Add m-esr52 at 52.6.0

1 files changed, 6378 insertions, 0 deletions

diff --git a/layout/base/FrameLayerBuilder.cpp b/layout/base/FrameLayerBuilder.cpp
new file mode 100644
index 000000000..9269c2ab6
--- /dev/null
+++ b/layout/base/FrameLayerBuilder.cpp
@@ -0,0 +1,6378 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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/. */
+
+#include "mozilla/DebugOnly.h"
+
+#include "FrameLayerBuilder.h"
+
+#include "mozilla/LookAndFeel.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/dom/ProfileTimelineMarkerBinding.h"
+#include "mozilla/gfx/Matrix.h"
+#include "ActiveLayerTracker.h"
+#include "BasicLayers.h"
+#include "DisplayItemScrollClip.h"
+#include "ImageContainer.h"
+#include "ImageLayers.h"
+#include "LayerTreeInvalidation.h"
+#include "Layers.h"
+#include "LayerUserData.h"
+#include "MaskLayerImageCache.h"
+#include "UnitTransforms.h"
+#include "Units.h"
+#include "gfx2DGlue.h"
+#include "gfxEnv.h"
+#include "gfxUtils.h"
+#include "nsAutoPtr.h"
+#include "nsAnimationManager.h"
+#include "nsDisplayList.h"
+#include "nsDocShell.h"
+#include "nsIScrollableFrame.h"
+#include "nsImageFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsPresContext.h"
+#include "nsPrintfCString.h"
+#include "nsRenderingContext.h"
+#include "nsSVGIntegrationUtils.h"
+#include "nsTransitionManager.h"
+#include "mozilla/LayerTimelineMarker.h"
+
+#include "mozilla/EffectCompositor.h"
+#include "mozilla/Move.h"
+#include "mozilla/ReverseIterator.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Tools.h"
+#include "mozilla/layers/ShadowLayers.h"
+#include "mozilla/layers/TextureClient.h"
+#include "mozilla/layers/TextureWrapperImage.h"
+#include "mozilla/Unused.h"
+#include "GeckoProfiler.h"
+#include "LayersLogging.h"
+#include "gfxPrefs.h"
+
+#include <algorithm>
+
+using namespace mozilla::layers;
+using namespace mozilla::gfx;
+
+namespace mozilla {
+
+class PaintedDisplayItemLayerUserData;
+
+static nsTHashtable<nsPtrHashKey<FrameLayerBuilder::DisplayItemData>>* sAliveDisplayItemDatas;
+
+/**
+ * The address of gPaintedDisplayItemLayerUserData is used as the user
+ * data key for PaintedLayers created by FrameLayerBuilder.
+ * It identifies PaintedLayers used to draw non-layer content, which are
+ * therefore eligible for recycling. We want display items to be able to
+ * create their own dedicated PaintedLayers in BuildLayer, if necessary,
+ * and we wouldn't want to accidentally recycle those.
+ * The user data is a PaintedDisplayItemLayerUserData.
+ */
+uint8_t gPaintedDisplayItemLayerUserData;
+/**
+ * The address of gColorLayerUserData is used as the user
+ * data key for ColorLayers created by FrameLayerBuilder.
+ * The user data is null.
+ */
+uint8_t gColorLayerUserData;
+/**
+ * The address of gImageLayerUserData is used as the user
+ * data key for ImageLayers created by FrameLayerBuilder.
+ * The user data is null.
+ */
+uint8_t gImageLayerUserData;
+/**
+ * The address of gLayerManagerUserData is used as the user
+ * data key for retained LayerManagers managed by FrameLayerBuilder.
+ * The user data is a LayerManagerData.
+ */
+uint8_t gLayerManagerUserData;
+/**
+ * The address of gMaskLayerUserData is used as the user
+ * data key for mask layers managed by FrameLayerBuilder.
+ * The user data is a MaskLayerUserData.
+ */
+uint8_t gMaskLayerUserData;
+/**
+ * The address of gCSSMaskLayerUserData is used as the user
+ * data key for mask layers of css masking managed by FrameLayerBuilder.
+ * The user data is a CSSMaskLayerUserData.
+ */
+uint8_t gCSSMaskLayerUserData;
+
+// a global cache of image containers used for mask layers
+static MaskLayerImageCache* gMaskLayerImageCache = nullptr;
+
+static inline MaskLayerImageCache* GetMaskLayerImageCache()
+{
+  if (!gMaskLayerImageCache) {
+    gMaskLayerImageCache = new MaskLayerImageCache();
+  }
+
+  return gMaskLayerImageCache;
+}
+
+FrameLayerBuilder::FrameLayerBuilder()
+  : mRetainingManager(nullptr)
+  , mDetectedDOMModification(false)
+  , mInvalidateAllLayers(false)
+  , mInLayerTreeCompressionMode(false)
+  , mContainerLayerGeneration(0)
+  , mMaxContainerLayerGeneration(0)
+{
+  MOZ_COUNT_CTOR(FrameLayerBuilder);
+}
+
+FrameLayerBuilder::~FrameLayerBuilder()
+{
+  GetMaskLayerImageCache()->Sweep();
+  MOZ_COUNT_DTOR(FrameLayerBuilder);
+}
+
+FrameLayerBuilder::DisplayItemData::DisplayItemData(LayerManagerData* aParent, uint32_t aKey,
+                                                    Layer* aLayer, nsIFrame* aFrame)
+
+  : mParent(aParent)
+  , mLayer(aLayer)
+  , mDisplayItemKey(aKey)
+  , mItem(nullptr)
+  , mUsed(true)
+  , mIsInvalid(false)
+{
+  MOZ_COUNT_CTOR(FrameLayerBuilder::DisplayItemData);
+
+  if (!sAliveDisplayItemDatas) {
+    sAliveDisplayItemDatas = new nsTHashtable<nsPtrHashKey<FrameLayerBuilder::DisplayItemData>>();
+  }
+  MOZ_RELEASE_ASSERT(!sAliveDisplayItemDatas->Contains(this));
+  sAliveDisplayItemDatas->PutEntry(this);
+
+  MOZ_RELEASE_ASSERT(mLayer);
+  if (aFrame) {
+    AddFrame(aFrame);
+  }
+
+}
+
+void
+FrameLayerBuilder::DisplayItemData::AddFrame(nsIFrame* aFrame)
+{
+  MOZ_RELEASE_ASSERT(mLayer);
+  mFrameList.AppendElement(aFrame);
+
+  nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(FrameLayerBuilder::LayerManagerDataProperty());
+  if (!array) {
+    array = new nsTArray<DisplayItemData*>();
+    aFrame->Properties().Set(FrameLayerBuilder::LayerManagerDataProperty(), array);
+  }
+  array->AppendElement(this);
+}
+
+void
+FrameLayerBuilder::DisplayItemData::RemoveFrame(nsIFrame* aFrame)
+{
+  MOZ_RELEASE_ASSERT(mLayer);
+  bool result = mFrameList.RemoveElement(aFrame);
+  MOZ_RELEASE_ASSERT(result, "Can't remove a frame that wasn't added!");
+
+  nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(FrameLayerBuilder::LayerManagerDataProperty());
+  MOZ_RELEASE_ASSERT(array, "Must be already stored on the frame!");
+  array->RemoveElement(this);
+}
+
+void
+FrameLayerBuilder::DisplayItemData::EndUpdate()
+{
+  MOZ_RELEASE_ASSERT(mLayer);
+  MOZ_ASSERT(!mItem);
+  mIsInvalid = false;
+  mUsed = false;
+}
+
+void
+FrameLayerBuilder::DisplayItemData::EndUpdate(nsAutoPtr<nsDisplayItemGeometry> aGeometry)
+{
+  MOZ_RELEASE_ASSERT(mLayer);
+  MOZ_ASSERT(mItem);
+  MOZ_ASSERT(mGeometry || aGeometry);
+
+  if (aGeometry) {
+    mGeometry = aGeometry;
+  }
+  mClip = mItem->GetClip();
+  mFrameListChanges.Clear();
+
+  mItem = nullptr;
+  EndUpdate();
+}
+
+void
+FrameLayerBuilder::DisplayItemData::BeginUpdate(Layer* aLayer, LayerState aState,
+                                                uint32_t aContainerLayerGeneration,
+                                                nsDisplayItem* aItem /* = nullptr */)
+{
+  MOZ_RELEASE_ASSERT(mLayer);
+  MOZ_RELEASE_ASSERT(aLayer);
+  mLayer = aLayer;
+  mOptLayer = nullptr;
+  mInactiveManager = nullptr;
+  mLayerState = aState;
+  mContainerLayerGeneration = aContainerLayerGeneration;
+  mUsed = true;
+
+  if (aLayer->AsPaintedLayer()) {
+    mItem = aItem;
+  }
+
+  if (!aItem) {
+    return;
+  }
+
+  // We avoid adding or removing element unnecessarily
+  // since we have to modify userdata each time
+  AutoTArray<nsIFrame*, 4> copy(mFrameList);
+  if (!copy.RemoveElement(aItem->Frame())) {
+    AddFrame(aItem->Frame());
+    mFrameListChanges.AppendElement(aItem->Frame());
+  }
+
+  AutoTArray<nsIFrame*,4> mergedFrames;
+  aItem->GetMergedFrames(&mergedFrames);
+  for (uint32_t i = 0; i < mergedFrames.Length(); ++i) {
+    if (!copy.RemoveElement(mergedFrames[i])) {
+      AddFrame(mergedFrames[i]);
+      mFrameListChanges.AppendElement(mergedFrames[i]);
+    }
+  }
+
+  for (uint32_t i = 0; i < copy.Length(); i++) {
+    RemoveFrame(copy[i]);
+    mFrameListChanges.AppendElement(copy[i]);
+  }
+}
+
+static const nsIFrame* sDestroyedFrame = nullptr;
+FrameLayerBuilder::DisplayItemData::~DisplayItemData()
+{
+  MOZ_COUNT_DTOR(FrameLayerBuilder::DisplayItemData);
+  MOZ_RELEASE_ASSERT(mLayer);
+  for (uint32_t i = 0; i < mFrameList.Length(); i++) {
+    nsIFrame* frame = mFrameList[i];
+    if (frame == sDestroyedFrame) {
+      continue;
+    }
+    nsTArray<DisplayItemData*> *array =
+      reinterpret_cast<nsTArray<DisplayItemData*>*>(frame->Properties().Get(LayerManagerDataProperty()));
+    array->RemoveElement(this);
+  }
+
+  MOZ_RELEASE_ASSERT(sAliveDisplayItemDatas && sAliveDisplayItemDatas->Contains(this));
+  sAliveDisplayItemDatas->RemoveEntry(this);
+  if (sAliveDisplayItemDatas->Count() == 0) {
+    delete sAliveDisplayItemDatas;
+    sAliveDisplayItemDatas = nullptr;
+  }
+}
+
+void
+FrameLayerBuilder::DisplayItemData::ClearAnimationCompositorState()
+{
+  if (mDisplayItemKey != nsDisplayItem::TYPE_TRANSFORM &&
+      mDisplayItemKey != nsDisplayItem::TYPE_OPACITY) {
+    return;
+  }
+
+  for (nsIFrame* frame : mFrameList) {
+    nsCSSPropertyID prop = mDisplayItemKey == nsDisplayItem::TYPE_TRANSFORM ?
+      eCSSProperty_transform : eCSSProperty_opacity;
+    EffectCompositor::ClearIsRunningOnCompositor(frame, prop);
+  }
+}
+
+const nsTArray<nsIFrame*>&
+FrameLayerBuilder::DisplayItemData::GetFrameListChanges()
+{
+  return mFrameListChanges;
+}
+
+/**
+ * This is the userdata we associate with a layer manager.
+ */
+class LayerManagerData : public LayerUserData {
+public:
+  explicit LayerManagerData(LayerManager *aManager)
+    : mLayerManager(aManager)
+#ifdef DEBUG_DISPLAY_ITEM_DATA
+    , mParent(nullptr)
+#endif
+    , mInvalidateAllLayers(false)
+  {
+    MOZ_COUNT_CTOR(LayerManagerData);
+  }
+  ~LayerManagerData() {
+    MOZ_COUNT_DTOR(LayerManagerData);
+  }
+
+#ifdef DEBUG_DISPLAY_ITEM_DATA
+  void Dump(const char *aPrefix = "") {
+    printf_stderr("%sLayerManagerData %p\n", aPrefix, this);
+
+    for (auto iter = mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
+      FrameLayerBuilder::DisplayItemData* data = iter.Get()->GetKey();
+
+      nsAutoCString prefix;
+      prefix += aPrefix;
+      prefix += "  ";
+
+      const char* layerState;
+      switch (data->mLayerState) {
+      case LAYER_NONE:
+        layerState = "LAYER_NONE"; break;
+      case LAYER_INACTIVE:
+        layerState = "LAYER_INACTIVE"; break;
+      case LAYER_ACTIVE:
+        layerState = "LAYER_ACTIVE"; break;
+      case LAYER_ACTIVE_FORCE:
+        layerState = "LAYER_ACTIVE_FORCE"; break;
+      case LAYER_ACTIVE_EMPTY:
+        layerState = "LAYER_ACTIVE_EMPTY"; break;
+      case LAYER_SVG_EFFECTS:
+        layerState = "LAYER_SVG_EFFECTS"; break;
+      }
+      uint32_t mask = (1 << nsDisplayItem::TYPE_BITS) - 1;
+
+      nsAutoCString str;
+      str += prefix;
+      str += nsPrintfCString("Frame %p ", data->mFrameList[0]);
+      str += nsDisplayItem::DisplayItemTypeName(static_cast<nsDisplayItem::Type>(data->mDisplayItemKey & mask));
+      if ((data->mDisplayItemKey >> nsDisplayItem::TYPE_BITS)) {
+        str += nsPrintfCString("(%i)", data->mDisplayItemKey >> nsDisplayItem::TYPE_BITS);
+      }
+      str += nsPrintfCString(", %s, Layer %p", layerState, data->mLayer.get());
+      if (data->mOptLayer) {
+        str += nsPrintfCString(", OptLayer %p", data->mOptLayer.get());
+      }
+      if (data->mInactiveManager) {
+        str += nsPrintfCString(", InactiveLayerManager %p", data->mInactiveManager.get());
+      }
+      str += "\n";
+
+      printf_stderr("%s", str.get());
+
+      if (data->mInactiveManager) {
+        prefix += "  ";
+        printf_stderr("%sDumping inactive layer info:\n", prefix.get());
+        LayerManagerData* lmd = static_cast<LayerManagerData*>
+          (data->mInactiveManager->GetUserData(&gLayerManagerUserData));
+        lmd->Dump(prefix.get());
+      }
+    }
+  }
+#endif
+
+  /**
+   * Tracks which frames have layers associated with them.
+   */
+  LayerManager *mLayerManager;
+#ifdef DEBUG_DISPLAY_ITEM_DATA
+  LayerManagerData *mParent;
+#endif
+  nsTHashtable<nsRefPtrHashKey<FrameLayerBuilder::DisplayItemData> > mDisplayItems;
+  bool mInvalidateAllLayers;
+};
+
+/* static */ void
+FrameLayerBuilder::DestroyDisplayItemDataFor(nsIFrame* aFrame)
+{
+  FrameProperties props = aFrame->Properties();
+  props.Delete(LayerManagerDataProperty());
+}
+
+struct AssignedDisplayItem
+{
+  AssignedDisplayItem(nsDisplayItem* aItem,
+                      const DisplayItemClip& aClip,
+                      LayerState aLayerState)
+    : mItem(aItem)
+    , mClip(aClip)
+    , mLayerState(aLayerState)
+  {}
+
+  nsDisplayItem* mItem;
+  DisplayItemClip mClip;
+  LayerState mLayerState;
+};
+
+/**
+ * We keep a stack of these to represent the PaintedLayers that are
+ * currently available to have display items added to.
+ * We use a stack here because as much as possible we want to
+ * assign display items to existing PaintedLayers, and to the lowest
+ * PaintedLayer in z-order. This reduces the number of layers and
+ * makes it more likely a display item will be rendered to an opaque
+ * layer, giving us the best chance of getting subpixel AA.
+ */
+class PaintedLayerData {
+public:
+  PaintedLayerData() :
+    mAnimatedGeometryRoot(nullptr),
+    mScrollClip(nullptr),
+    mReferenceFrame(nullptr),
+    mLayer(nullptr),
+    mSolidColor(NS_RGBA(0, 0, 0, 0)),
+    mIsSolidColorInVisibleRegion(false),
+    mFontSmoothingBackgroundColor(NS_RGBA(0,0,0,0)),
+    mSingleItemFixedToViewport(false),
+    mNeedComponentAlpha(false),
+    mForceTransparentSurface(false),
+    mHideAllLayersBelow(false),
+    mOpaqueForAnimatedGeometryRootParent(false),
+    mDisableFlattening(false),
+    mBackfaceHidden(false),
+    mImage(nullptr),
+    mCommonClipCount(-1),
+    mNewChildLayersIndex(-1)
+  {}
+
+#ifdef MOZ_DUMP_PAINTING
+  /**
+   * Keep track of important decisions for debugging.
+   */
+  nsCString mLog;
+
+  #define FLB_LOG_PAINTED_LAYER_DECISION(pld, ...) \
+          if (gfxPrefs::LayersDumpDecision()) { \
+            pld->mLog.AppendPrintf("\t\t\t\t"); \
+            pld->mLog.AppendPrintf(__VA_ARGS__); \
+          }
+#else
+  #define FLB_LOG_PAINTED_LAYER_DECISION(...)
+#endif
+
+  /**
+   * Record that an item has been added to the PaintedLayer, so we
+   * need to update our regions.
+   * @param aVisibleRect the area of the item that's visible
+   * @param aSolidColor if non-null, the visible area of the item is
+   * a constant color given by *aSolidColor
+   */
+  void Accumulate(ContainerState* aState,
+                  nsDisplayItem* aItem,
+                  const nsIntRegion& aClippedOpaqueRegion,
+                  const nsIntRect& aVisibleRect,
+                  const DisplayItemClip& aClip,
+                  LayerState aLayerState);
+  AnimatedGeometryRoot* GetAnimatedGeometryRoot() { return mAnimatedGeometryRoot; }
+
+  /**
+   * A region including the horizontal pan, vertical pan, and no action regions.
+   */
+  nsRegion CombinedTouchActionRegion();
+
+  /**
+   * Add the given hit regions to the hit regions to the hit retions for this
+   * PaintedLayer.
+   */
+  void AccumulateEventRegions(ContainerState* aState, nsDisplayLayerEventRegions* aEventRegions);
+
+  /**
+   * If this represents only a nsDisplayImage, and the image type supports being
+   * optimized to an ImageLayer, returns true.
+   */
+  bool CanOptimizeToImageLayer(nsDisplayListBuilder* aBuilder);
+
+  /**
+   * If this represents only a nsDisplayImage, and the image type supports being
+   * optimized to an ImageLayer, returns an ImageContainer for the underlying
+   * image if one is available.
+   */
+  already_AddRefed<ImageContainer> GetContainerForImageLayer(nsDisplayListBuilder* aBuilder);
+
+  bool VisibleAboveRegionIntersects(const nsIntRegion& aRegion) const
+  { return !mVisibleAboveRegion.Intersect(aRegion).IsEmpty(); }
+  bool VisibleRegionIntersects(const nsIntRegion& aRegion) const
+  { return !mVisibleRegion.Intersect(aRegion).IsEmpty(); }
+
+  /**
+   * The region of visible content in the layer, relative to the
+   * container layer (which is at the snapped top-left of the display
+   * list reference frame).
+   */
+  nsIntRegion  mVisibleRegion;
+  /**
+   * The region of visible content in the layer that is opaque.
+   * Same coordinate system as mVisibleRegion.
+   */
+  nsIntRegion  mOpaqueRegion;
+  /**
+   * The definitely-hit region for this PaintedLayer.
+   */
+  nsRegion  mHitRegion;
+  /**
+   * The maybe-hit region for this PaintedLayer.
+   */
+  nsRegion  mMaybeHitRegion;
+  /**
+   * The dispatch-to-content hit region for this PaintedLayer.
