
+  mEffectsBounds.UnionRect(mEffectsBounds,
+    other->mEffectsBounds + other->mFrame->GetOffsetTo(mFrame));
+
+  return true;
+}
+
+LayerState
+nsDisplayFilter::GetLayerState(nsDisplayListBuilder* aBuilder,
+                               LayerManager* aManager,
+                               const ContainerLayerParameters& aParameters)
+{
+  return LAYER_SVG_EFFECTS;
+}
+
+bool nsDisplayFilter::ComputeVisibility(nsDisplayListBuilder* aBuilder,
+                                        nsRegion* aVisibleRegion)
+{
+  nsPoint offset = ToReferenceFrame();
+  nsRect dirtyRect =
+    nsSVGIntegrationUtils::GetRequiredSourceForInvalidArea(mFrame,
+                                                           mVisibleRect - offset) +
+    offset;
+
+  // Our children may be made translucent or arbitrarily deformed so we should
+  // not allow them to subtract area from aVisibleRegion.
+  nsRegion childrenVisible(dirtyRect);
+  nsRect r = dirtyRect.Intersect(mList.GetBounds(aBuilder));
+  mList.ComputeVisibilityForSublist(aBuilder, &childrenVisible, r);
+  return true;
+}
+
+void
+nsDisplayFilter::ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
+                                           const nsDisplayItemGeometry* aGeometry,
+                                           nsRegion* aInvalidRegion)
+{
+  nsDisplaySVGEffects::ComputeInvalidationRegion(aBuilder, aGeometry,
+                                                 aInvalidRegion);
+
+  const nsDisplayFilterGeometry* geometry =
+    static_cast<const nsDisplayFilterGeometry*>(aGeometry);
+
+  if (aBuilder->ShouldSyncDecodeImages() &&
+      geometry->ShouldInvalidateToSyncDecodeImages()) {
+    bool snap;
+    nsRect bounds = GetBounds(aBuilder, &snap);
+    aInvalidRegion->Or(*aInvalidRegion, bounds);
+  }
+}
+
+void
+nsDisplayFilter::PaintAsLayer(nsDisplayListBuilder* aBuilder,
+                              nsRenderingContext* aCtx,
+                              LayerManager* aManager)
+{
+  nsRect borderArea = nsRect(ToReferenceFrame(), mFrame->GetSize());
+  nsSVGIntegrationUtils::PaintFramesParams params(*aCtx->ThebesContext(),
+                                                  mFrame,  mVisibleRect,
+                                                  borderArea, aBuilder,
+                                                  aManager,
+                                                  mHandleOpacity);
+
+  image::DrawResult result = nsSVGIntegrationUtils::PaintFilter(params);
+  nsDisplayFilterGeometry::UpdateDrawResult(this, result);
+}
+
+#ifdef MOZ_DUMP_PAINTING
+void
+nsDisplayFilter::PrintEffects(nsACString& aTo)
+{
+  nsIFrame* firstFrame =
+    nsLayoutUtils::FirstContinuationOrIBSplitSibling(mFrame);
+  nsSVGEffects::EffectProperties effectProperties =
+    nsSVGEffects::GetEffectProperties(firstFrame);
+  bool first = true;
+  aTo += " effects=(";
+  if (mFrame->StyleEffects()->mOpacity != 1.0f && mHandleOpacity) {
+    first = false;
+    aTo += nsPrintfCString("opacity(%f)", mFrame->StyleEffects()->mOpacity);
+  }
+  if (effectProperties.HasValidFilter()) {
+    if (!first) {
+      aTo += ", ";
+    }
+    aTo += "filter";
+  }
+  aTo += ")";
+}
+#endif
+
+namespace mozilla {
+
+uint32_t PaintTelemetry::sPaintLevel = 0;
+uint32_t PaintTelemetry::sMetricLevel = 0;
+EnumeratedArray<PaintTelemetry::Metric,
+                PaintTelemetry::Metric::COUNT,
+                double> PaintTelemetry::sMetrics;
+
+PaintTelemetry::AutoRecordPaint::AutoRecordPaint()
+{
+  // Don't record nested paints.
+  if (sPaintLevel++ > 0) {
+    return;
+  }
+
+  // Reset metrics for a new paint.
+  for (auto& metric : sMetrics) {
+    metric = 0.0;
+  }
+  mStart = TimeStamp::Now();
+}
+
+PaintTelemetry::AutoRecordPaint::~AutoRecordPaint()
+{
+  MOZ_ASSERT(sPaintLevel != 0);
+  if (--sPaintLevel > 0) {
+    return;
+  }
+
+  // If we're in multi-process mode, don't include paint times for the parent
+  // process.
+  if (gfxVars::BrowserTabsRemoteAutostart() && XRE_IsParentProcess()) {
+    return;
+  }
+
+  double totalMs = (TimeStamp::Now() - mStart).ToMilliseconds();
+
+  // Record the total time.
+  Telemetry::Accumulate(Telemetry::CONTENT_PAINT_TIME, static_cast<uint32_t>(totalMs));
+
+  // If the total time was >= 16ms, then it's likely we missed a frame due to
+  // painting. In this case we'll gather some detailed metrics below.
+  if (totalMs <= 16.0) {
+    return;
+  }
+
+  auto record = [=](const char* aKey, double aDurationMs) -> void {
+    MOZ_ASSERT(aDurationMs <= totalMs);
+
+    uint32_t amount = static_cast<int32_t>((aDurationMs / totalMs) * 100.0);
+
+    nsDependentCString key(aKey);
+    Telemetry::Accumulate(Telemetry::CONTENT_LARGE_PAINT_PHASE_WEIGHT, key, amount);
+  };
+
+  double dlMs = sMetrics[Metric::DisplayList];
+  double flbMs = sMetrics[Metric::Layerization];
+  double rMs = sMetrics[Metric::Rasterization];
+
+  // Record all permutations since aggregation makes it difficult to
+  // correlate. For example we can't derive "flb+r" from "dl" because we
+  // don't know the total time associated with a bucket entry. So we just
+  // play it safe and include everything. We can however derive "other" time
+  // from the final permutation.
+  record("dl", dlMs);
+  record("flb", flbMs);
+  record("r", rMs);
+  record("dl,flb", dlMs + flbMs);
+  record("dl,r", dlMs + rMs);
+  record("flb,r", flbMs + rMs);
+  record("dl,flb,r", dlMs + flbMs + rMs);
+}
+
+PaintTelemetry::AutoRecord::AutoRecord(Metric aMetric)
+ : mMetric(aMetric)
+{
+  // Don't double-record anything nested.
+  if (sMetricLevel++ > 0) {
+    return;
+  }
+
+  // Don't record inside nested paints, or outside of paints.
+  if (sPaintLevel != 1) {
+    return;
+  }
+
+  mStart = TimeStamp::Now();
+}
+
+PaintTelemetry::AutoRecord::~AutoRecord()
+{
+  MOZ_ASSERT(sMetricLevel != 0);
+
+  sMetricLevel--;
+  if (mStart.IsNull()) {
+    return;
+  }
+
+  sMetrics[mMetric] += (TimeStamp::Now() - mStart).ToMilliseconds();
+}
+
+} // namespace mozilla