+   */
+  nsRegion  mDispatchToContentHitRegion;
+  /**
+   * The region for this PaintedLayer that is sensitive to events
+   * but disallows panning and zooming. This is an approximation
+   * and any deviation from the true region will be part of the
+   * mDispatchToContentHitRegion.
+   */
+  nsRegion mNoActionRegion;
+  /**
+   * The region for this PaintedLayer that is sensitive to events and
+   * allows horizontal panning but not zooming. This is an approximation
+   * and any deviation from the true region will be part of the
+   * mDispatchToContentHitRegion.
+   */
+  nsRegion mHorizontalPanRegion;
+  /**
+   * The region for this PaintedLayer that is sensitive to events and
+   * allows vertical panning but not zooming. This is an approximation
+   * and any deviation from the true region will be part of the
+   * mDispatchToContentHitRegion.
+   */
+  nsRegion mVerticalPanRegion;
+  /**
+   * Scaled versions of the bounds of mHitRegion and mMaybeHitRegion.
+   * We store these because FindPaintedLayerFor() needs to consume them
+   * in this form, and it's a hot code path so we don't want to scale
+   * them inside that function.
+   */
+  nsIntRect mScaledHitRegionBounds;
+  nsIntRect mScaledMaybeHitRegionBounds;
+  /**
+   * The "active scrolled root" for all content in the layer. Must
+   * be non-null; all content in a PaintedLayer must have the same
+   * active scrolled root.
+   */
+  AnimatedGeometryRoot* mAnimatedGeometryRoot;
+  /**
+   * The scroll clip for this layer.
+   */
+  const DisplayItemScrollClip* mScrollClip;
+  /**
+   * The offset between mAnimatedGeometryRoot and the reference frame.
+   */
+  nsPoint mAnimatedGeometryRootOffset;
+  /**
+   * If non-null, the frame from which we'll extract "fixed positioning"
+   * metadata for this layer. This can be a position:fixed frame or a viewport
+   * frame; the latter case is used for background-attachment:fixed content.
+   */
+  const nsIFrame* mReferenceFrame;
+  PaintedLayer* mLayer;
+  /**
+   * If mIsSolidColorInVisibleRegion is true, this is the color of the visible
+   * region.
+   */
+  nscolor      mSolidColor;
+  /**
+   * True if every pixel in mVisibleRegion will have color mSolidColor.
+   */
+  bool mIsSolidColorInVisibleRegion;
+  /**
+   * The target background color for smoothing fonts that are drawn on top of
+   * transparent parts of the layer.
+   */
+  nscolor mFontSmoothingBackgroundColor;
+  /**
+   * True if the layer contains exactly one item that returned true for
+   * ShouldFixToViewport.
+   */
+  bool mSingleItemFixedToViewport;
+  /**
+   * True if there is any text visible in the layer that's over
+   * transparent pixels in the layer.
+   */
+  bool mNeedComponentAlpha;
+  /**
+   * Set if the layer should be treated as transparent, even if its entire
+   * area is covered by opaque display items. For example, this needs to
+   * be set if something is going to "punch holes" in the layer by clearing
+   * part of its surface.
+   */
+  bool mForceTransparentSurface;
+  /**
+   * Set if all layers below this PaintedLayer should be hidden.
+   */
+  bool mHideAllLayersBelow;
+  /**
+   * Set if the opaque region for this layer can be applied to the parent
+   * animated geometry root of this layer's animated geometry root.
+   * We set this when a PaintedLayer's animated geometry root is a scrollframe
+   * and the PaintedLayer completely fills the displayport of the scrollframe.
+   */
+  bool mOpaqueForAnimatedGeometryRootParent;
+  /**
+   * Set if there is content in the layer that must avoid being flattened.
+   */
+  bool mDisableFlattening;
+  /**
+   * Set if the backface of this region is hidden to the user.
+   * Content that backface is hidden should not be draw on the layer
+   * with visible backface.
+   */
+  bool mBackfaceHidden;
+  /**
+   * Stores the pointer to the nsDisplayImage if we want to
+   * convert this to an ImageLayer.
+   */
+  nsDisplayImageContainer* mImage;
+  /**
+   * Stores the clip that we need to apply to the image or, if there is no
+   * image, a clip for SOME item in the layer. There is no guarantee which
+   * item's clip will be stored here and mItemClip should not be used to clip
+   * the whole layer - only some part of the clip should be used, as determined
+   * by PaintedDisplayItemLayerUserData::GetCommonClipCount() - which may even be
+   * no part at all.
+   */
+  DisplayItemClip mItemClip;
+  /**
+   * The first mCommonClipCount rounded rectangle clips are identical for
+   * all items in the layer.
+   * -1 if there are no items in the layer; must be >=0 by the time that this
+   * data is popped from the stack.
+   */
+  int32_t mCommonClipCount;
+  /**
+   * Index of this layer in mNewChildLayers.
+   */
+  int32_t mNewChildLayersIndex;
+  /*
+   * Updates mCommonClipCount by checking for rounded rect clips in common
+   * between the clip on a new item (aCurrentClip) and the common clips
+   * on items already in the layer (the first mCommonClipCount rounded rects
+   * in mItemClip).
+   */
+  void UpdateCommonClipCount(const DisplayItemClip& aCurrentClip);
+  /**
+   * The union of all the bounds of the display items in this layer.
+   */
+  nsIntRect mBounds;
+  /**
+   * The region of visible content above the layer and below the
+   * next PaintedLayerData currently in the stack, if any.
+   * This is a conservative approximation: it contains the true region.
+   */
+  nsIntRegion mVisibleAboveRegion;
+  /**
+   * All the display items that have been assigned to this painted layer.
+   * These items get added by Accumulate().
+   */
+  nsTArray<AssignedDisplayItem> mAssignedDisplayItems;
+
+};
+
+struct NewLayerEntry {
+  NewLayerEntry()
+    : mAnimatedGeometryRoot(nullptr)
+    , mScrollClip(nullptr)
+    , mLayerContentsVisibleRect(0, 0, -1, -1)
+    , mLayerState(LAYER_INACTIVE)
+    , mHideAllLayersBelow(false)
+    , mOpaqueForAnimatedGeometryRootParent(false)
+    , mPropagateComponentAlphaFlattening(true)
+    , mUntransformedVisibleRegion(false)
+  {}
+  // mLayer is null if the previous entry is for a PaintedLayer that hasn't
+  // been optimized to some other form (yet).
+  RefPtr<Layer> mLayer;
+  AnimatedGeometryRoot* mAnimatedGeometryRoot;
+  const DisplayItemScrollClip* mScrollClip;
+  // If non-null, this ScrollMetadata is set to the be the first ScrollMetadata
+  // on the layer.
+  UniquePtr<ScrollMetadata> mBaseScrollMetadata;
+  // The following are only used for retained layers (for occlusion
+  // culling of those layers). These regions are all relative to the
+  // container reference frame.
+  nsIntRegion mVisibleRegion;
+  nsIntRegion mOpaqueRegion;
+  // This rect is in the layer's own coordinate space. The computed visible
+  // region for the layer cannot extend beyond this rect.
+  nsIntRect mLayerContentsVisibleRect;
+  LayerState mLayerState;
+  bool mHideAllLayersBelow;
+  // When mOpaqueForAnimatedGeometryRootParent is true, the opaque region of
+  // this layer is opaque in the same position even subject to the animation of
+  // geometry of mAnimatedGeometryRoot. For example when mAnimatedGeometryRoot
+  // is a scrolled frame and the scrolled content is opaque everywhere in the
+  // displayport, we can set this flag.
+  // When this flag is set, we can treat this opaque region as covering
+  // content whose animated geometry root is the animated geometry root for
+  // mAnimatedGeometryRoot->GetParent().
+  bool mOpaqueForAnimatedGeometryRootParent;
+
+  // If true, then the content flags for this layer should contribute
+  // to our decision to flatten component alpha layers, false otherwise.
+  bool mPropagateComponentAlphaFlattening;
+  // mVisibleRegion is relative to the associated frame before
+  // transform.
+  bool mUntransformedVisibleRegion;
+};
+
+class PaintedLayerDataTree;
+
+/**
+ * This is tree node type for PaintedLayerDataTree.
+ * Each node corresponds to a different animated geometry root, and contains
+ * a stack of PaintedLayerDatas, in bottom-to-top order.
+ * There is at most one node per animated geometry root. The ancestor and
+ * descendant relations in PaintedLayerDataTree tree mirror those in the frame
+ * tree.
+ * Each node can have clip that describes the potential extents that items in
+ * this node can cover. If mHasClip is false, it means that the node's contents
+ * can move anywhere.
+ * Testing against the clip instead of the node's actual contents has the
+ * advantage that the node's contents can move or animate without affecting
+ * content in other nodes. So we don't need to re-layerize during animations
+ * (sync or async), and during async animations everything is guaranteed to
+ * look correct.
+ * The contents of a node's PaintedLayerData stack all share the node's
+ * animated geometry root. The child nodes are on top of the PaintedLayerData
+ * stack, in z-order, and the clip rects of the child nodes are allowed to
+ * intersect with the visible region or visible above region of their parent
+ * node's PaintedLayerDatas.
+ */
+class PaintedLayerDataNode {
+public:
+  PaintedLayerDataNode(PaintedLayerDataTree& aTree,
+                       PaintedLayerDataNode* aParent,
+                       AnimatedGeometryRoot* aAnimatedGeometryRoot);
+  ~PaintedLayerDataNode();
+
+  AnimatedGeometryRoot* GetAnimatedGeometryRoot() const { return mAnimatedGeometryRoot; }
+
+  /**
+   * Whether this node's contents can potentially intersect aRect.
+   * aRect is in our tree's ContainerState's coordinate space.
+   */
+  bool Intersects(const nsIntRect& aRect) const
+    { return !mHasClip || mClipRect.Intersects(aRect); }
+
+  /**
+   * Create a PaintedLayerDataNode for aAnimatedGeometryRoot, add it to our
+   * children, and return it.
+   */
+  PaintedLayerDataNode* AddChildNodeFor(AnimatedGeometryRoot* aAnimatedGeometryRoot);
+
+  /**
+   * Find a PaintedLayerData in our mPaintedLayerDataStack that aItem can be
+   * added to. Creates a new PaintedLayerData by calling
+   * aNewPaintedLayerCallback if necessary.
+   */
+  template<typename NewPaintedLayerCallbackType>
+  PaintedLayerData* FindPaintedLayerFor(const nsIntRect& aVisibleRect,
+                                        bool aBackfaceHidden,
+                                        const DisplayItemScrollClip* aScrollClip,
+                                        NewPaintedLayerCallbackType aNewPaintedLayerCallback);
+
+  /**
+   * Find an opaque background color for aRegion. Pulls a color from the parent
+   * geometry root if appropriate, but only if that color is present underneath
+   * the whole clip of this node, so that this node's contents can animate or
+   * move (possibly async) without having to change the background color.
+   * @param aUnderIndex Searching will start in mPaintedLayerDataStack right
+   *                    below aUnderIndex.
+   */
+  enum { ABOVE_TOP = -1 };
+  nscolor FindOpaqueBackgroundColor(const nsIntRegion& aRegion,
+                                    int32_t aUnderIndex = ABOVE_TOP) const;
+  /**
+   * Same as FindOpaqueBackgroundColor, but only returns a color if absolutely
+   * nothing is in between, so that it can be used for a layer that can move
+   * anywhere inside our clip.
+   */
+  nscolor FindOpaqueBackgroundColorCoveringEverything() const;
+
+  /**
+   * Adds aRect to this node's top PaintedLayerData's mVisibleAboveRegion,
+   * or mVisibleAboveBackgroundRegion if mPaintedLayerDataStack is empty.
+   */
+  void AddToVisibleAboveRegion(const nsIntRect& aRect);
+  /**
+   * Call this if all of our existing content can potentially be covered, so
+   * nothing can merge with it and all new content needs to create new items
+   * on top. This will finish all of our children and pop our whole
+   * mPaintedLayerDataStack.
+   */
+  void SetAllDrawingAbove();
+
+  /**
+   * Finish this node: Finish all children, finish our PaintedLayer contents,
+   * and (if requested) adjust our parent's visible above region to include
+   * our clip.
+   */
+  void Finish(bool aParentNeedsAccurateVisibleAboveRegion);
+
+  /**
+   * Finish any children that intersect aRect.
+   */
+  void FinishChildrenIntersecting(const nsIntRect& aRect);
+
+  /**
+   * Finish all children.
+   */
+  void FinishAllChildren() { FinishAllChildren(true); }
+
+protected:
+  /**
+   * Finish the topmost item in mPaintedLayerDataStack and pop it from the
+   * stack.
+   */
+  void PopPaintedLayerData();
+  /**
+   * Finish all items in mPaintedLayerDataStack and clear the stack.
+   */
+  void PopAllPaintedLayerData();
+  /**
+   * Finish all of our child nodes, but don't touch mPaintedLayerDataStack.
+   */
+  void FinishAllChildren(bool aThisNodeNeedsAccurateVisibleAboveRegion);
+  /**
+   * Pass off opaque background color searching to our parent node, if we have
+   * one.
+   */
+  nscolor FindOpaqueBackgroundColorInParentNode() const;
+
+  PaintedLayerDataTree& mTree;
+  PaintedLayerDataNode* mParent;
+  AnimatedGeometryRoot* mAnimatedGeometryRoot;
+
+  /**
+   * Our contents: a PaintedLayerData stack and our child nodes.
+   */
+  nsTArray<PaintedLayerData> mPaintedLayerDataStack;
+
+  /**
+   * UniquePtr is used here in the sense of "unique ownership", i.e. there is
+   * only one owner. Not in the sense of "this is the only pointer to the
+   * node": There are two other, non-owning, pointers to our child nodes: The
+   * node's respective children point to their parent node with their mParent
+   * pointer, and the tree keeps a map of animated geometry root to node in its
+   * mNodes member. These outside pointers are the reason that mChildren isn't
+   * just an nsTArray<PaintedLayerDataNode> (since the pointers would become
+   * invalid whenever the array expands its capacity).
+   */
+  nsTArray<UniquePtr<PaintedLayerDataNode>> mChildren;
+
+  /**
+   * The region that's covered between our "background" and the bottom of
+   * mPaintedLayerDataStack. This is used to indicate whether we can pull
+   * a background color from our parent node. If mVisibleAboveBackgroundRegion
+   * should be considered infinite, mAllDrawingAboveBackground will be true and
+   * the value of mVisibleAboveBackgroundRegion will be meaningless.
+   */
+  nsIntRegion mVisibleAboveBackgroundRegion;
+
+  /**
+   * Our clip, if we have any. If not, that means we can move anywhere, and
+   * mHasClip will be false and mClipRect will be meaningless.
+   */
+  nsIntRect mClipRect;
+  bool mHasClip;
+
+  /**
+   * Whether mVisibleAboveBackgroundRegion should be considered infinite.
+   */
+  bool mAllDrawingAboveBackground;
+};
+
+class ContainerState;
+
+/**
+ * A tree of PaintedLayerDataNodes. At any point in time, the tree only
+ * contains nodes for animated geometry roots that new items can potentially
+ * merge into. Any time content is added on top that overlaps existing things
+ * in such a way that we no longer want to merge new items with some existing
+ * content, that existing content gets "finished".
+ * The public-facing methods of this class are FindPaintedLayerFor,
+ * AddingOwnLayer, and Finish. The other public methods are for
+ * PaintedLayerDataNode.
+ * The tree calls out to its containing ContainerState for some things.
+ * All coordinates / rects in the tree or the tree nodes are in the
+ * ContainerState's coordinate space, i.e. relative to the reference frame and
+ * in layer pixels.
+ * The clip rects of sibling nodes never overlap. This is ensured by finishing
+ * existing nodes before adding new ones, if this property were to be violated.
+ * The root tree node doesn't get finished until the ContainerState is
+ * finished.
+ * The tree's root node is always the root reference frame of the builder. We
+ * don't stop at the container state's mContainerAnimatedGeometryRoot because
+ * some of our contents can have animated geometry roots that are not
+ * descendants of the container's animated geometry root. Every animated
+ * geometry root we encounter for our contents needs to have a defined place in
+ * the tree.
+ */
+class PaintedLayerDataTree {
+public:
+  PaintedLayerDataTree(ContainerState& aContainerState,
+                       nscolor& aBackgroundColor)
+    : mContainerState(aContainerState)
+    , mContainerUniformBackgroundColor(aBackgroundColor)
+  {}
+
+  ~PaintedLayerDataTree()
+  {
+    MOZ_ASSERT(!mRoot);
+    MOZ_ASSERT(mNodes.Count() == 0);
+  }
+
+  /**
+   * Notify our contents that some non-PaintedLayer content has been added.
+   * *aRect needs to be a rectangle that doesn't move with respect to
+   * aAnimatedGeometryRoot and that contains the added item.
+   * If aRect is null, the extents will be considered infinite.
+   * If aOutUniformBackgroundColor is non-null, it will be set to an opaque
+   * color that can be pulled into the background of the added content, or
+   * transparent if that is not possible.
+   */
+  void AddingOwnLayer(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                      const nsIntRect* aRect,
+                      nscolor* aOutUniformBackgroundColor);
+
+  /**
+   * Find a PaintedLayerData for aItem. This can either be an existing
+   * PaintedLayerData from inside a node in our tree, or a new one that gets
+   * created by a call out to aNewPaintedLayerCallback.
+   */
+  template<typename NewPaintedLayerCallbackType>
+  PaintedLayerData* FindPaintedLayerFor(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                        const DisplayItemScrollClip* aScrollClip,
+                                        const nsIntRect& aVisibleRect,
+                                        bool aBackfaceidden,
+                                        NewPaintedLayerCallbackType aNewPaintedLayerCallback);
+
+  /**
+   * Finish everything.
+   */
+  void Finish();
+
+  /**
+   * Get the parent animated geometry root of aAnimatedGeometryRoot.
+   * That's either aAnimatedGeometryRoot's animated geometry root, or, if
+   * that's aAnimatedGeometryRoot itself, then it's the animated geometry
+   * root for aAnimatedGeometryRoot's cross-doc parent frame.
+   */
+  AnimatedGeometryRoot* GetParentAnimatedGeometryRoot(AnimatedGeometryRoot* aAnimatedGeometryRoot);
+
+  /**
+   * Whether aAnimatedGeometryRoot has an intrinsic clip that doesn't move with
+   * respect to aAnimatedGeometryRoot's parent animated geometry root.
+   * If aAnimatedGeometryRoot is a scroll frame, this will be the scroll frame's
+   * scroll port, otherwise there is no clip.
+   * This method doesn't have much to do with PaintedLayerDataTree, but this is
+   * where we have easy access to a display list builder, which we use to get
+   * the clip rect result into the right coordinate space.
+   */
+  bool IsClippedWithRespectToParentAnimatedGeometryRoot(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                                        nsIntRect* aOutClip);
+
+  /**
+   * Called by PaintedLayerDataNode when it is finished, so that we can drop
+   * our pointers to it.
+   */
+  void NodeWasFinished(AnimatedGeometryRoot* aAnimatedGeometryRoot);
+
+  nsDisplayListBuilder* Builder() const;
+  ContainerState& ContState() const { return mContainerState; }
+  nscolor UniformBackgroundColor() const { return mContainerUniformBackgroundColor; }
+
+protected:
+  /**
+   * Finish all nodes that potentially intersect *aRect, where *aRect is a rect
+   * that doesn't move with respect to aAnimatedGeometryRoot.
+   * If aRect is null, *aRect will be considered infinite.
+   */
+  void FinishPotentiallyIntersectingNodes(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                          const nsIntRect* aRect);
+
+  /**
+   * Make sure that there is a node for aAnimatedGeometryRoot and all of its
+   * ancestor geometry roots. Return the node for aAnimatedGeometryRoot.
+   */
+  PaintedLayerDataNode* EnsureNodeFor(AnimatedGeometryRoot* aAnimatedGeometryRoot);
+
+  /**
+   * Find an existing node in the tree for an ancestor of aAnimatedGeometryRoot.
+   * *aOutAncestorChild will be set to the last ancestor that was encountered
+   * in the search up from aAnimatedGeometryRoot; it will be a child animated
+   * geometry root of the result, if neither are null.
+   */
+  PaintedLayerDataNode*
+    FindNodeForAncestorAnimatedGeometryRoot(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                            AnimatedGeometryRoot** aOutAncestorChild);
+
+  ContainerState& mContainerState;
+  UniquePtr<PaintedLayerDataNode> mRoot;
+
+  /**
+   * The uniform opaque color from behind this container layer, or
+   * NS_RGBA(0,0,0,0) if the background behind this container layer is not
+   * uniform and opaque. This color can be pulled into PaintedLayers that are
+   * directly above the background.
+   */
+  nscolor mContainerUniformBackgroundColor;
+
+  /**
+   * A hash map for quick access the node belonging to a particular animated
+   * geometry root.
+   */
+  nsDataHashtable<nsPtrHashKey<AnimatedGeometryRoot>, PaintedLayerDataNode*> mNodes;
+};
+
+/**
+ * This is a helper object used to build up the layer children for
+ * a ContainerLayer.
+ */
+class ContainerState {
+public:
+  ContainerState(nsDisplayListBuilder* aBuilder,
+                 LayerManager* aManager,
+                 FrameLayerBuilder* aLayerBuilder,
+                 nsIFrame* aContainerFrame,
+                 nsDisplayItem* aContainerItem,
+                 const nsRect& aContainerBounds,
+                 ContainerLayer* aContainerLayer,
+                 const ContainerLayerParameters& aParameters,
+                 bool aFlattenToSingleLayer,
+                 nscolor aBackgroundColor,
+                 const DisplayItemScrollClip* aContainerScrollClip) :
+    mBuilder(aBuilder), mManager(aManager),
+    mLayerBuilder(aLayerBuilder),
+    mContainerFrame(aContainerFrame),
+    mContainerLayer(aContainerLayer),
+    mContainerBounds(aContainerBounds),
+    mContainerScrollClip(aContainerScrollClip),
+    mScrollClipForPerspectiveChild(aParameters.mScrollClipForPerspectiveChild),
+    mParameters(aParameters),
+    mPaintedLayerDataTree(*this, aBackgroundColor),
+    mFlattenToSingleLayer(aFlattenToSingleLayer)
+  {
+    nsPresContext* presContext = aContainerFrame->PresContext();
+    mAppUnitsPerDevPixel = presContext->AppUnitsPerDevPixel();
+    mContainerReferenceFrame =
+      const_cast<nsIFrame*>(aContainerItem ? aContainerItem->ReferenceFrameForChildren() :
+                                             mBuilder->FindReferenceFrameFor(mContainerFrame));
+    bool isAtRoot = !aContainerItem || (aContainerItem->Frame() == mBuilder->RootReferenceFrame());
+    MOZ_ASSERT_IF(isAtRoot, mContainerReferenceFrame == mBuilder->RootReferenceFrame());
+    mContainerAnimatedGeometryRoot = isAtRoot
+      ? aBuilder->GetRootAnimatedGeometryRoot()
+      : aContainerItem->GetAnimatedGeometryRoot();
+    MOZ_ASSERT(!mBuilder->IsPaintingToWindow() ||
+      nsLayoutUtils::IsAncestorFrameCrossDoc(mBuilder->RootReferenceFrame(),
+                                             *mContainerAnimatedGeometryRoot));
+    // When AllowResidualTranslation is false, display items will be drawn
+    // scaled with a translation by integer pixels, so we know how the snapping
+    // will work.
+    mSnappingEnabled = aManager->IsSnappingEffectiveTransforms() &&
+      !mParameters.AllowResidualTranslation();
+    CollectOldLayers();
+  }
+
+  /**
+   * This is the method that actually walks a display list and builds
+   * the child layers.
+   */
+  void ProcessDisplayItems(nsDisplayList* aList);
+  /**
+   * This finalizes all the open PaintedLayers by popping every element off
+   * mPaintedLayerDataStack, then sets the children of the container layer
+   * to be all the layers in mNewChildLayers in that order and removes any
+   * layers as children of the container that aren't in mNewChildLayers.
+   * @param aTextContentFlags if any child layer has CONTENT_COMPONENT_ALPHA,
+   * set *aTextContentFlags to CONTENT_COMPONENT_ALPHA
+   */
+  void Finish(uint32_t *aTextContentFlags,
+              const nsIntRect& aContainerPixelBounds,
+              nsDisplayList* aChildItems, bool* aHasComponentAlphaChildren);
+
+  nscoord GetAppUnitsPerDevPixel() { return mAppUnitsPerDevPixel; }
+
+  nsIntRect ScaleToNearestPixels(const nsRect& aRect) const
+  {
+    return aRect.ScaleToNearestPixels(mParameters.mXScale, mParameters.mYScale,
+                                      mAppUnitsPerDevPixel);
+  }
+  nsIntRegion ScaleRegionToNearestPixels(const nsRegion& aRegion) const
+  {
+    return aRegion.ScaleToNearestPixels(mParameters.mXScale, mParameters.mYScale,
+                                        mAppUnitsPerDevPixel);
+  }
+  nsIntRect ScaleToOutsidePixels(const nsRect& aRect, bool aSnap = false) const
+  {
+    if (aSnap && mSnappingEnabled) {
+      return ScaleToNearestPixels(aRect);
+    }
+    return aRect.ScaleToOutsidePixels(mParameters.mXScale, mParameters.mYScale,
+                                      mAppUnitsPerDevPixel);
+  }
+  nsIntRect ScaleToInsidePixels(const nsRect& aRect, bool aSnap = false) const
+  {
+    if (aSnap && mSnappingEnabled) {
+      return ScaleToNearestPixels(aRect);
+    }
+    return aRect.ScaleToInsidePixels(mParameters.mXScale, mParameters.mYScale,
+                                     mAppUnitsPerDevPixel);
+  }
+
+  nsIntRegion ScaleRegionToInsidePixels(const nsRegion& aRegion, bool aSnap = false) const
+  {
+    if (aSnap && mSnappingEnabled) {
+      return ScaleRegionToNearestPixels(aRegion);
+    }
+    return aRegion.ScaleToInsidePixels(mParameters.mXScale, mParameters.mYScale,
+                                        mAppUnitsPerDevPixel);
+  }
+
+  nsIntRegion ScaleRegionToOutsidePixels(const nsRegion& aRegion, bool aSnap = false) const
+  {
+    if (aSnap && mSnappingEnabled) {
+      return ScaleRegionToNearestPixels(aRegion);
+    }
+    return aRegion.ScaleToOutsidePixels(mParameters.mXScale, mParameters.mYScale,
+                                        mAppUnitsPerDevPixel);
+  }
+
+  nsIFrame* GetContainerFrame() const { return mContainerFrame; }
+  nsDisplayListBuilder* Builder() const { return mBuilder; }
+
+  /**
+   * Check if we are currently inside an inactive layer.
+   */
+  bool IsInInactiveLayer() const {
+    return mLayerBuilder->GetContainingPaintedLayerData();
+  }
+
+  /**
+   * Sets aOuterVisibleRegion as aLayer's visible region.
+   * @param aOuterVisibleRegion
+   *   is in the coordinate space of the container reference frame.
+   * @param aLayerContentsVisibleRect, if non-null, is in the layer's own
+   *   coordinate system.
+   * @param aOuterUntransformed is true if the given aOuterVisibleRegion
+   *   is already untransformed with the matrix of the layer.
+   */
+  void SetOuterVisibleRegionForLayer(Layer* aLayer,
+                                     const nsIntRegion& aOuterVisibleRegion,
+                                     const nsIntRect* aLayerContentsVisibleRect = nullptr,
+                                     bool aOuterUntransformed = false) const;
+
+  /**
+   * Try to determine whether the PaintedLayer aData has a single opaque color
+   * covering aRect. If successful, return that color, otherwise return
+   * NS_RGBA(0,0,0,0).
+   * If aRect turns out not to intersect any content in the layer,
+   * *aOutIntersectsLayer will be set to false.
+   */
+  nscolor FindOpaqueBackgroundColorInLayer(const PaintedLayerData* aData,
+                                           const nsIntRect& aRect,
+                                           bool* aOutIntersectsLayer) const;
+
+  /**
+   * Indicate that we are done adding items to the PaintedLayer represented by
+   * aData. Make sure that a real PaintedLayer exists for it, and set the final
+   * visible region and opaque-content.
+   */
+  template<typename FindOpaqueBackgroundColorCallbackType>
+  void FinishPaintedLayerData(PaintedLayerData& aData, FindOpaqueBackgroundColorCallbackType aFindOpaqueBackgroundColor);
+
+protected:
+  friend class PaintedLayerData;
+
+  LayerManager::PaintedLayerCreationHint
+    GetLayerCreationHint(AnimatedGeometryRoot* aAnimatedGeometryRoot);
+
+  /**
+   * Creates a new PaintedLayer and sets up the transform on the PaintedLayer
+   * to account for scrolling.
+   */
+  already_AddRefed<PaintedLayer> CreatePaintedLayer(PaintedLayerData* aData);
+
+  /**
+   * Find a PaintedLayer for recycling, recycle it and prepare it for use, or
+   * return null if no suitable layer was found.
+   */
+  already_AddRefed<PaintedLayer> AttemptToRecyclePaintedLayer(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                                              nsDisplayItem* aItem,
+                                                              const nsPoint& aTopLeft);
+  /**
+   * Recycle aLayer and do any necessary invalidation.
+   */
+  PaintedDisplayItemLayerUserData* RecyclePaintedLayer(PaintedLayer* aLayer,
+                                                       AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                                       bool& didResetScrollPositionForLayerPixelAlignment);
+
+  /**
+   * Perform the last step of CreatePaintedLayer / AttemptToRecyclePaintedLayer:
+   * Initialize aData, set up the layer's transform for scrolling, and
+   * invalidate the layer for layer pixel alignment changes if necessary.
+   */
+  void PreparePaintedLayerForUse(PaintedLayer* aLayer,
+                                 PaintedDisplayItemLayerUserData* aData,
+                                 AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                 const nsIFrame* aReferenceFrame,
+                                 const nsPoint& aTopLeft,
+                                 bool aDidResetScrollPositionForLayerPixelAlignment);
+
+  /**
+   * Attempt to prepare an ImageLayer based upon the provided PaintedLayerData.
+   * Returns nullptr on failure.
+   */
+  already_AddRefed<Layer> PrepareImageLayer(PaintedLayerData* aData);
+
+  /**
+   * Attempt to prepare a ColorLayer based upon the provided PaintedLayerData.
+   * Returns nullptr on failure.
+   */
+  already_AddRefed<Layer> PrepareColorLayer(PaintedLayerData* aData);
+
+  /**
+   * Grab the next recyclable ColorLayer, or create one if there are no
+   * more recyclable ColorLayers.
+   */
+  already_AddRefed<ColorLayer> CreateOrRecycleColorLayer(PaintedLayer* aPainted);
+  /**
+   * Grab the next recyclable ImageLayer, or create one if there are no
+   * more recyclable ImageLayers.
+   */
+  already_AddRefed<ImageLayer> CreateOrRecycleImageLayer(PaintedLayer* aPainted);
+  /**
+   * Grab a recyclable ImageLayer for use as a mask layer for aLayer (that is a
+   * mask layer which has been used for aLayer before), or create one if such
+   * a layer doesn't exist.
+   *
+   * Since mask layers can exist either on the layer directly, or as a side-
+   * attachment to FrameMetrics (for ancestor scrollframe clips), we key the
+   * recycle operation on both the originating layer and the mask layer's
+   * index in the layer, if any.
+   */
+  struct MaskLayerKey;
+  already_AddRefed<ImageLayer>
+  CreateOrRecycleMaskImageLayerFor(const MaskLayerKey& aKey,
+                                   mozilla::function<void(Layer* aLayer)> aSetUserData);
+  /**
+   * Grabs all PaintedLayers and ColorLayers from the ContainerLayer and makes them
+   * available for recycling.
+   */
+  void CollectOldLayers();
+  /**
+   * If aItem used to belong to a PaintedLayer, invalidates the area of
+   * aItem in that layer. If aNewLayer is a PaintedLayer, invalidates the area of
+   * aItem in that layer.
+   */
+  void InvalidateForLayerChange(nsDisplayItem* aItem,
+                                PaintedLayer* aNewLayer);
+  /**
+   * Returns true if aItem's opaque area (in aOpaque) covers the entire
+   * scrollable area of its presshell.
+   */
+  bool ItemCoversScrollableArea(nsDisplayItem* aItem, const nsRegion& aOpaque);
+
+  /**
+   * Set FrameMetrics and scroll-induced clipping on aEntry's layer.
+   */
+  void SetupScrollingMetadata(NewLayerEntry* aEntry);
+
+  /**
+   * Applies occlusion culling.
+   * For each layer in mNewChildLayers, remove from its visible region the
+   * opaque regions of the layers at higher z-index, but only if they have
+   * the same animated geometry root and fixed-pos frame ancestor.
+   * The opaque region for the child layers that share the same animated
+   * geometry root as the container frame is returned in
+   * *aOpaqueRegionForContainer.
+   *
+   * Also sets scroll metadata on the layers.
+   */
+  void PostprocessRetainedLayers(nsIntRegion* aOpaqueRegionForContainer);
+
+  /**
+   * Computes the snapped opaque area of aItem. Sets aList's opaque flag
+   * if it covers the entire list bounds. Sets *aHideAllLayersBelow to true
+   * this item covers the entire viewport so that all layers below are
+   * permanently invisible.
+   */
+  nsIntRegion ComputeOpaqueRect(nsDisplayItem* aItem,
+                                AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                const DisplayItemClip& aClip,
+                                nsDisplayList* aList,
+                                bool* aHideAllLayersBelow,
+                                bool* aOpaqueForAnimatedGeometryRootParent);
+
+  /**
+   * Return a PaintedLayerData object that is initialized for a layer that
+   * aItem will be assigned to.
+   * @param  aItem                 The item that is going to be added.
+   * @param  aVisibleRect          The visible rect of the item.
+   * @param  aAnimatedGeometryRoot The item's animated geometry root.
+   * @param  aScrollClip           The scroll clip for this PaintedLayer.
+   * @param  aTopLeft              The offset between aAnimatedGeometryRoot and
+   *                               the reference frame.
+   * @param aShouldFixToViewport   If true, aAnimatedGeometryRoot is the
+   *                               viewport and we will be adding fixed-pos
+   *                               metadata for this layer because the display
+   *                               item returned true from ShouldFixToViewport.
+   */
+  PaintedLayerData NewPaintedLayerData(nsDisplayItem* aItem,
+                                       AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                       const DisplayItemScrollClip* aScrollClip,
+                                       const nsPoint& aTopLeft,
+                                       bool aShouldFixToViewport);
+
+  /* Build a mask layer to represent the clipping region. Will return null if
+   * there is no clipping specified or a mask layer cannot be built.
+   * Builds an ImageLayer for the appropriate backend; the mask is relative to
+   * aLayer's visible region.
+   * aLayer is the layer to be clipped.
+   * relative to the container reference frame
+   * aRoundedRectClipCount is used when building mask layers for PaintedLayers,
+   * SetupMaskLayer will build a mask layer for only the first
+   * aRoundedRectClipCount rounded rects in aClip
+   */
+  void SetupMaskLayer(Layer *aLayer, const DisplayItemClip& aClip,
+                      uint32_t aRoundedRectClipCount = UINT32_MAX);
+
+  /**
+   * If |aClip| has rounded corners, create a mask layer for them, and
+   * add it to |aLayer|'s ancestor mask layers, returning an index into
+   * the array of ancestor mask layers. Returns an empty Maybe if
+   * |aClip| does not have rounded corners, or if no mask layer could
+   * be created.
+   */
+  Maybe<size_t> SetupMaskLayerForScrolledClip(Layer* aLayer,
+                                              const DisplayItemClip& aClip);
+
+  /*
+   * Create/find a mask layer with suitable size for aMaskItem to paint
+   * css-positioned-masking onto.
+   */
+  void SetupMaskLayerForCSSMask(Layer* aLayer, nsDisplayMask* aMaskItem);
+
+  already_AddRefed<Layer> CreateMaskLayer(
+    Layer *aLayer, const DisplayItemClip& aClip,
+    const Maybe<size_t>& aForAncestorMaskLayer,
+    uint32_t aRoundedRectClipCount = UINT32_MAX);
+
+  bool ChooseAnimatedGeometryRoot(const nsDisplayList& aList,
+                                  AnimatedGeometryRoot **aAnimatedGeometryRoot);
+
+  nsDisplayListBuilder*            mBuilder;
+  LayerManager*                    mManager;
+  FrameLayerBuilder*               mLayerBuilder;
+  nsIFrame*                        mContainerFrame;
+  nsIFrame*                        mContainerReferenceFrame;
+  AnimatedGeometryRoot*            mContainerAnimatedGeometryRoot;
+  ContainerLayer*                  mContainerLayer;
+  nsRect                           mContainerBounds;
+  const DisplayItemScrollClip*     mContainerScrollClip;
+  const DisplayItemScrollClip*     mScrollClipForPerspectiveChild;
+#ifdef DEBUG
+  nsRect                           mAccumulatedChildBounds;
+#endif
+  ContainerLayerParameters         mParameters;
+  /**
+   * The region of PaintedLayers that should be invalidated every time
+   * we recycle one.
+   */
+  nsIntRegion                      mInvalidPaintedContent;
+  PaintedLayerDataTree             mPaintedLayerDataTree;
+  /**
+   * We collect the list of children in here. During ProcessDisplayItems,
+   * the layers in this array either have mContainerLayer as their parent,
+   * or no parent.
+   * PaintedLayers have two entries in this array: the second one is used only if
+   * the PaintedLayer is optimized away to a ColorLayer or ImageLayer.
+   * It's essential that this array is only appended to, since PaintedLayerData
+   * records the index of its PaintedLayer in this array.
+   */
+  typedef AutoTArray<NewLayerEntry,1> AutoLayersArray;
+  AutoLayersArray                  mNewChildLayers;
+  nsTHashtable<nsRefPtrHashKey<PaintedLayer>> mPaintedLayersAvailableForRecycling;
+  nscoord                          mAppUnitsPerDevPixel;
+  bool                             mSnappingEnabled;
+  bool                             mFlattenToSingleLayer;
+
+  struct MaskLayerKey {
+    MaskLayerKey() : mLayer(nullptr) {}
+    MaskLayerKey(Layer* aLayer, const Maybe<size_t>& aAncestorIndex)
+      : mLayer(aLayer),
+        mAncestorIndex(aAncestorIndex)
+    {}
+
+    PLDHashNumber Hash() const {
+      // Hash the layer and add the layer index to the hash.
+      return (NS_PTR_TO_UINT32(mLayer) >> 2)
+             + (mAncestorIndex ? (*mAncestorIndex + 1) : 0);
+    }
+    bool operator ==(const MaskLayerKey& aOther) const {
+      return mLayer == aOther.mLayer &&
+             mAncestorIndex == aOther.mAncestorIndex;
+    }
+
+    Layer* mLayer;
+    Maybe<size_t> mAncestorIndex;
+  };
+
+  nsDataHashtable<nsGenericHashKey<MaskLayerKey>, RefPtr<ImageLayer>>
+    mRecycledMaskImageLayers;
+};
+
+class PaintedDisplayItemLayerUserData : public LayerUserData
+{
+public:
+  PaintedDisplayItemLayerUserData() :
+    mMaskClipCount(0),
+    mForcedBackgroundColor(NS_RGBA(0,0,0,0)),
+    mFontSmoothingBackgroundColor(NS_RGBA(0,0,0,0)),
+    mXScale(1.f), mYScale(1.f),
+    mAppUnitsPerDevPixel(0),
+    mTranslation(0, 0),
+    mAnimatedGeometryRootPosition(0, 0) {}
+
+  /**
+   * Record the number of clips in the PaintedLayer's mask layer.
+   * Should not be reset when the layer is recycled since it is used to track
+   * changes in the use of mask layers.
+   */
+  uint32_t mMaskClipCount;
+
+  /**
+   * A color that should be painted over the bounds of the layer's visible
+   * region before any other content is painted.
+   */
+  nscolor mForcedBackgroundColor;
+
+  /**
+   * The target background color for smoothing fonts that are drawn on top of
+   * transparent parts of the layer.
+   */
+  nscolor mFontSmoothingBackgroundColor;
+
+  /**
+   * The resolution scale used.
+   */
+  float mXScale, mYScale;
+
+  /**
+   * The appunits per dev pixel for the items in this layer.
+   */
+  nscoord mAppUnitsPerDevPixel;
+
+  /**
+   * The offset from the PaintedLayer's 0,0 to the
+   * reference frame. This isn't necessarily the same as the transform
+   * set on the PaintedLayer since we might also be applying an extra
+   * offset specified by the parent ContainerLayer/
+   */
+  nsIntPoint mTranslation;
+
+  /**
+   * We try to make 0,0 of the PaintedLayer be the top-left of the
+   * border-box of the "active scrolled root" frame (i.e. the nearest ancestor
+   * frame for the display items that is being actively scrolled). But
+   * we force the PaintedLayer transform to be an integer translation, and we may
+   * have a resolution scale, so we have to snap the PaintedLayer transform, so
+   * 0,0 may not be exactly the top-left of the active scrolled root. Here we
+   * store the coordinates in PaintedLayer space of the top-left of the
+   * active scrolled root.
+   */
+  gfxPoint mAnimatedGeometryRootPosition;
+
+  nsIntRegion mRegionToInvalidate;
+
+  // The offset between the active scrolled root of this layer
+  // and the root of the container for the previous and current
+  // paints respectively.
+  nsPoint mLastAnimatedGeometryRootOrigin;
+  nsPoint mAnimatedGeometryRootOrigin;
+
+  RefPtr<ColorLayer> mColorLayer;
+  RefPtr<ImageLayer> mImageLayer;
+
+  // The region for which display item visibility for this layer has already
+  // been calculated. Used to reduce the number of calls to
+  // RecomputeVisibilityForItems if it is known in advance that a larger
+  // region will be painted during a transaction than in a single call to
+  // DrawPaintedLayer, for example when progressive paint is enabled.
+  nsIntRegion mVisibilityComputedRegion;
+};
+
+/*
+ * User data for layers which will be used as masks.
+ */
+struct MaskLayerUserData : public LayerUserData
+{
+  MaskLayerUserData()
+    : mScaleX(-1.0f)
+    , mScaleY(-1.0f)
+    , mAppUnitsPerDevPixel(-1)
+  { }
+  MaskLayerUserData(const DisplayItemClip& aClip,
+                    uint32_t aRoundedRectClipCount,
+                    int32_t aAppUnitsPerDevPixel,
+                    const ContainerLayerParameters& aParams)
+    : mScaleX(aParams.mXScale)
+    , mScaleY(aParams.mYScale)
+    , mOffset(aParams.mOffset)
+    , mAppUnitsPerDevPixel(aAppUnitsPerDevPixel)
+  {
+    aClip.AppendRoundedRects(&mRoundedClipRects, aRoundedRectClipCount);
+  }
+
+  void operator=(MaskLayerUserData&& aOther)
+  {
+    mScaleX = aOther.mScaleX;
+    mScaleY = aOther.mScaleY;
+    mOffset = aOther.mOffset;
+    mAppUnitsPerDevPixel = aOther.mAppUnitsPerDevPixel;
+    mRoundedClipRects.SwapElements(aOther.mRoundedClipRects);
+  }
+
+  bool
+  operator== (const MaskLayerUserData& aOther) const
+  {
+    return mRoundedClipRects == aOther.mRoundedClipRects &&
+           mScaleX == aOther.mScaleX &&
+           mScaleY == aOther.mScaleY &&
+           mOffset == aOther.mOffset &&
+           mAppUnitsPerDevPixel == aOther.mAppUnitsPerDevPixel;
+  }
+
+  // Keeps a MaskLayerImageKey alive by managing its mLayerCount member-var
+  MaskLayerImageCache::MaskLayerImageKeyRef mImageKey;
+  // properties of the mask layer; the mask layer may be re-used if these
+  // remain unchanged.
+  nsTArray<DisplayItemClip::RoundedRect> mRoundedClipRects;
+  // scale from the masked layer which is applied to the mask
+  float mScaleX, mScaleY;
+  // The ContainerLayerParameters offset which is applied to the mask's transform.
+  nsIntPoint mOffset;
+  int32_t mAppUnitsPerDevPixel;
+};
+
+/*
+ * User data for layers which will be used as masks for css positioned mask.
+ */
+struct CSSMaskLayerUserData : public LayerUserData
+{
+  CSSMaskLayerUserData()
+    : mImageLayers(nsStyleImageLayers::LayerType::Mask)
+  { }
+
+  CSSMaskLayerUserData(nsIFrame* aFrame, const nsIntRect& aBounds)
+    : mImageLayers(aFrame->StyleSVGReset()->mMask),
+      mContentRect(aFrame->GetContentRectRelativeToSelf()),
+      mPaddingRect(aFrame->GetPaddingRectRelativeToSelf()),
+      mBorderRect(aFrame->GetRectRelativeToSelf()),
+      mMarginRect(aFrame->GetMarginRectRelativeToSelf()),
+      mBounds(aBounds)
+  {
+    Hash(aFrame);
+  }
+
+  CSSMaskLayerUserData& operator=(const CSSMaskLayerUserData& aOther)
+  {
+    mImageLayers = aOther.mImageLayers;
+
+    mContentRect = aOther.mContentRect;
+    mPaddingRect = aOther.mPaddingRect;
+    mBorderRect = aOther.mBorderRect;
+    mMarginRect = aOther.mMarginRect;
+
+    mBounds = aOther.mBounds;
+
+    mHash = aOther.mHash;
+
+    return *this;
+  }
+
+  bool
+  operator==(const CSSMaskLayerUserData& aOther) const
+  {
+    if (mHash != aOther.mHash) {
+      return false;
+    }
+
+    if (mImageLayers.mLayers != aOther.mImageLayers.mLayers) {
+      return false;
+    }
+
+    if (!mContentRect.IsEqualEdges(aOther.mContentRect) ||
+        !mPaddingRect.IsEqualEdges(aOther.mPaddingRect) ||
+        !mBorderRect.IsEqualEdges(aOther.mBorderRect) ||
+        !mMarginRect.IsEqualEdges(aOther.mMarginRect)) {
+      return false;
+    }
+
+    if (!mBounds.IsEqualEdges(aOther.mBounds)) {
+      return false;
+    }
+
+    return true;
+  }
+
+private:
+  void Hash(nsIFrame* aFrame)
+  {
+    uint32_t hash = 0;
+
+    const nsStyleImageLayers& imageLayers = aFrame->StyleSVGReset()->mMask;
+    for (uint32_t i = 0; i < imageLayers.mLayers.Length(); i++) {
+      const nsStyleImageLayers::Layer& newLayer = imageLayers.mLayers[i];
+      hash = AddToHash(hash, HashBytes(&newLayer, sizeof(newLayer)));
+    }
+
+    hash = AddToHash(hash, HashBytes(&mContentRect, sizeof(mContentRect)));
+    hash = AddToHash(hash, HashBytes(&mPaddingRect, sizeof(mPaddingRect)));
+    hash = AddToHash(hash, HashBytes(&mBorderRect, sizeof(mBorderRect)));
+    hash = AddToHash(hash, HashBytes(&mMarginRect, sizeof(mMarginRect)));
+
+    hash = AddToHash(hash, HashBytes(&mBounds, sizeof(mBounds)));
+
+    mHash = hash;
+  }
+
+  nsStyleImageLayers mImageLayers;
+
+  nsRect mContentRect;
+  nsRect mPaddingRect;
+  nsRect mBorderRect;
+  nsRect mMarginRect;
+
+  nsIntRect mBounds;
+
+  uint32_t mHash;
+};
+
+/*
+ * A helper object to create a draw target for painting mask and create a
+ * image container to hold the drawing result. The caller can then bind this
+ * image container with a image mask layer via ImageLayer::SetContainer.
+ */
+class MaskImageData
+{
+public:
+  MaskImageData(const gfx::IntSize& aSize, LayerManager* aLayerManager)
+    : mTextureClientLocked(false)
+    , mSize(aSize)
+    , mLayerManager(aLayerManager)
+  {
+    MOZ_ASSERT(!mSize.IsEmpty());
+    MOZ_ASSERT(mLayerManager);
+  }
+
+  ~MaskImageData()
+  {
+    if (mTextureClientLocked) {
+      MOZ_ASSERT(mTextureClient);
+      // Clear DrawTarget before Unlock.
+      mDrawTarget = nullptr;
+      mTextureClient->Unlock();
+    }
+  }
+
+  gfx::DrawTarget* CreateDrawTarget()
+  {
+    if (mDrawTarget) {
+      return mDrawTarget;
+    }
+
+    if (mLayerManager->GetBackendType() == LayersBackend::LAYERS_BASIC) {
+      mDrawTarget = mLayerManager->CreateOptimalMaskDrawTarget(mSize);
+      return mDrawTarget;
+    }
+
+    MOZ_ASSERT(mLayerManager->GetBackendType() == LayersBackend::LAYERS_CLIENT);
+
+    ShadowLayerForwarder* fwd = mLayerManager->AsShadowForwarder();
+    if (!fwd) {
+      return nullptr;
+    }
+    mTextureClient =
+      TextureClient::CreateForDrawing(fwd,
+                                      SurfaceFormat::A8,
+                                      mSize,
+                                      BackendSelector::Content,
+                                      TextureFlags::DISALLOW_BIGIMAGE,
+                                      TextureAllocationFlags::ALLOC_CLEAR_BUFFER);
+    if (!mTextureClient) {
+      return nullptr;
+    }
+
+    mTextureClientLocked = mTextureClient->Lock(OpenMode::OPEN_READ_WRITE);
+    if (!mTextureClientLocked) {
+      return nullptr;
+    }
+
+    mDrawTarget = mTextureClient->BorrowDrawTarget();
+    return mDrawTarget;
+  }
+
+  already_AddRefed<ImageContainer> CreateImageAndImageContainer()
+  {
+    RefPtr<ImageContainer> container = mLayerManager->CreateImageContainer();
+    RefPtr<Image> image = CreateImage();
+
+    if (!image) {
+      return nullptr;
+    }
+    container->SetCurrentImageInTransaction(image);
+
+    return container.forget();
+  }
+
+private:
+  already_AddRefed<Image> CreateImage()
+  {
+    if (mLayerManager->GetBackendType() == LayersBackend::LAYERS_BASIC &&
+        mDrawTarget) {
+      RefPtr<SourceSurface> surface = mDrawTarget->Snapshot();
+      RefPtr<SourceSurfaceImage> image = new SourceSurfaceImage(mSize, surface);
+      // Disallow BIGIMAGE (splitting into multiple textures) for mask
+      // layer images
+      image->SetTextureFlags(TextureFlags::DISALLOW_BIGIMAGE);
+      return image.forget();
+    }
+
+    if (mLayerManager->GetBackendType() == LayersBackend::LAYERS_CLIENT &&
+        mTextureClient &&
+        mDrawTarget) {
+      RefPtr<TextureWrapperImage> image =
+          new TextureWrapperImage(mTextureClient, gfx::IntRect(gfx::IntPoint(0, 0), mSize));
+      return image.forget();
+    }
+
+    return nullptr;
+  }
+
+  bool mTextureClientLocked;
+  gfx::IntSize mSize;
+  LayerManager* mLayerManager;
+  RefPtr<gfx::DrawTarget> mDrawTarget;
+  RefPtr<TextureClient> mTextureClient;
+};
+
+/**
+  * Helper functions for getting user data and casting it to the correct type.
+  * aLayer is the layer where the user data is stored.
+  */
+MaskLayerUserData* GetMaskLayerUserData(Layer* aLayer)
+{
+  return static_cast<MaskLayerUserData*>(aLayer->GetUserData(&gMaskLayerUserData));
+}
+
+PaintedDisplayItemLayerUserData* GetPaintedDisplayItemLayerUserData(Layer* aLayer)
+{
+  return static_cast<PaintedDisplayItemLayerUserData*>(
+    aLayer->GetUserData(&gPaintedDisplayItemLayerUserData));
+}
+
+/* static */ void
+FrameLayerBuilder::Shutdown()
+{
+  if (gMaskLayerImageCache) {
+    delete gMaskLayerImageCache;
+    gMaskLayerImageCache = nullptr;
+  }
+}
+
+void
+FrameLayerBuilder::Init(nsDisplayListBuilder* aBuilder, LayerManager* aManager,
+                        PaintedLayerData* aLayerData)
+{
+  mDisplayListBuilder = aBuilder;
+  mRootPresContext = aBuilder->RootReferenceFrame()->PresContext()->GetRootPresContext();
+  if (mRootPresContext) {
+    mInitialDOMGeneration = mRootPresContext->GetDOMGeneration();
+  }
+  mContainingPaintedLayer = aLayerData;
+  aManager->SetUserData(&gLayerManagerLayerBuilder, this);
+}
+
+void
+FrameLayerBuilder::FlashPaint(gfxContext *aContext)
+{
+  float r = float(rand()) / RAND_MAX;
+  float g = float(rand()) / RAND_MAX;
+  float b = float(rand()) / RAND_MAX;
+  aContext->SetColor(Color(r, g, b, 0.4f));
+  aContext->Paint();
+}
+
+static FrameLayerBuilder::DisplayItemData*
+AssertDisplayItemData(FrameLayerBuilder::DisplayItemData* aData)
+{
+  MOZ_RELEASE_ASSERT(aData);
+  MOZ_RELEASE_ASSERT(sAliveDisplayItemDatas && sAliveDisplayItemDatas->Contains(aData));
+  MOZ_RELEASE_ASSERT(aData->mLayer);
+  return aData;
+}
+
+FrameLayerBuilder::DisplayItemData*
+FrameLayerBuilder::GetDisplayItemData(nsIFrame* aFrame, uint32_t aKey)
+{
+  const nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(LayerManagerDataProperty());
+  if (array) {
+    for (uint32_t i = 0; i < array->Length(); i++) {
+      DisplayItemData* item = AssertDisplayItemData(array->ElementAt(i));
+      if (item->mDisplayItemKey == aKey &&
+          item->mLayer->Manager() == mRetainingManager) {
+        return item;
+      }
+    }
+  }
+  return nullptr;
+}
+
+nsACString&
+AppendToString(nsACString& s, const nsIntRect& r,
+               const char* pfx="", const char* sfx="")
+{
+  s += pfx;
+  s += nsPrintfCString(
+    "(x=%d, y=%d, w=%d, h=%d)",
+    r.x, r.y, r.width, r.height);
+  return s += sfx;
+}
+
+nsACString&
+AppendToString(nsACString& s, const nsIntRegion& r,
+               const char* pfx="", const char* sfx="")
+{
+  s += pfx;
+
+  s += "< ";
+  for (auto iter = r.RectIter(); !iter.Done(); iter.Next()) {
+    AppendToString(s, iter.Get()) += "; ";
+  }
+  s += ">";
+
+  return s += sfx;
+}
+
+/**
+ * Invalidate aRegion in aLayer. aLayer is in the coordinate system
+ * *after* aTranslation has been applied, so we need to
+ * apply the inverse of that transform before calling InvalidateRegion.
+ */
+static void
+InvalidatePostTransformRegion(PaintedLayer* aLayer, const nsIntRegion& aRegion,
+                              const nsIntPoint& aTranslation)
+{
+  // Convert the region from the coordinates of the container layer
+  // (relative to the snapped top-left of the display list reference frame)
+  // to the PaintedLayer's own coordinates
+  nsIntRegion rgn = aRegion;
+  rgn.MoveBy(-aTranslation);
+  aLayer->InvalidateRegion(rgn);
+#ifdef MOZ_DUMP_PAINTING
+  if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+    nsAutoCString str;
+    AppendToString(str, rgn);
+    printf_stderr("Invalidating layer %p: %s\n", aLayer, str.get());
+  }
+#endif
+}
+
+static void
+InvalidatePostTransformRegion(PaintedLayer* aLayer, const nsRect& aRect,
+                              const DisplayItemClip& aClip,
+                              const nsIntPoint& aTranslation)
+{
+  PaintedDisplayItemLayerUserData* data =
+      static_cast<PaintedDisplayItemLayerUserData*>(aLayer->GetUserData(&gPaintedDisplayItemLayerUserData));
+
+  nsRect rect = aClip.ApplyNonRoundedIntersection(aRect);
+
+  nsIntRect pixelRect = rect.ScaleToOutsidePixels(data->mXScale, data->mYScale, data->mAppUnitsPerDevPixel);
+  InvalidatePostTransformRegion(aLayer, pixelRect, aTranslation);
+}
+
+
+static nsIntPoint
+GetTranslationForPaintedLayer(PaintedLayer* aLayer)
+{
+  PaintedDisplayItemLayerUserData* data =
+    static_cast<PaintedDisplayItemLayerUserData*>
+      (aLayer->GetUserData(&gPaintedDisplayItemLayerUserData));
+  NS_ASSERTION(data, "Must be a tracked painted layer!");
+
+  return data->mTranslation;
+}
+
+/**
+ * Some frames can have multiple, nested, retaining layer managers
+ * associated with them (normal manager, inactive managers, SVG effects).
+ * In these cases we store the 'outermost' LayerManager data property
+ * on the frame since we can walk down the chain from there.
+ *
+ * If one of these frames has just been destroyed, we will free the inner
+ * layer manager when removing the entry from mFramesWithLayers. Destroying
+ * the layer manager destroys the LayerManagerData and calls into
+ * the DisplayItemData destructor. If the inner layer manager had any
+ * items with the same frame, then we attempt to retrieve properties
+ * from the deleted frame.
+ *
+ * Cache the destroyed frame pointer here so we can avoid crashing in this case.
+ */
+
+/* static */ void
+FrameLayerBuilder::RemoveFrameFromLayerManager(const nsIFrame* aFrame,
+                                               nsTArray<DisplayItemData*>* aArray)
+{
+  MOZ_RELEASE_ASSERT(!sDestroyedFrame);
+  sDestroyedFrame = aFrame;
+
+  // Hold a reference to all the items so that they don't get
+  // deleted from under us.
+  nsTArray<RefPtr<DisplayItemData> > arrayCopy;
+  for (DisplayItemData* data : *aArray) {
+    arrayCopy.AppendElement(data);
+  }
+
+#ifdef DEBUG_DISPLAY_ITEM_DATA
+  if (aArray->Length()) {
+    LayerManagerData *rootData = aArray->ElementAt(0)->mParent;
+    while (rootData->mParent) {
+      rootData = rootData->mParent;
+    }
+    printf_stderr("Removing frame %p - dumping display data\n", aFrame);
+    rootData->Dump();
+  }
+#endif
+
+  for (DisplayItemData* data : *aArray) {
+    PaintedLayer* t = data->mLayer->AsPaintedLayer();
+    if (t) {
+      PaintedDisplayItemLayerUserData* paintedData =
+          static_cast<PaintedDisplayItemLayerUserData*>(t->GetUserData(&gPaintedDisplayItemLayerUserData));
+      if (paintedData) {
+        nsRegion old = data->mGeometry->ComputeInvalidationRegion();
+        nsIntRegion rgn = old.ScaleToOutsidePixels(paintedData->mXScale, paintedData->mYScale, paintedData->mAppUnitsPerDevPixel);
+        rgn.MoveBy(-GetTranslationForPaintedLayer(t));
+        paintedData->mRegionToInvalidate.Or(paintedData->mRegionToInvalidate, rgn);
+        paintedData->mRegionToInvalidate.SimplifyOutward(8);
+      }
+    }
+
+    data->mParent->mDisplayItems.RemoveEntry(data);
+  }
+
+  arrayCopy.Clear();
+  delete aArray;
+  sDestroyedFrame = nullptr;
+}
+
+void
+FrameLayerBuilder::DidBeginRetainedLayerTransaction(LayerManager* aManager)
+{
+  mRetainingManager = aManager;
+  LayerManagerData* data = static_cast<LayerManagerData*>
+    (aManager->GetUserData(&gLayerManagerUserData));
+  if (data) {
+    mInvalidateAllLayers = data->mInvalidateAllLayers;
+  } else {
+    data = new LayerManagerData(aManager);
+    aManager->SetUserData(&gLayerManagerUserData, data);
+  }
+}
+
+void
+FrameLayerBuilder::StoreOptimizedLayerForFrame(nsDisplayItem* aItem, Layer* aLayer)
+{
+  if (!mRetainingManager) {
+    return;
+  }
+
+  DisplayItemData* data = GetDisplayItemDataForManager(aItem, aLayer->Manager());
+  NS_ASSERTION(data, "Must have already stored data for this item!");
+  data->mOptLayer = aLayer;
+}
+
+void
+FrameLayerBuilder::DidEndTransaction()
+{
+  GetMaskLayerImageCache()->Sweep();
+}
+
+void
+FrameLayerBuilder::WillEndTransaction()
+{
+  if (!mRetainingManager) {
+    return;
+  }
+
+  // We need to save the data we'll need to support retaining.
+  LayerManagerData* data = static_cast<LayerManagerData*>
+    (mRetainingManager->GetUserData(&gLayerManagerUserData));
+  NS_ASSERTION(data, "Must have data!");
+
+  // Update all the frames that used to have layers.
+  for (auto iter = data->mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
+    DisplayItemData* data = iter.Get()->GetKey();
+    if (!data->mUsed) {
+      // This item was visible, but isn't anymore.
+      PaintedLayer* t = data->mLayer->AsPaintedLayer();
+      if (t && data->mGeometry) {
+#ifdef MOZ_DUMP_PAINTING
+        if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+          printf_stderr("Invalidating unused display item (%i) belonging to frame %p from layer %p\n", data->mDisplayItemKey, data->mFrameList[0], t);
+        }
+#endif
+        InvalidatePostTransformRegion(t,
+                                      data->mGeometry->ComputeInvalidationRegion(),
+                                      data->mClip,
+                                      GetLastPaintOffset(t));
+      }
+
+      data->ClearAnimationCompositorState();
+      iter.Remove();
+    } else {
+      ComputeGeometryChangeForItem(data);
+    }
+  }
+
+  data->mInvalidateAllLayers = false;
+}
+
+/* static */ FrameLayerBuilder::DisplayItemData*
+FrameLayerBuilder::GetDisplayItemDataForManager(nsDisplayItem* aItem,
+                                                LayerManager* aManager)
+{
+  const nsTArray<DisplayItemData*>* array =
+    aItem->Frame()->Properties().Get(LayerManagerDataProperty());
+  if (array) {
+    for (uint32_t i = 0; i < array->Length(); i++) {
+      DisplayItemData* item = AssertDisplayItemData(array->ElementAt(i));
+      if (item->mDisplayItemKey == aItem->GetPerFrameKey() &&
+          item->mLayer->Manager() == aManager) {
+        return item;
+      }
+    }
+  }
+  return nullptr;
+}
+
+bool
+FrameLayerBuilder::HasRetainedDataFor(nsIFrame* aFrame, uint32_t aDisplayItemKey)
+{
+  const nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(LayerManagerDataProperty());
+  if (array) {
+    for (uint32_t i = 0; i < array->Length(); i++) {
+      if (AssertDisplayItemData(array->ElementAt(i))->mDisplayItemKey == aDisplayItemKey) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+void
+FrameLayerBuilder::IterateRetainedDataFor(nsIFrame* aFrame, DisplayItemDataCallback aCallback)
+{
+  const nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(LayerManagerDataProperty());
+  if (!array) {
+    return;
+  }
+
+  for (uint32_t i = 0; i < array->Length(); i++) {
+    DisplayItemData* data = AssertDisplayItemData(array->ElementAt(i));
+    if (data->mDisplayItemKey != nsDisplayItem::TYPE_ZERO) {
+      aCallback(aFrame, data);
+    }
+  }
+}
+
+FrameLayerBuilder::DisplayItemData*
+FrameLayerBuilder::GetOldLayerForFrame(nsIFrame* aFrame, uint32_t aDisplayItemKey)
+{
+  // If we need to build a new layer tree, then just refuse to recycle
+  // anything.
+  if (!mRetainingManager || mInvalidateAllLayers)
+    return nullptr;
+
+  DisplayItemData *data = GetDisplayItemData(aFrame, aDisplayItemKey);
+
+  if (data && data->mLayer->Manager() == mRetainingManager) {
+    return data;
+  }
+  return nullptr;
+}
+
+Layer*
+FrameLayerBuilder::GetOldLayerFor(nsDisplayItem* aItem,
+                                  nsDisplayItemGeometry** aOldGeometry,
+                                  DisplayItemClip** aOldClip)
+{
+  uint32_t key = aItem->GetPerFrameKey();
+  nsIFrame* frame = aItem->Frame();
+
+  DisplayItemData* oldData = GetOldLayerForFrame(frame, key);
+  if (oldData) {
+    if (aOldGeometry) {
+      *aOldGeometry = oldData->mGeometry.get();
+    }
+    if (aOldClip) {
+      *aOldClip = &oldData->mClip;
+    }
+    return oldData->mLayer;
+  }
+
+  return nullptr;
+}
+
+void
+FrameLayerBuilder::ClearCachedGeometry(nsDisplayItem* aItem)
+{
+  uint32_t key = aItem->GetPerFrameKey();
+  nsIFrame* frame = aItem->Frame();
+
+  DisplayItemData* oldData = GetOldLayerForFrame(frame, key);
+  if (oldData) {
+    oldData->mGeometry = nullptr;
+  }
+}
+
+/* static */ Layer*
+FrameLayerBuilder::GetDebugOldLayerFor(nsIFrame* aFrame, uint32_t aDisplayItemKey)
+{
+  const nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(LayerManagerDataProperty());
+
+  if (!array) {
+    return nullptr;
+  }
+
+  for (uint32_t i = 0; i < array->Length(); i++) {
+    DisplayItemData *data = AssertDisplayItemData(array->ElementAt(i));
+
+    if (data->mDisplayItemKey == aDisplayItemKey) {
+      return data->mLayer;
+    }
+  }
+  return nullptr;
+}
+
+/* static */ PaintedLayer*
+FrameLayerBuilder::GetDebugSingleOldPaintedLayerForFrame(nsIFrame* aFrame)
+{
+  const nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(LayerManagerDataProperty());
+
+  if (!array) {
+    return nullptr;
+  }
+
+  Layer* layer = nullptr;
+  for (DisplayItemData* data : *array) {
+    AssertDisplayItemData(data);
+    if (!data->mLayer->AsPaintedLayer()) {
+      continue;
+    }
+    if (layer && layer != data->mLayer) {
+      // More than one layer assigned, bail.
+      return nullptr;
+    }
+    layer = data->mLayer;
+  }
+
+  if (!layer) {
+    return nullptr;
+  }
+
+  return layer->AsPaintedLayer();
+}
+
+// Reset state that should not persist when a layer is recycled.
+static void
+ResetLayerStateForRecycling(Layer* aLayer) {
+  // Currently, this clears the mask layer and ancestor mask layers.
+  // Other cleanup may be added here.
+  aLayer->SetMaskLayer(nullptr);
+  aLayer->SetAncestorMaskLayers({});
+}
+
+already_AddRefed<ColorLayer>
+ContainerState::CreateOrRecycleColorLayer(PaintedLayer *aPainted)
+{
+  PaintedDisplayItemLayerUserData* data =
+      static_cast<PaintedDisplayItemLayerUserData*>(aPainted->GetUserData(&gPaintedDisplayItemLayerUserData));
+  RefPtr<ColorLayer> layer = data->mColorLayer;
+  if (layer) {
+    ResetLayerStateForRecycling(layer);
+    layer->ClearExtraDumpInfo();
+  } else {
+    // Create a new layer
+    layer = mManager->CreateColorLayer();
+    if (!layer)
+      return nullptr;
+    // Mark this layer as being used for painting display items
+    data->mColorLayer = layer;
+    layer->SetUserData(&gColorLayerUserData, nullptr);
+
+    // Remove other layer types we might have stored for this PaintedLayer
+    data->mImageLayer = nullptr;
+  }
+  return layer.forget();
+}
+
+already_AddRefed<ImageLayer>
+ContainerState::CreateOrRecycleImageLayer(PaintedLayer *aPainted)
+{
+  PaintedDisplayItemLayerUserData* data =
+      static_cast<PaintedDisplayItemLayerUserData*>(aPainted->GetUserData(&gPaintedDisplayItemLayerUserData));
+  RefPtr<ImageLayer> layer = data->mImageLayer;
+  if (layer) {
+    ResetLayerStateForRecycling(layer);
+    layer->ClearExtraDumpInfo();
+  } else {
+    // Create a new layer
+    layer = mManager->CreateImageLayer();
+    if (!layer)
+      return nullptr;
+    // Mark this layer as being used for painting display items
+    data->mImageLayer = layer;
+    layer->SetUserData(&gImageLayerUserData, nullptr);
+
+    // Remove other layer types we might have stored for this PaintedLayer
+    data->mColorLayer = nullptr;
+  }
+  return layer.forget();
+}
+
+already_AddRefed<ImageLayer>
+ContainerState::CreateOrRecycleMaskImageLayerFor(const MaskLayerKey& aKey,
+                                                 mozilla::function<void(Layer* aLayer)> aSetUserData)
+{
+  RefPtr<ImageLayer> result = mRecycledMaskImageLayers.Get(aKey);
+  if (result) {
+    mRecycledMaskImageLayers.Remove(aKey);
+    aKey.mLayer->ClearExtraDumpInfo();
+    // XXX if we use clip on mask layers, null it out here
+  } else {
+    // Create a new layer
+    result = mManager->CreateImageLayer();
+    if (!result)
+      return nullptr;
+    aSetUserData(result);
+  }
+
+  return result.forget();
+}
+
+static const double SUBPIXEL_OFFSET_EPSILON = 0.02;
+
+/**
+ * This normally computes NSToIntRoundUp(aValue). However, if that would
+ * give a residual near 0.5 while aOldResidual is near -0.5, or
+ * it would give a residual near -0.5 while aOldResidual is near 0.5, then
+ * instead we return the integer in the other direction so that the residual
+ * is close to aOldResidual.
+ */
+static int32_t
+RoundToMatchResidual(double aValue, double aOldResidual)
+{
+  int32_t v = NSToIntRoundUp(aValue);
+  double residual = aValue - v;
+  if (aOldResidual < 0) {
+    if (residual > 0 && fabs(residual - 1.0 - aOldResidual) < SUBPIXEL_OFFSET_EPSILON) {
+      // Round up instead
+      return int32_t(ceil(aValue));
+    }
+  } else if (aOldResidual > 0) {
+    if (residual < 0 && fabs(residual + 1.0 - aOldResidual) < SUBPIXEL_OFFSET_EPSILON) {
+      // Round down instead
+      return int32_t(floor(aValue));
+    }
+  }
+  return v;
+}
+
+static void
+ResetScrollPositionForLayerPixelAlignment(AnimatedGeometryRoot* aAnimatedGeometryRoot)
+{
+  nsIScrollableFrame* sf = nsLayoutUtils::GetScrollableFrameFor(*aAnimatedGeometryRoot);
+  if (sf) {
+    sf->ResetScrollPositionForLayerPixelAlignment();
+  }
+}
+
+static void
+InvalidateEntirePaintedLayer(PaintedLayer* aLayer, AnimatedGeometryRoot* aAnimatedGeometryRoot, const char *aReason)
+{
+#ifdef MOZ_DUMP_PAINTING
+  if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+    printf_stderr("Invalidating entire layer %p: %s\n", aLayer, aReason);
+  }
+#endif
+  nsIntRect invalidate = aLayer->GetValidRegion().GetBounds();
+  aLayer->InvalidateRegion(invalidate);
+  aLayer->SetInvalidRectToVisibleRegion();
+  ResetScrollPositionForLayerPixelAlignment(aAnimatedGeometryRoot);
+}
+
+LayerManager::PaintedLayerCreationHint
+ContainerState::GetLayerCreationHint(AnimatedGeometryRoot* aAnimatedGeometryRoot)
+{
+  // Check whether the layer will be scrollable. This is used as a hint to
+  // influence whether tiled layers are used or not.
+
+  // Check creation hint inherited from our parent.
+  if (mParameters.mLayerCreationHint == LayerManager::SCROLLABLE) {
+    return LayerManager::SCROLLABLE;
+  }
+
+  // Check whether there's any active scroll frame on the animated geometry
+  // root chain.
+  for (AnimatedGeometryRoot* agr = aAnimatedGeometryRoot;
+       agr && agr != mContainerAnimatedGeometryRoot;
+       agr = agr->mParentAGR) {
+    nsIFrame* fParent = nsLayoutUtils::GetCrossDocParentFrame(*agr);
+    if (!fParent) {
+      break;
+    }
+    nsIScrollableFrame* scrollable = do_QueryFrame(fParent);
+    if (scrollable
+  #ifdef MOZ_B2G
+        && scrollable->WantAsyncScroll()
+  #endif
+       ) {
+      // WantAsyncScroll() returns false when the frame has overflow:hidden,
+      // so we won't create tiled layers for overflow:hidden frames even if
+      // they have a display port. The main purpose of the WantAsyncScroll check
+      // is to allow the B2G camera app to use hardware composer for compositing.
+      return LayerManager::SCROLLABLE;
+    }
+  }
+  return LayerManager::NONE;
+}
+
+already_AddRefed<PaintedLayer>
+ContainerState::AttemptToRecyclePaintedLayer(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                             nsDisplayItem* aItem,
+                                             const nsPoint& aTopLeft)
+{
+  Layer* oldLayer = mLayerBuilder->GetOldLayerFor(aItem);
+  if (!oldLayer || !oldLayer->AsPaintedLayer() ||
+      !mPaintedLayersAvailableForRecycling.Contains(oldLayer->AsPaintedLayer())) {
+    return nullptr;
+  }
+
+  // Try to recycle a layer
+  RefPtr<PaintedLayer> layer = oldLayer->AsPaintedLayer();
+  mPaintedLayersAvailableForRecycling.RemoveEntry(layer);
+
+  // Check if the layer hint has changed and whether or not the layer should
+  // be recreated because of it.
+  if (!layer->IsOptimizedFor(GetLayerCreationHint(aAnimatedGeometryRoot))) {
+    return nullptr;
+  }
+
+  bool didResetScrollPositionForLayerPixelAlignment = false;
+  PaintedDisplayItemLayerUserData* data =
+    RecyclePaintedLayer(layer, aAnimatedGeometryRoot,
+                        didResetScrollPositionForLayerPixelAlignment);
+  PreparePaintedLayerForUse(layer, data, aAnimatedGeometryRoot, aItem->ReferenceFrame(),
+                            aTopLeft,
+                            didResetScrollPositionForLayerPixelAlignment);
+
+  return layer.forget();
+}
+
+already_AddRefed<PaintedLayer>
+ContainerState::CreatePaintedLayer(PaintedLayerData* aData)
+{
+  LayerManager::PaintedLayerCreationHint creationHint =
+    GetLayerCreationHint(aData->mAnimatedGeometryRoot);
+
+  // Create a new painted layer
+  RefPtr<PaintedLayer> layer = mManager->CreatePaintedLayerWithHint(creationHint);
+  if (!layer) {
+    return nullptr;
+  }
+
+  // Mark this layer as being used for painting display items
+  PaintedDisplayItemLayerUserData* userData = new PaintedDisplayItemLayerUserData();
+  layer->SetUserData(&gPaintedDisplayItemLayerUserData, userData);
+  ResetScrollPositionForLayerPixelAlignment(aData->mAnimatedGeometryRoot);
+
+  PreparePaintedLayerForUse(layer, userData, aData->mAnimatedGeometryRoot,
+                            aData->mReferenceFrame,
+                            aData->mAnimatedGeometryRootOffset, true);
+
+  return layer.forget();
+}
+
+PaintedDisplayItemLayerUserData*
+ContainerState::RecyclePaintedLayer(PaintedLayer* aLayer,
+                                    AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                    bool& didResetScrollPositionForLayerPixelAlignment)
+{
+  // Clear clip rect and mask layer so we don't accidentally stay clipped.
+  // We will reapply any necessary clipping.
+  ResetLayerStateForRecycling(aLayer);
+  aLayer->ClearExtraDumpInfo();
+
+  PaintedDisplayItemLayerUserData* data =
+    static_cast<PaintedDisplayItemLayerUserData*>(
+      aLayer->GetUserData(&gPaintedDisplayItemLayerUserData));
+  NS_ASSERTION(data, "Recycled PaintedLayers must have user data");
+
+  // This gets called on recycled PaintedLayers that are going to be in the
+  // final layer tree, so it's a convenient time to invalidate the
+  // content that changed where we don't know what PaintedLayer it belonged
+  // to, or if we need to invalidate the entire layer, we can do that.
+  // This needs to be done before we update the PaintedLayer to its new
+  // transform. See nsGfxScrollFrame::InvalidateInternal, where
+  // we ensure that mInvalidPaintedContent is updated according to the
+  // scroll position as of the most recent paint.
+  if (!FuzzyEqual(data->mXScale, mParameters.mXScale, 0.00001f) ||
+      !FuzzyEqual(data->mYScale, mParameters.mYScale, 0.00001f) ||
+      data->mAppUnitsPerDevPixel != mAppUnitsPerDevPixel) {
+#ifdef MOZ_DUMP_PAINTING
+  if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+    printf_stderr("Recycled layer %p changed scale\n", aLayer);
+  }
+#endif
+    InvalidateEntirePaintedLayer(aLayer, aAnimatedGeometryRoot, "recycled layer changed state");
+    didResetScrollPositionForLayerPixelAlignment = true;
+  }
+  if (!data->mRegionToInvalidate.IsEmpty()) {
+#ifdef MOZ_DUMP_PAINTING
+    if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+      printf_stderr("Invalidating deleted frame content from layer %p\n", aLayer);
+    }
+#endif
+    aLayer->InvalidateRegion(data->mRegionToInvalidate);
+#ifdef MOZ_DUMP_PAINTING
+    if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+      nsAutoCString str;
+      AppendToString(str, data->mRegionToInvalidate);
+      printf_stderr("Invalidating layer %p: %s\n", aLayer, str.get());
+    }
+#endif
+    data->mRegionToInvalidate.SetEmpty();
+  }
+  return data;
+}
+
+void
+ContainerState::PreparePaintedLayerForUse(PaintedLayer* aLayer,
+                                          PaintedDisplayItemLayerUserData* aData,
+                                          AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                          const nsIFrame* aReferenceFrame,
+                                          const nsPoint& aTopLeft,
+                                          bool didResetScrollPositionForLayerPixelAlignment)
+{
+  aData->mXScale = mParameters.mXScale;
+  aData->mYScale = mParameters.mYScale;
+  aData->mLastAnimatedGeometryRootOrigin = aData->mAnimatedGeometryRootOrigin;
+  aData->mAnimatedGeometryRootOrigin = aTopLeft;
+  aData->mAppUnitsPerDevPixel = mAppUnitsPerDevPixel;
+  aLayer->SetAllowResidualTranslation(mParameters.AllowResidualTranslation());
+
+  mLayerBuilder->SavePreviousDataForLayer(aLayer, aData->mMaskClipCount);
+
+  // Set up transform so that 0,0 in the PaintedLayer corresponds to the
+  // (pixel-snapped) top-left of the aAnimatedGeometryRoot.
+  nsPoint offset = (*aAnimatedGeometryRoot)->GetOffsetToCrossDoc(aReferenceFrame);
+  nscoord appUnitsPerDevPixel = (*aAnimatedGeometryRoot)->PresContext()->AppUnitsPerDevPixel();
+  gfxPoint scaledOffset(
+      NSAppUnitsToDoublePixels(offset.x, appUnitsPerDevPixel)*mParameters.mXScale,
+      NSAppUnitsToDoublePixels(offset.y, appUnitsPerDevPixel)*mParameters.mYScale);
+  // We call RoundToMatchResidual here so that the residual after rounding
+  // is close to aData->mAnimatedGeometryRootPosition if possible.
+  nsIntPoint pixOffset(RoundToMatchResidual(scaledOffset.x, aData->mAnimatedGeometryRootPosition.x),
+                       RoundToMatchResidual(scaledOffset.y, aData->mAnimatedGeometryRootPosition.y));
+  aData->mTranslation = pixOffset;
+  pixOffset += mParameters.mOffset;
+  Matrix matrix = Matrix::Translation(pixOffset.x, pixOffset.y);
+  aLayer->SetBaseTransform(Matrix4x4::From2D(matrix));
+
+  aData->mVisibilityComputedRegion.SetEmpty();
+
+  // FIXME: Temporary workaround for bug 681192 and bug 724786.
+#ifndef MOZ_WIDGET_ANDROID
+  // Calculate exact position of the top-left of the active scrolled root.
+  // This might not be 0,0 due to the snapping in ScaleToNearestPixels.
+  gfxPoint animatedGeometryRootTopLeft = scaledOffset - ThebesPoint(matrix.GetTranslation()) + mParameters.mOffset;
+  // If it has changed, then we need to invalidate the entire layer since the
+  // pixels in the layer buffer have the content at a (subpixel) offset
+  // from what we need.
+  if (!animatedGeometryRootTopLeft.WithinEpsilonOf(aData->mAnimatedGeometryRootPosition, SUBPIXEL_OFFSET_EPSILON)) {
+    aData->mAnimatedGeometryRootPosition = animatedGeometryRootTopLeft;
+    InvalidateEntirePaintedLayer(aLayer, aAnimatedGeometryRoot, "subpixel offset");
+  } else if (didResetScrollPositionForLayerPixelAlignment) {
+    aData->mAnimatedGeometryRootPosition = animatedGeometryRootTopLeft;
+  }
+#else
+  Unused << didResetScrollPositionForLayerPixelAlignment;
+#endif
+}
+
+#if defined(DEBUG) || defined(MOZ_DUMP_PAINTING)
+/**
+ * Returns the appunits per dev pixel for the item's frame
+ */
+static int32_t
+AppUnitsPerDevPixel(nsDisplayItem* aItem)
+{
+  // The underlying frame for zoom items is the root frame of the subdocument.
+  // But zoom display items report their bounds etc using the parent document's
+  // APD because zoom items act as a conversion layer between the two different
+  // APDs.
+  if (aItem->GetType() == nsDisplayItem::TYPE_ZOOM) {
+    return static_cast<nsDisplayZoom*>(aItem)->GetParentAppUnitsPerDevPixel();
+  }
+  return aItem->Frame()->PresContext()->AppUnitsPerDevPixel();
+}
+#endif
+
+/**
+ * Set the visible region for aLayer.
+ * aOuterVisibleRegion is the visible region relative to the parent layer.
+ * aLayerContentsVisibleRect, if non-null, is a rectangle in the layer's
+ * own coordinate system to which the layer's visible region is restricted.
+ * Consumes *aOuterVisibleRegion.
+ */
+static void
+SetOuterVisibleRegion(Layer* aLayer, nsIntRegion* aOuterVisibleRegion,
+                      const nsIntRect* aLayerContentsVisibleRect = nullptr,
+                      bool aOuterUntransformed = false)
+{
+  Matrix4x4 transform = aLayer->GetTransform();
+  Matrix transform2D;
+  if (aOuterUntransformed) {
+    if (aLayerContentsVisibleRect) {
+      aOuterVisibleRegion->And(*aOuterVisibleRegion,
+                               *aLayerContentsVisibleRect);
+    }
+  } else if (transform.Is2D(&transform2D) && !transform2D.HasNonIntegerTranslation()) {
+    aOuterVisibleRegion->MoveBy(-int(transform2D._31), -int(transform2D._32));
+    if (aLayerContentsVisibleRect) {
+      aOuterVisibleRegion->And(*aOuterVisibleRegion, *aLayerContentsVisibleRect);
+    }
+  } else {
+    nsIntRect outerRect = aOuterVisibleRegion->GetBounds();
+    // if 'transform' is not invertible, then nothing will be displayed
+    // for the layer, so it doesn't really matter what we do here
+    Rect outerVisible(outerRect.x, outerRect.y, outerRect.width, outerRect.height);
+    transform.Invert();
+
+    Rect layerContentsVisible(-float(INT32_MAX) / 2, -float(INT32_MAX) / 2,
+                              float(INT32_MAX), float(INT32_MAX));
+    if (aLayerContentsVisibleRect) {
+      NS_ASSERTION(aLayerContentsVisibleRect->width >= 0 &&
+                   aLayerContentsVisibleRect->height >= 0,
+                   "Bad layer contents rectangle");
+      // restrict to aLayerContentsVisibleRect before call GfxRectToIntRect,
+      // in case layerVisible is extremely large (as it can be when
+      // projecting through the inverse of a 3D transform)
+      layerContentsVisible = Rect(
+          aLayerContentsVisibleRect->x, aLayerContentsVisibleRect->y,
+          aLayerContentsVisibleRect->width, aLayerContentsVisibleRect->height);
+    }
+    gfxRect layerVisible = ThebesRect(transform.ProjectRectBounds(outerVisible, layerContentsVisible));
+    layerVisible.RoundOut();
+    nsIntRect visRect;
+    if (gfxUtils::GfxRectToIntRect(layerVisible, &visRect)) {
+      *aOuterVisibleRegion = visRect;
+    } else  {
+      aOuterVisibleRegion->SetEmpty();
+    }
+  }
+
+  aLayer->SetVisibleRegion(LayerIntRegion::FromUnknownRegion(*aOuterVisibleRegion));
+}
+
+void
+ContainerState::SetOuterVisibleRegionForLayer(Layer* aLayer,
+                                              const nsIntRegion& aOuterVisibleRegion,
+                                              const nsIntRect* aLayerContentsVisibleRect,
+                                              bool aOuterUntransformed) const
+{
+  nsIntRegion visRegion = aOuterVisibleRegion;
+  if (!aOuterUntransformed) {
+    visRegion.MoveBy(mParameters.mOffset);
+  }
+  SetOuterVisibleRegion(aLayer, &visRegion, aLayerContentsVisibleRect,
+                        aOuterUntransformed);
+}
+
+nscolor
+ContainerState::FindOpaqueBackgroundColorInLayer(const PaintedLayerData* aData,
+                                                 const nsIntRect& aRect,
+                                                 bool* aOutIntersectsLayer) const
+{
+  *aOutIntersectsLayer = true;
+
+  // Scan the candidate's display items.
+  nsIntRect deviceRect = aRect;
+  nsRect appUnitRect = ToAppUnits(deviceRect, mAppUnitsPerDevPixel);
+  appUnitRect.ScaleInverseRoundOut(mParameters.mXScale, mParameters.mYScale);
+
+  for (auto& assignedItem : Reversed(aData->mAssignedDisplayItems)) {
+    nsDisplayItem* item = assignedItem.mItem;
+    bool snap;
+    nsRect bounds = item->GetBounds(mBuilder, &snap);
+    if (snap && mSnappingEnabled) {
+      nsIntRect snappedBounds = ScaleToNearestPixels(bounds);
+      if (!snappedBounds.Intersects(deviceRect))
+        continue;
+
+      if (!snappedBounds.Contains(deviceRect))
+        return NS_RGBA(0,0,0,0);
+
+    } else {
+      // The layer's visible rect is already (close enough to) pixel
+      // aligned, so no need to round out and in here.
+      if (!bounds.Intersects(appUnitRect))
+        continue;
+
+      if (!bounds.Contains(appUnitRect))
+        return NS_RGBA(0,0,0,0);
+    }
+
+    if (item->IsInvisibleInRect(appUnitRect)) {
+      continue;
+    }
+
+    if (assignedItem.mClip.IsRectAffectedByClip(deviceRect,
+                                                mParameters.mXScale,
+                                                mParameters.mYScale,
+                                                mAppUnitsPerDevPixel)) {
+      return NS_RGBA(0,0,0,0);
+    }
+
+    Maybe<nscolor> color = item->IsUniform(mBuilder);
+    if (color && NS_GET_A(*color) == 255)
+      return *color;
+
+    return NS_RGBA(0,0,0,0);
+  }
+
+  *aOutIntersectsLayer = false;
+  return NS_RGBA(0,0,0,0);
+}
+
+nscolor
+PaintedLayerDataNode::FindOpaqueBackgroundColor(const nsIntRegion& aTargetVisibleRegion,
+                                                int32_t aUnderIndex) const
+{
+  if (aUnderIndex == ABOVE_TOP) {
+    aUnderIndex = mPaintedLayerDataStack.Length();
+  }
+  for (int32_t i = aUnderIndex - 1; i >= 0; --i) {
+    const PaintedLayerData* candidate = &mPaintedLayerDataStack[i];
+    if (candidate->VisibleAboveRegionIntersects(aTargetVisibleRegion)) {
+      // Some non-PaintedLayer content between target and candidate; this is
+      // hopeless
+      return NS_RGBA(0,0,0,0);
+    }
+
+    if (!candidate->VisibleRegionIntersects(aTargetVisibleRegion)) {
+      // The layer doesn't intersect our target, ignore it and move on
+      continue;
+    }
+
+    bool intersectsLayer = true;
+    nsIntRect rect = aTargetVisibleRegion.GetBounds();
+    nscolor color = mTree.ContState().FindOpaqueBackgroundColorInLayer(
+                                        candidate, rect, &intersectsLayer);
+    if (!intersectsLayer) {
+      continue;
+    }
+    return color;
+  }
+  if (mAllDrawingAboveBackground ||
+      !mVisibleAboveBackgroundRegion.Intersect(aTargetVisibleRegion).IsEmpty()) {
+    // Some non-PaintedLayer content is between this node's background and target.
+    return NS_RGBA(0,0,0,0);
+  }
+  return FindOpaqueBackgroundColorInParentNode();
+}
+
+nscolor
+PaintedLayerDataNode::FindOpaqueBackgroundColorCoveringEverything() const
+{
+  if (!mPaintedLayerDataStack.IsEmpty() ||
+      mAllDrawingAboveBackground ||
+      !mVisibleAboveBackgroundRegion.IsEmpty()) {
+    return NS_RGBA(0,0,0,0);
+  }
+  return FindOpaqueBackgroundColorInParentNode();
+}
+
+nscolor
+PaintedLayerDataNode::FindOpaqueBackgroundColorInParentNode() const
+{
+  if (mParent) {
+    if (mHasClip) {
+      // Check whether our parent node has uniform content behind our whole
+      // clip.
+      // There's one tricky case here: If our parent node is also a scrollable,
+      // and is currently scrolled in such a way that this inner one is
+      // clipped by it, then it's not really clear how we should determine
+      // whether we have a uniform background in the parent: There might be
+      // non-uniform content in the parts that our scroll port covers in the
+      // parent and that are currently outside the parent's clip.
+      // For now, we'll fail to pull a background color in that case.
+      return mParent->FindOpaqueBackgroundColor(mClipRect);
+    }
+    return mParent->FindOpaqueBackgroundColorCoveringEverything();
+  }
+  // We are the root.
+  return mTree.UniformBackgroundColor();
+}
+
+void
+PaintedLayerData::UpdateCommonClipCount(
+    const DisplayItemClip& aCurrentClip)
+{
+  if (mCommonClipCount >= 0) {
+    mCommonClipCount = mItemClip.GetCommonRoundedRectCount(aCurrentClip, mCommonClipCount);
+  } else {
+    // first item in the layer
+    mCommonClipCount = aCurrentClip.GetRoundedRectCount();
+  }
+}
+
+bool
+PaintedLayerData::CanOptimizeToImageLayer(nsDisplayListBuilder* aBuilder)
+{
+  if (!mImage) {
+    return false;
+  }
+
+  return mImage->CanOptimizeToImageLayer(mLayer->Manager(), aBuilder);
+}
+
+already_AddRefed<ImageContainer>
+PaintedLayerData::GetContainerForImageLayer(nsDisplayListBuilder* aBuilder)
+{
+  if (!mImage) {
+    return nullptr;
+  }
+
+  return mImage->GetContainer(mLayer->Manager(), aBuilder);
+}
+
+PaintedLayerDataNode::PaintedLayerDataNode(PaintedLayerDataTree& aTree,
+                                           PaintedLayerDataNode* aParent,
+                                           AnimatedGeometryRoot* aAnimatedGeometryRoot)
+  : mTree(aTree)
+  , mParent(aParent)
+  , mAnimatedGeometryRoot(aAnimatedGeometryRoot)
+  , mAllDrawingAboveBackground(false)
+{
+  MOZ_ASSERT(nsLayoutUtils::IsAncestorFrameCrossDoc(mTree.Builder()->RootReferenceFrame(), *mAnimatedGeometryRoot));
+  mHasClip = mTree.IsClippedWithRespectToParentAnimatedGeometryRoot(mAnimatedGeometryRoot, &mClipRect);
+}
+
+PaintedLayerDataNode::~PaintedLayerDataNode()
+{
+  MOZ_ASSERT(mPaintedLayerDataStack.IsEmpty());
+  MOZ_ASSERT(mChildren.IsEmpty());
+}
+
+PaintedLayerDataNode*
+PaintedLayerDataNode::AddChildNodeFor(AnimatedGeometryRoot* aAnimatedGeometryRoot)
+{
+  MOZ_ASSERT(aAnimatedGeometryRoot->mParentAGR == mAnimatedGeometryRoot);
+  UniquePtr<PaintedLayerDataNode> child =
+    MakeUnique<PaintedLayerDataNode>(mTree, this, aAnimatedGeometryRoot);
+  mChildren.AppendElement(Move(child));
+  return mChildren.LastElement().get();
+}
+
+template<typename NewPaintedLayerCallbackType>
+PaintedLayerData*
+PaintedLayerDataNode::FindPaintedLayerFor(const nsIntRect& aVisibleRect,
+                                          bool aBackfaceHidden,
+                                          const DisplayItemScrollClip* aScrollClip,
+                                          NewPaintedLayerCallbackType aNewPaintedLayerCallback)
+{
+  if (!mPaintedLayerDataStack.IsEmpty()) {
+    PaintedLayerData* lowestUsableLayer = nullptr;
+    for (auto& data : Reversed(mPaintedLayerDataStack)) {
+      if (data.mVisibleAboveRegion.Intersects(aVisibleRect)) {
+        break;
+      }
+      if (data.mBackfaceHidden == aBackfaceHidden &&
+          data.mScrollClip == aScrollClip) {
+        lowestUsableLayer = &data;
+      }
+      nsIntRegion visibleRegion = data.mVisibleRegion;
+      // Also check whether the event-regions intersect the visible rect,
+      // unless we're in an inactive layer, in which case the event-regions
+      // will be hoisted out into their own layer.
+      // For performance reasons, we check the intersection with the bounds
+      // of the event-regions.
+      if (!mTree.ContState().IsInInactiveLayer() &&
+          (data.mScaledHitRegionBounds.Intersects(aVisibleRect) ||
+           data.mScaledMaybeHitRegionBounds.Intersects(aVisibleRect))) {
+        break;
+      }
+      if (visibleRegion.Intersects(aVisibleRect)) {
+        break;
+      }
+    }
+    if (lowestUsableLayer) {
+      return lowestUsableLayer;
+    }
+  }
+  return mPaintedLayerDataStack.AppendElement(aNewPaintedLayerCallback());
+}
+
+void
+PaintedLayerDataNode::FinishChildrenIntersecting(const nsIntRect& aRect)
+{
+  for (int32_t i = mChildren.Length() - 1; i >= 0; i--) {
+    if (mChildren[i]->Intersects(aRect)) {
+      mChildren[i]->Finish(true);
+      mChildren.RemoveElementAt(i);
+    }
+  }
+}
+
+void
+PaintedLayerDataNode::FinishAllChildren(bool aThisNodeNeedsAccurateVisibleAboveRegion)
+{
+  for (int32_t i = mChildren.Length() - 1; i >= 0; i--) {
+    mChildren[i]->Finish(aThisNodeNeedsAccurateVisibleAboveRegion);
+  }
+  mChildren.Clear();
+}
+
+void
+PaintedLayerDataNode::Finish(bool aParentNeedsAccurateVisibleAboveRegion)
+{
+  // Skip "visible above region" maintenance, because this node is going away.
+  FinishAllChildren(false);
+
+  PopAllPaintedLayerData();
+
+  if (mParent && aParentNeedsAccurateVisibleAboveRegion) {
+    if (mHasClip) {
+      mParent->AddToVisibleAboveRegion(mClipRect);
+    } else {
+      mParent->SetAllDrawingAbove();
+    }
+  }
+  mTree.NodeWasFinished(mAnimatedGeometryRoot);
+}
+
+void
+PaintedLayerDataNode::AddToVisibleAboveRegion(const nsIntRect& aRect)
+{
+  nsIntRegion& visibleAboveRegion = mPaintedLayerDataStack.IsEmpty()
+    ? mVisibleAboveBackgroundRegion
+    : mPaintedLayerDataStack.LastElement().mVisibleAboveRegion;
+  visibleAboveRegion.Or(visibleAboveRegion, aRect);
+  visibleAboveRegion.SimplifyOutward(8);
+}
+
+void
+PaintedLayerDataNode::SetAllDrawingAbove()
+{
+  PopAllPaintedLayerData();
+  mAllDrawingAboveBackground = true;
+  mVisibleAboveBackgroundRegion.SetEmpty();
+}
+
+void
+PaintedLayerDataNode::PopPaintedLayerData()
+{
+  MOZ_ASSERT(!mPaintedLayerDataStack.IsEmpty());
+  size_t lastIndex = mPaintedLayerDataStack.Length() - 1;
+  PaintedLayerData& data = mPaintedLayerDataStack[lastIndex];
+  mTree.ContState().FinishPaintedLayerData(data, [this, &data, lastIndex]() {
+    return this->FindOpaqueBackgroundColor(data.mVisibleRegion, lastIndex);
+  });
+  mPaintedLayerDataStack.RemoveElementAt(lastIndex);
+}
+
+void
+PaintedLayerDataNode::PopAllPaintedLayerData()
+{
+  while (!mPaintedLayerDataStack.IsEmpty()) {
+    PopPaintedLayerData();
+  }
+}
+
+nsDisplayListBuilder*
+PaintedLayerDataTree::Builder() const
+{
+  return mContainerState.Builder();
+}
+
+void
+PaintedLayerDataTree::Finish()
+{
+  if (mRoot) {
+    mRoot->Finish(false);
+  }
+  MOZ_ASSERT(mNodes.Count() == 0);
+  mRoot = nullptr;
+}
+
+void
+PaintedLayerDataTree::NodeWasFinished(AnimatedGeometryRoot* aAnimatedGeometryRoot)
+{
+  mNodes.Remove(aAnimatedGeometryRoot);
+}
+
+void
+PaintedLayerDataTree::AddingOwnLayer(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                     const nsIntRect* aRect,
+                                     nscolor* aOutUniformBackgroundColor)
+{
+  FinishPotentiallyIntersectingNodes(aAnimatedGeometryRoot, aRect);
+  PaintedLayerDataNode* node = EnsureNodeFor(aAnimatedGeometryRoot);
+  if (aRect) {
+    if (aOutUniformBackgroundColor) {
+      *aOutUniformBackgroundColor = node->FindOpaqueBackgroundColor(*aRect);
+    }
+    node->AddToVisibleAboveRegion(*aRect);
+  } else {
+    if (aOutUniformBackgroundColor) {
+      *aOutUniformBackgroundColor = node->FindOpaqueBackgroundColorCoveringEverything();
+    }
+    node->SetAllDrawingAbove();
+  }
+}
+
+template<typename NewPaintedLayerCallbackType>
+PaintedLayerData*
+PaintedLayerDataTree::FindPaintedLayerFor(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                          const DisplayItemScrollClip* aScrollClip,
+                                          const nsIntRect& aVisibleRect,
+                                          bool aBackfaceHidden,
+                                          NewPaintedLayerCallbackType aNewPaintedLayerCallback)
+{
+  const nsIntRect* bounds = &aVisibleRect;
+  FinishPotentiallyIntersectingNodes(aAnimatedGeometryRoot, bounds);
+  PaintedLayerDataNode* node = EnsureNodeFor(aAnimatedGeometryRoot);
+
+  PaintedLayerData* data =
+    node->FindPaintedLayerFor(aVisibleRect, aBackfaceHidden, aScrollClip,
+                              aNewPaintedLayerCallback);
+  return data;
+}
+
+void
+PaintedLayerDataTree::FinishPotentiallyIntersectingNodes(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                                         const nsIntRect* aRect)
+{
+  AnimatedGeometryRoot* ancestorThatIsChildOfCommonAncestor = nullptr;
+  PaintedLayerDataNode* ancestorNode =
+    FindNodeForAncestorAnimatedGeometryRoot(aAnimatedGeometryRoot,
+                                            &ancestorThatIsChildOfCommonAncestor);
+  if (!ancestorNode) {
+    // None of our ancestors are in the tree. This should only happen if this
+    // is the very first item we're looking at.
+    MOZ_ASSERT(!mRoot);
+    return;
+  }
+
+  if (ancestorNode->GetAnimatedGeometryRoot() == aAnimatedGeometryRoot) {
+    // aAnimatedGeometryRoot already has a node in the tree.
+    // This is the common case.
+    MOZ_ASSERT(!ancestorThatIsChildOfCommonAncestor);
+    if (aRect) {
+      ancestorNode->FinishChildrenIntersecting(*aRect);
+    } else {
+      ancestorNode->FinishAllChildren();
+    }
+    return;
+  }
+
+  // We have found an existing ancestor, but it's a proper ancestor of our
+  // animated geometry root.
+  // ancestorThatIsChildOfCommonAncestor is the last animated geometry root
+  // encountered on the way up from aAnimatedGeometryRoot to ancestorNode.
+  MOZ_ASSERT(ancestorThatIsChildOfCommonAncestor);
+  MOZ_ASSERT(nsLayoutUtils::IsAncestorFrameCrossDoc(*ancestorThatIsChildOfCommonAncestor, *aAnimatedGeometryRoot));
+  MOZ_ASSERT(ancestorThatIsChildOfCommonAncestor->mParentAGR == ancestorNode->GetAnimatedGeometryRoot());
+
+  // ancestorThatIsChildOfCommonAncestor is not in the tree yet!
+  MOZ_ASSERT(!mNodes.Get(ancestorThatIsChildOfCommonAncestor));
+
+  // We're about to add a node for ancestorThatIsChildOfCommonAncestor, so we
+  // finish all intersecting siblings.
+  nsIntRect clip;
+  if (IsClippedWithRespectToParentAnimatedGeometryRoot(ancestorThatIsChildOfCommonAncestor, &clip)) {
+    ancestorNode->FinishChildrenIntersecting(clip);
+  } else {
+    ancestorNode->FinishAllChildren();
+  }
+}
+
+PaintedLayerDataNode*
+PaintedLayerDataTree::EnsureNodeFor(AnimatedGeometryRoot* aAnimatedGeometryRoot)
+{
+  MOZ_ASSERT(aAnimatedGeometryRoot);
+  PaintedLayerDataNode* node = mNodes.Get(aAnimatedGeometryRoot);
+  if (node) {
+    return node;
+  }
+
+  AnimatedGeometryRoot* parentAnimatedGeometryRoot = aAnimatedGeometryRoot->mParentAGR;
+  if (!parentAnimatedGeometryRoot) {
+    MOZ_ASSERT(!mRoot);
+    MOZ_ASSERT(*aAnimatedGeometryRoot == Builder()->RootReferenceFrame());
+    mRoot = MakeUnique<PaintedLayerDataNode>(*this, nullptr, aAnimatedGeometryRoot);
+    node = mRoot.get();
+  } else {
+    PaintedLayerDataNode* parentNode = EnsureNodeFor(parentAnimatedGeometryRoot);
+    MOZ_ASSERT(parentNode);
+    node = parentNode->AddChildNodeFor(aAnimatedGeometryRoot);
+  }
+  MOZ_ASSERT(node);
+  mNodes.Put(aAnimatedGeometryRoot, node);
+  return node;
+}
+
+bool
+PaintedLayerDataTree::IsClippedWithRespectToParentAnimatedGeometryRoot(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                                                       nsIntRect* aOutClip)
+{
+  nsIScrollableFrame* scrollableFrame = nsLayoutUtils::GetScrollableFrameFor(*aAnimatedGeometryRoot);
+  if (!scrollableFrame) {
+    return false;
+  }
+  nsIFrame* scrollFrame = do_QueryFrame(scrollableFrame);
+  nsRect scrollPort = scrollableFrame->GetScrollPortRect() + Builder()->ToReferenceFrame(scrollFrame);
+  *aOutClip = mContainerState.ScaleToNearestPixels(scrollPort);
+  return true;
+}
+
+PaintedLayerDataNode*
+PaintedLayerDataTree::FindNodeForAncestorAnimatedGeometryRoot(AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                                              AnimatedGeometryRoot** aOutAncestorChild)
+{
+  if (!aAnimatedGeometryRoot) {
+    return nullptr;
+  }
+  PaintedLayerDataNode* node = mNodes.Get(aAnimatedGeometryRoot);
+  if (node) {
+    return node;
+  }
+  *aOutAncestorChild = aAnimatedGeometryRoot;
+  return FindNodeForAncestorAnimatedGeometryRoot(aAnimatedGeometryRoot->mParentAGR, aOutAncestorChild);
+}
+
+static bool
+CanOptimizeAwayPaintedLayer(PaintedLayerData* aData,
+                           FrameLayerBuilder* aLayerBuilder)
+{
+  if (!aLayerBuilder->IsBuildingRetainedLayers()) {
+    return false;
+  }
+
+  // If there's no painted layer with valid content in it that we can reuse,
+  // always create a color or image layer (and potentially throw away an
+  // existing completely invalid painted layer).
+  if (aData->mLayer->GetValidRegion().IsEmpty()) {
+    return true;
+  }
+
+  // There is an existing painted layer we can reuse. Throwing it away can make
+  // compositing cheaper (see bug 946952), but it might cause us to re-allocate
+  // the painted layer frequently due to an animation. So we only discard it if
+  // we're in tree compression mode, which is triggered at a low frequency.
+  return aLayerBuilder->CheckInLayerTreeCompressionMode();
+}
+
+#ifdef DEBUG
+static int32_t FindIndexOfLayerIn(nsTArray<NewLayerEntry>& aArray,
+                                  Layer* aLayer)
+{
+  for (uint32_t i = 0; i < aArray.Length(); ++i) {
+    if (aArray[i].mLayer == aLayer) {
+      return i;
+    }
+  }
+  return -1;
+}
+#endif
+
+already_AddRefed<Layer>
+ContainerState::PrepareImageLayer(PaintedLayerData* aData)
+{
+  RefPtr<ImageContainer> imageContainer =
+    aData->GetContainerForImageLayer(mBuilder);
+  if (!imageContainer) {
+    return nullptr;
+  }
+
+  RefPtr<ImageLayer> imageLayer = CreateOrRecycleImageLayer(aData->mLayer);
+  imageLayer->SetContainer(imageContainer);
+  aData->mImage->ConfigureLayer(imageLayer, mParameters);
+  imageLayer->SetPostScale(mParameters.mXScale,
+                           mParameters.mYScale);
+
+  if (aData->mItemClip.HasClip()) {
+    ParentLayerIntRect clip =
+      ViewAs<ParentLayerPixel>(ScaleToNearestPixels(aData->mItemClip.GetClipRect()));
+    clip.MoveBy(ViewAs<ParentLayerPixel>(mParameters.mOffset));
+    imageLayer->SetClipRect(Some(clip));
+  } else {
+    imageLayer->SetClipRect(Nothing());
+  }
+
+  mLayerBuilder->StoreOptimizedLayerForFrame(aData->mImage, imageLayer);
+  FLB_LOG_PAINTED_LAYER_DECISION(aData,
+                                 "  Selected image layer=%p\n", imageLayer.get());
+
+  return imageLayer.forget();
+}
+
+already_AddRefed<Layer>
+ContainerState::PrepareColorLayer(PaintedLayerData* aData)
+{
+  RefPtr<ColorLayer> colorLayer = CreateOrRecycleColorLayer(aData->mLayer);
+  colorLayer->SetColor(Color::FromABGR(aData->mSolidColor));
+
+  // Copy transform
+  colorLayer->SetBaseTransform(aData->mLayer->GetBaseTransform());
+  colorLayer->SetPostScale(aData->mLayer->GetPostXScale(),
+                           aData->mLayer->GetPostYScale());
+
+  nsIntRect visibleRect = aData->mVisibleRegion.GetBounds();
+  visibleRect.MoveBy(-GetTranslationForPaintedLayer(aData->mLayer));
+  colorLayer->SetBounds(visibleRect);
+  colorLayer->SetClipRect(Nothing());
+
+  FLB_LOG_PAINTED_LAYER_DECISION(aData,
+                                 "  Selected color layer=%p\n", colorLayer.get());
+
+  return colorLayer.forget();
+}
+
+static void
+SetBackfaceHiddenForLayer(bool aBackfaceHidden, Layer* aLayer)
+{
+  if (aBackfaceHidden) {
+    aLayer->SetContentFlags(aLayer->GetContentFlags() |
+                            Layer::CONTENT_BACKFACE_HIDDEN);
+  } else {
+    aLayer->SetContentFlags(aLayer->GetContentFlags() &
+                            ~Layer::CONTENT_BACKFACE_HIDDEN);
+  }
+}
+
+template<typename FindOpaqueBackgroundColorCallbackType>
+void ContainerState::FinishPaintedLayerData(PaintedLayerData& aData, FindOpaqueBackgroundColorCallbackType aFindOpaqueBackgroundColor)
+{
+  PaintedLayerData* data = &aData;
+
+  if (!data->mLayer) {
+    // No layer was recycled, so we create a new one.
+    RefPtr<PaintedLayer> paintedLayer = CreatePaintedLayer(data);
+    data->mLayer = paintedLayer;
+
+    NS_ASSERTION(FindIndexOfLayerIn(mNewChildLayers, paintedLayer) < 0,
+                 "Layer already in list???");
+    mNewChildLayers[data->mNewChildLayersIndex].mLayer = paintedLayer.forget();
+  }
+
+  for (auto& item : data->mAssignedDisplayItems) {
+    MOZ_ASSERT(item.mItem->GetType() != nsDisplayItem::TYPE_LAYER_EVENT_REGIONS);
+
+    InvalidateForLayerChange(item.mItem, data->mLayer);
+    mLayerBuilder->AddPaintedDisplayItem(data, item.mItem, item.mClip,
+                                         *this, item.mLayerState,
+                                         data->mAnimatedGeometryRootOffset);
+  }
+
+  NewLayerEntry* newLayerEntry = &mNewChildLayers[data->mNewChildLayersIndex];
+
+  RefPtr<Layer> layer;
+  bool canOptimizeToImageLayer = data->CanOptimizeToImageLayer(mBuilder);
+
+  FLB_LOG_PAINTED_LAYER_DECISION(data, "Selecting layer for pld=%p\n", data);
+  FLB_LOG_PAINTED_LAYER_DECISION(data, "  Solid=%i, hasImage=%c, canOptimizeAwayPaintedLayer=%i\n",
+          data->mIsSolidColorInVisibleRegion, canOptimizeToImageLayer ? 'y' : 'n',
+          CanOptimizeAwayPaintedLayer(data, mLayerBuilder));
+
+  if ((data->mIsSolidColorInVisibleRegion || canOptimizeToImageLayer) &&
+      CanOptimizeAwayPaintedLayer(data, mLayerBuilder)) {
+    NS_ASSERTION(!(data->mIsSolidColorInVisibleRegion && canOptimizeToImageLayer),
+                 "Can't be a solid color as well as an image!");
+
+    layer = canOptimizeToImageLayer ? PrepareImageLayer(data)
+                                    : PrepareColorLayer(data);
+
+    if (layer) {
+      NS_ASSERTION(FindIndexOfLayerIn(mNewChildLayers, layer) < 0,
+                   "Layer already in list???");
+      NS_ASSERTION(newLayerEntry->mLayer == data->mLayer,
+                   "Painted layer at wrong index");
+      // Store optimized layer in reserved slot
+      newLayerEntry = &mNewChildLayers[data->mNewChildLayersIndex + 1];
+      NS_ASSERTION(!newLayerEntry->mLayer, "Slot already occupied?");
+      newLayerEntry->mLayer = layer;
+      newLayerEntry->mAnimatedGeometryRoot = data->mAnimatedGeometryRoot;
+      newLayerEntry->mScrollClip = data->mScrollClip;
+
+      // Hide the PaintedLayer. We leave it in the layer tree so that we
+      // can find and recycle it later.
+      ParentLayerIntRect emptyRect;
+      data->mLayer->SetClipRect(Some(emptyRect));
+      data->mLayer->SetVisibleRegion(LayerIntRegion());
+      data->mLayer->InvalidateRegion(data->mLayer->GetValidRegion().GetBounds());
+      data->mLayer->SetEventRegions(EventRegions());
+    }
+  }
+
+  if (!layer) {
+    // We couldn't optimize to an image layer or a color layer above.
+    layer = data->mLayer;
+    layer->SetClipRect(Nothing());
+    FLB_LOG_PAINTED_LAYER_DECISION(data, "  Selected painted layer=%p\n", layer.get());
+  }
+
+  // If the layer is a fixed background layer, the clip on the fixed background
+  // display item was not applied to the opaque region in
+  // ContainerState::ComputeOpaqueRect(), but was saved in data->mItemClip.
+  // Apply it to the opaque region now. Note that it's important to do this
+  // before the opaque region is propagated to the NewLayerEntry below.
+  if (data->mSingleItemFixedToViewport && data->mItemClip.HasClip()) {
+    nsRect clipRect = data->mItemClip.GetClipRect();
+    nsRect insideRoundedCorners = data->mItemClip.ApproximateIntersectInward(clipRect);
+    nsIntRect insideRoundedCornersScaled = ScaleToInsidePixels(insideRoundedCorners);
+    data->mOpaqueRegion.AndWith(insideRoundedCornersScaled);
+  }
+
+  if (mLayerBuilder->IsBuildingRetainedLayers()) {
+    newLayerEntry->mVisibleRegion = data->mVisibleRegion;
+    newLayerEntry->mOpaqueRegion = data->mOpaqueRegion;
+    newLayerEntry->mHideAllLayersBelow = data->mHideAllLayersBelow;
+    newLayerEntry->mOpaqueForAnimatedGeometryRootParent = data->mOpaqueForAnimatedGeometryRootParent;
+  } else {
+    SetOuterVisibleRegionForLayer(layer, data->mVisibleRegion);
+  }
+
+  nsIntRect layerBounds = data->mBounds;
+  layerBounds.MoveBy(-GetTranslationForPaintedLayer(data->mLayer));
+  layer->SetLayerBounds(layerBounds);
+
+#ifdef MOZ_DUMP_PAINTING
+  if (!data->mLog.IsEmpty()) {
+    if (PaintedLayerData* containingPld = mLayerBuilder->GetContainingPaintedLayerData()) {
+      containingPld->mLayer->AddExtraDumpInfo(nsCString(data->mLog));
+    } else {
+      layer->AddExtraDumpInfo(nsCString(data->mLog));
+    }
+  }
+#endif
+
+  nsIntRegion transparentRegion;
+  transparentRegion.Sub(data->mVisibleRegion, data->mOpaqueRegion);
+  bool isOpaque = transparentRegion.IsEmpty();
+  // For translucent PaintedLayers, try to find an opaque background
+  // color that covers the entire area beneath it so we can pull that
+  // color into this layer to make it opaque.
+  if (layer == data->mLayer) {
+    nscolor backgroundColor = NS_RGBA(0,0,0,0);
+    if (!isOpaque) {
+      backgroundColor = aFindOpaqueBackgroundColor();
+      if (NS_GET_A(backgroundColor) == 255) {
+        isOpaque = true;
+      }
+    }
+
+    // Store the background color
+    PaintedDisplayItemLayerUserData* userData =
+      GetPaintedDisplayItemLayerUserData(data->mLayer);
+    NS_ASSERTION(userData, "where did our user data go?");
+    if (userData->mForcedBackgroundColor != backgroundColor) {
+      // Invalidate the entire target PaintedLayer since we're changing
+      // the background color
+#ifdef MOZ_DUMP_PAINTING
+      if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+        printf_stderr("Forced background color has changed from #%08X to #%08X on layer %p\n",
+                      userData->mForcedBackgroundColor, backgroundColor, data->mLayer);
+        nsAutoCString str;
+        AppendToString(str, data->mLayer->GetValidRegion());
+        printf_stderr("Invalidating layer %p: %s\n", data->mLayer, str.get());
+      }
+#endif
+      data->mLayer->InvalidateRegion(data->mLayer->GetValidRegion());
+    }
+    userData->mForcedBackgroundColor = backgroundColor;
+
+    userData->mFontSmoothingBackgroundColor = data->mFontSmoothingBackgroundColor;
+
+    // use a mask layer for rounded rect clipping.
+    // data->mCommonClipCount may be -1 if we haven't put any actual
+    // drawable items in this layer (i.e. it's only catching events).
+    int32_t commonClipCount;
+    // If the layer contains a single item fixed to the viewport, we removed
+    // its clip in ProcessDisplayItems() and saved it to set on the layer instead.
+    // Set the clip on the layer now.
+    if (data->mSingleItemFixedToViewport && data->mItemClip.HasClip()) {
+      nsIntRect layerClipRect = ScaleToNearestPixels(data->mItemClip.GetClipRect());
+      layerClipRect.MoveBy(mParameters.mOffset);
+      // The clip from such an item becomes part of the layer's scrolled clip,
+      // and the associated mask layer one of the layer's "ancestor mask layers".
+      LayerClip scrolledClip;
+      scrolledClip.SetClipRect(ViewAs<ParentLayerPixel>(layerClipRect));
+      scrolledClip.SetMaskLayerIndex(
+          SetupMaskLayerForScrolledClip(data->mLayer, data->mItemClip));
+      data->mLayer->SetScrolledClip(Some(scrolledClip));
+      // There is only one item, so all of the clips are in common to all items.
+      // data->mCommonClipCount will be zero because we removed the clip from
+      // the display item. (It could also be -1 if we're inside an inactive
+      // layer tree in which we don't call UpdateCommonClipCount() at all.)
+      MOZ_ASSERT(data->mCommonClipCount == -1 || data->mCommonClipCount == 0);
+      commonClipCount = data->mItemClip.GetRoundedRectCount();
+    } else {
+      commonClipCount = std::max(0, data->mCommonClipCount);
+      SetupMaskLayer(layer, data->mItemClip, commonClipCount);
+    }
+    // copy commonClipCount to the entry
+    FrameLayerBuilder::PaintedLayerItemsEntry* entry = mLayerBuilder->
+      GetPaintedLayerItemsEntry(static_cast<PaintedLayer*>(layer.get()));
+    entry->mCommonClipCount = commonClipCount;
+  } else {
+    // mask layer for image and color layers
+    SetupMaskLayer(layer, data->mItemClip);
+  }
+
+  uint32_t flags = 0;
+  nsIWidget* widget = mContainerReferenceFrame->PresContext()->GetRootWidget();
+  // See bug 941095. Not quite ready to disable this.
+  bool hidpi = false && widget && widget->GetDefaultScale().scale >= 2;
+  if (hidpi) {
+    flags |= Layer::CONTENT_DISABLE_SUBPIXEL_AA;
+  }
+  if (isOpaque && !data->mForceTransparentSurface) {
+    flags |= Layer::CONTENT_OPAQUE;
+  } else if (data->mNeedComponentAlpha && !hidpi) {
+    flags |= Layer::CONTENT_COMPONENT_ALPHA;
+  }
+  if (data->mDisableFlattening) {
+    flags |= Layer::CONTENT_DISABLE_FLATTENING;
+  }
+  layer->SetContentFlags(flags);
+
+  PaintedLayerData* containingPaintedLayerData =
+     mLayerBuilder->GetContainingPaintedLayerData();
+  if (containingPaintedLayerData) {
+    if (!data->mDispatchToContentHitRegion.GetBounds().IsEmpty()) {
+      nsRect rect = nsLayoutUtils::TransformFrameRectToAncestor(
+        mContainerReferenceFrame,
+        data->mDispatchToContentHitRegion.GetBounds(),
+        containingPaintedLayerData->mReferenceFrame);
+      containingPaintedLayerData->mDispatchToContentHitRegion.Or(
+        containingPaintedLayerData->mDispatchToContentHitRegion, rect);
+    }
+    if (!data->mMaybeHitRegion.GetBounds().IsEmpty()) {
+      nsRect rect = nsLayoutUtils::TransformFrameRectToAncestor(
+        mContainerReferenceFrame,
+        data->mMaybeHitRegion.GetBounds(),
+        containingPaintedLayerData->mReferenceFrame);
+      containingPaintedLayerData->mMaybeHitRegion.Or(
+        containingPaintedLayerData->mMaybeHitRegion, rect);
+      containingPaintedLayerData->mMaybeHitRegion.SimplifyOutward(8);
+    }
+    Maybe<Matrix4x4> matrixCache;
+    nsLayoutUtils::TransformToAncestorAndCombineRegions(
+      data->mHitRegion,
+      mContainerReferenceFrame,
+      containingPaintedLayerData->mReferenceFrame,
+      &containingPaintedLayerData->mHitRegion,
+      &containingPaintedLayerData->mMaybeHitRegion,
+      &matrixCache);
+    // See the comment in nsDisplayList::AddFrame, where the touch action regions
+    // are handled. The same thing applies here.
+    bool alreadyHadRegions =
+        !containingPaintedLayerData->mNoActionRegion.IsEmpty() ||
+        !containingPaintedLayerData->mHorizontalPanRegion.IsEmpty() ||
+        !containingPaintedLayerData->mVerticalPanRegion.IsEmpty();
+    nsLayoutUtils::TransformToAncestorAndCombineRegions(
+      data->mNoActionRegion,
+      mContainerReferenceFrame,
+      containingPaintedLayerData->mReferenceFrame,
+      &containingPaintedLayerData->mNoActionRegion,
+      &containingPaintedLayerData->mDispatchToContentHitRegion,
+      &matrixCache);
+    nsLayoutUtils::TransformToAncestorAndCombineRegions(
+      data->mHorizontalPanRegion,
+      mContainerReferenceFrame,
+      containingPaintedLayerData->mReferenceFrame,
+      &containingPaintedLayerData->mHorizontalPanRegion,
+      &containingPaintedLayerData->mDispatchToContentHitRegion,
+      &matrixCache);
+    nsLayoutUtils::TransformToAncestorAndCombineRegions(
+      data->mVerticalPanRegion,
+      mContainerReferenceFrame,
+      containingPaintedLayerData->mReferenceFrame,
+      &containingPaintedLayerData->mVerticalPanRegion,
+      &containingPaintedLayerData->mDispatchToContentHitRegion,
+      &matrixCache);
+    if (alreadyHadRegions) {
+      containingPaintedLayerData->mDispatchToContentHitRegion.OrWith(
+        containingPaintedLayerData->CombinedTouchActionRegion());
+    }
+  } else {
+    EventRegions regions;
+    regions.mHitRegion = ScaleRegionToOutsidePixels(data->mHitRegion);
+    regions.mNoActionRegion = ScaleRegionToOutsidePixels(data->mNoActionRegion);
+    regions.mHorizontalPanRegion = ScaleRegionToOutsidePixels(data->mHorizontalPanRegion);
+    regions.mVerticalPanRegion = ScaleRegionToOutsidePixels(data->mVerticalPanRegion);
+    // Points whose hit-region status we're not sure about need to be dispatched
+    // to the content thread. If a point is in both maybeHitRegion and hitRegion
+    // then it's not a "maybe" any more, and doesn't go into the dispatch-to-
+    // content region.
+    nsIntRegion maybeHitRegion = ScaleRegionToOutsidePixels(data->mMaybeHitRegion);
+    regions.mDispatchToContentHitRegion.Sub(maybeHitRegion, regions.mHitRegion);
+    regions.mDispatchToContentHitRegion.OrWith(
+        ScaleRegionToOutsidePixels(data->mDispatchToContentHitRegion));
+    regions.mHitRegion.OrWith(maybeHitRegion);
+
+    Matrix mat = layer->GetTransform().As2D();
+    mat.Invert();
+    regions.ApplyTranslationAndScale(mat._31, mat._32, mat._11, mat._22);
+
+    layer->SetEventRegions(regions);
+  }
+
+  SetBackfaceHiddenForLayer(data->mBackfaceHidden, data->mLayer);
+  if (layer != data->mLayer) {
+    SetBackfaceHiddenForLayer(data->mBackfaceHidden, layer);
+  }
+}
+
+static bool
+IsItemAreaInWindowOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                               nsDisplayItem* aItem,
+                               const nsRect& aComponentAlphaBounds)
+{
+  if (!aItem->Frame()->PresContext()->IsChrome()) {
+    // Assume that Web content is always in the window opaque region.
+    return true;
+  }
+  if (aItem->ReferenceFrame() != aBuilder->RootReferenceFrame()) {
+    // aItem is probably in some transformed subtree.
+    // We're not going to bother figuring out where this landed, we're just
+    // going to assume it might have landed over a transparent part of
+    // the window.
+    return false;
+  }
+  return aBuilder->GetWindowOpaqueRegion().Contains(aComponentAlphaBounds);
+}
+
+void
+PaintedLayerData::Accumulate(ContainerState* aState,
+                            nsDisplayItem* aItem,
+                            const nsIntRegion& aClippedOpaqueRegion,
+                            const nsIntRect& aVisibleRect,
+                            const DisplayItemClip& aClip,
+                            LayerState aLayerState)
+{
+  FLB_LOG_PAINTED_LAYER_DECISION(this, "Accumulating dp=%s(%p), f=%p against pld=%p\n", aItem->Name(), aItem, aItem->Frame(), this);
+
+  bool snap;
+  nsRect itemBounds = aItem->GetBounds(aState->mBuilder, &snap);
+  mBounds = mBounds.Union(aState->ScaleToOutsidePixels(itemBounds, snap));
+
+  if (aState->mBuilder->NeedToForceTransparentSurfaceForItem(aItem)) {
+    mForceTransparentSurface = true;
+  }
+  if (aState->mParameters.mDisableSubpixelAntialiasingInDescendants) {
+    // Disable component alpha.
+    // Note that the transform (if any) on the PaintedLayer is always an integer translation so
+    // we don't have to factor that in here.
+    aItem->DisableComponentAlpha();
+  }
+
+  bool clipMatches = mItemClip == aClip;
+  mItemClip = aClip;
+
+  mAssignedDisplayItems.AppendElement(AssignedDisplayItem(aItem, aClip, aLayerState));
+
+  if (!mIsSolidColorInVisibleRegion && mOpaqueRegion.Contains(aVisibleRect) &&
+      mVisibleRegion.Contains(aVisibleRect) && !mImage) {
+    // A very common case! Most pages have a PaintedLayer with the page
+    // background (opaque) visible and most or all of the page content over the
+    // top of that background.
+    // The rest of this method won't do anything. mVisibleRegion and mOpaqueRegion
+    // don't need updating. mVisibleRegion contains aVisibleRect already,
+    // mOpaqueRegion contains aVisibleRect and therefore whatever the opaque
+    // region of the item is. mVisibleRegion must contain mOpaqueRegion
+    // and therefore aVisibleRect.
+    return;
+  }
+
+  /* Mark as available for conversion to image layer if this is a nsDisplayImage and
+   * it's the only thing visible in this layer.
+   */
+  if (nsIntRegion(aVisibleRect).Contains(mVisibleRegion) &&
+      aClippedOpaqueRegion.Contains(mVisibleRegion) &&
+      aItem->SupportsOptimizingToImage()) {
+    mImage = static_cast<nsDisplayImageContainer*>(aItem);
+    FLB_LOG_PAINTED_LAYER_DECISION(this, "  Tracking image: nsDisplayImageContainer covers the layer\n");
+  } else if (mImage) {
+    FLB_LOG_PAINTED_LAYER_DECISION(this, "  No longer tracking image\n");
+    mImage = nullptr;
+  }
+
+  bool isFirstVisibleItem = mVisibleRegion.IsEmpty();
+  if (isFirstVisibleItem) {
+    nscolor fontSmoothingBGColor;
+    if (aItem->ProvidesFontSmoothingBackgroundColor(&fontSmoothingBGColor)) {
+      mFontSmoothingBackgroundColor = fontSmoothingBGColor;
+    }
+  }
+
+  Maybe<nscolor> uniformColor = aItem->IsUniform(aState->mBuilder);
+
+  // Some display items have to exist (so they can set forceTransparentSurface
+  // below) but don't draw anything. They'll return true for isUniform but
+  // a color with opacity 0.
+  if (!uniformColor || NS_GET_A(*uniformColor) > 0) {
+    // Make sure that the visible area is covered by uniform pixels. In
+    // particular this excludes cases where the edges of the item are not
+    // pixel-aligned (thus the item will not be truly uniform).
+    if (uniformColor) {
+      bool snap;
+      nsRect bounds = aItem->GetBounds(aState->mBuilder, &snap);
+      if (!aState->ScaleToInsidePixels(bounds, snap).Contains(aVisibleRect)) {
+        uniformColor = Nothing();
+        FLB_LOG_PAINTED_LAYER_DECISION(this, "  Display item does not cover the visible rect\n");
+      }
+    }
+    if (uniformColor) {
+      if (isFirstVisibleItem) {
+        // This color is all we have
+        mSolidColor = *uniformColor;
+        mIsSolidColorInVisibleRegion = true;
+      } else if (mIsSolidColorInVisibleRegion &&
+                 mVisibleRegion.IsEqual(nsIntRegion(aVisibleRect)) &&
+                 clipMatches) {
+        // we can just blend the colors together
+        mSolidColor = NS_ComposeColors(mSolidColor, *uniformColor);
+      } else {
+        FLB_LOG_PAINTED_LAYER_DECISION(this, "  Layer not a solid color: Can't blend colors togethers\n");
+        mIsSolidColorInVisibleRegion = false;
+      }
+    } else {
+      FLB_LOG_PAINTED_LAYER_DECISION(this, "  Layer is not a solid color: Display item is not uniform over the visible bound\n");
+      mIsSolidColorInVisibleRegion = false;
+    }
+
+    mVisibleRegion.Or(mVisibleRegion, aVisibleRect);
+    mVisibleRegion.SimplifyOutward(4);
+  }
+
+  if (!aClippedOpaqueRegion.IsEmpty()) {
+    for (auto iter = aClippedOpaqueRegion.RectIter(); !iter.Done(); iter.Next()) {
+      // We don't use SimplifyInward here since it's not defined exactly
+      // what it will discard. For our purposes the most important case
+      // is a large opaque background at the bottom of z-order (e.g.,
+      // a canvas background), so we need to make sure that the first rect
+      // we see doesn't get discarded.
+      nsIntRegion tmp;
+      tmp.Or(mOpaqueRegion, iter.Get());
+       // Opaque display items in chrome documents whose window is partially
+       // transparent are always added to the opaque region. This helps ensure
+       // that we get as much subpixel-AA as possible in the chrome.
+       if (tmp.GetNumRects() <= 4 || aItem->Frame()->PresContext()->IsChrome()) {
+        mOpaqueRegion = Move(tmp);
+      }
+    }
+  }
+
+  if (!aState->mParameters.mDisableSubpixelAntialiasingInDescendants) {
+    nsRect componentAlpha = aItem->GetComponentAlphaBounds(aState->mBuilder);
+    if (!componentAlpha.IsEmpty()) {
+      nsIntRect componentAlphaRect =
+        aState->ScaleToOutsidePixels(componentAlpha, false).Intersect(aVisibleRect);
+      if (!mOpaqueRegion.Contains(componentAlphaRect)) {
+        if (IsItemAreaInWindowOpaqueRegion(aState->mBuilder, aItem,
+              componentAlpha.Intersect(aItem->GetVisibleRect()))) {
+          mNeedComponentAlpha = true;
+        } else {
+          aItem->DisableComponentAlpha();
+        }
+      }
+    }
+  }
+
+  // Ensure animated text does not get flattened, even if it forces other
+  // content in the container to be layerized. The content backend might
+  // not support subpixel positioning of text that animated transforms can
+  // generate. bug 633097
+  if (aState->mParameters.mInActiveTransformedSubtree &&
+       (mNeedComponentAlpha ||
+         !aItem->GetComponentAlphaBounds(aState->mBuilder).IsEmpty())) {
+    mDisableFlattening = true;
+  }
+}
+
+nsRegion
+PaintedLayerData::CombinedTouchActionRegion()
+{
+  nsRegion result;
+  result.Or(mHorizontalPanRegion, mVerticalPanRegion);
+  result.OrWith(mNoActionRegion);
+  return result;
+}
+
+void
+PaintedLayerData::AccumulateEventRegions(ContainerState* aState, nsDisplayLayerEventRegions* aEventRegions)
+{
+  FLB_LOG_PAINTED_LAYER_DECISION(this, "Accumulating event regions %p against pld=%p\n", aEventRegions, this);
+
+  mHitRegion.OrWith(aEventRegions->HitRegion());
+  mMaybeHitRegion.OrWith(aEventRegions->MaybeHitRegion());
+  mDispatchToContentHitRegion.OrWith(aEventRegions->DispatchToContentHitRegion());
+
+  // See the comment in nsDisplayList::AddFrame, where the touch action regions
+  // are handled. The same thing applies here.
+  bool alreadyHadRegions = !mNoActionRegion.IsEmpty() ||
+      !mHorizontalPanRegion.IsEmpty() ||
+      !mVerticalPanRegion.IsEmpty();
+  mNoActionRegion.OrWith(aEventRegions->NoActionRegion());
+  mHorizontalPanRegion.OrWith(aEventRegions->HorizontalPanRegion());
+  mVerticalPanRegion.OrWith(aEventRegions->VerticalPanRegion());
+  if (alreadyHadRegions) {
+    mDispatchToContentHitRegion.OrWith(CombinedTouchActionRegion());
+  }
+
+  // Calculate scaled versions of the bounds of mHitRegion and mMaybeHitRegion
+  // for quick access in FindPaintedLayerFor().
+  mScaledHitRegionBounds = aState->ScaleToOutsidePixels(mHitRegion.GetBounds());
+  mScaledMaybeHitRegionBounds = aState->ScaleToOutsidePixels(mMaybeHitRegion.GetBounds());
+}
+
+PaintedLayerData
+ContainerState::NewPaintedLayerData(nsDisplayItem* aItem,
+                                    AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                    const DisplayItemScrollClip* aScrollClip,
+                                    const nsPoint& aTopLeft,
+                                    bool aShouldFixToViewport)
+{
+  PaintedLayerData data;
+  data.mAnimatedGeometryRoot = aAnimatedGeometryRoot;
+  data.mScrollClip = aScrollClip;
+  data.mAnimatedGeometryRootOffset = aTopLeft;
+  data.mReferenceFrame = aItem->ReferenceFrame();
+  data.mSingleItemFixedToViewport = aShouldFixToViewport;
+  data.mBackfaceHidden = aItem->Frame()->In3DContextAndBackfaceIsHidden();
+
+  data.mNewChildLayersIndex = mNewChildLayers.Length();
+  NewLayerEntry* newLayerEntry = mNewChildLayers.AppendElement();
+  newLayerEntry->mAnimatedGeometryRoot = aAnimatedGeometryRoot;
+  newLayerEntry->mScrollClip = aScrollClip;
+  // newLayerEntry->mOpaqueRegion is filled in later from
+  // paintedLayerData->mOpaqueRegion, if necessary.
+
+  // Allocate another entry for this layer's optimization to ColorLayer/ImageLayer
+  mNewChildLayers.AppendElement();
+
+  return data;
+}
+
+#ifdef MOZ_DUMP_PAINTING
+static void
+DumpPaintedImage(nsDisplayItem* aItem, SourceSurface* aSurface)
+{
+  nsCString string(aItem->Name());
+  string.Append('-');
+  string.AppendInt((uint64_t)aItem);
+  fprintf_stderr(gfxUtils::sDumpPaintFile, "<script>array[\"%s\"]=\"", string.BeginReading());
+  gfxUtils::DumpAsDataURI(aSurface, gfxUtils::sDumpPaintFile);
+  fprintf_stderr(gfxUtils::sDumpPaintFile, "\";</script>\n");
+}
+#endif
+
+static void
+PaintInactiveLayer(nsDisplayListBuilder* aBuilder,
+                   LayerManager* aManager,
+                   nsDisplayItem* aItem,
+                   gfxContext* aContext,
+                   nsRenderingContext* aCtx)
+{
+  // This item has an inactive layer. Render it to a PaintedLayer
+  // using a temporary BasicLayerManager.
+  BasicLayerManager* basic = static_cast<BasicLayerManager*>(aManager);
+  RefPtr<gfxContext> context = aContext;
+#ifdef MOZ_DUMP_PAINTING
+  int32_t appUnitsPerDevPixel = AppUnitsPerDevPixel(aItem);
+  nsIntRect itemVisibleRect =
+    aItem->GetVisibleRect().ToOutsidePixels(appUnitsPerDevPixel);
+
+  RefPtr<DrawTarget> tempDT;
+  if (gfxEnv::DumpPaint()) {
+    tempDT = gfxPlatform::GetPlatform()->CreateOffscreenContentDrawTarget(
+                                      itemVisibleRect.Size(),
+                                      SurfaceFormat::B8G8R8A8);
+    if (tempDT) {
+      context = gfxContext::CreateOrNull(tempDT);
+      if (!context) {
+        // Leave this as crash, it's in the debugging code, we want to know
+        gfxDevCrash(LogReason::InvalidContext) << "PaintInactive context problem " << gfx::hexa(tempDT);
+        return;
+      }
+      context->SetMatrix(gfxMatrix::Translation(-itemVisibleRect.x,
+                                                -itemVisibleRect.y));
+    }
+  }
+#endif
+  basic->BeginTransaction();
+  basic->SetTarget(context);
+
+  if (aItem->GetType() == nsDisplayItem::TYPE_MASK) {
+    static_cast<nsDisplayMask*>(aItem)->PaintAsLayer(aBuilder, aCtx, basic);
+    if (basic->InTransaction()) {
+      basic->AbortTransaction();
+    }
+  } else if (aItem->GetType() == nsDisplayItem::TYPE_FILTER){
+    static_cast<nsDisplayFilter*>(aItem)->PaintAsLayer(aBuilder, aCtx, basic);
+    if (basic->InTransaction()) {
+      basic->AbortTransaction();
+    }
+  } else {
+    basic->EndTransaction(FrameLayerBuilder::DrawPaintedLayer, aBuilder);
+  }
+  FrameLayerBuilder *builder = static_cast<FrameLayerBuilder*>(basic->GetUserData(&gLayerManagerLayerBuilder));
+  if (builder) {
+    builder->DidEndTransaction();
+  }
+
+  basic->SetTarget(nullptr);
+
+#ifdef MOZ_DUMP_PAINTING
+  if (gfxEnv::DumpPaint() && tempDT) {
+    RefPtr<SourceSurface> surface = tempDT->Snapshot();
+    DumpPaintedImage(aItem, surface);
+
+    DrawTarget* drawTarget = aContext->GetDrawTarget();
+    Rect rect(itemVisibleRect.x, itemVisibleRect.y,
+              itemVisibleRect.width, itemVisibleRect.height);
+    drawTarget->DrawSurface(surface, rect, Rect(Point(0,0), rect.Size()));
+
+    aItem->SetPainted();
+  }
+#endif
+}
+
+/**
+ * Chooses a single active scrolled root for the entire display list, used
+ * when we are flattening layers.
+ */
+bool
+ContainerState::ChooseAnimatedGeometryRoot(const nsDisplayList& aList,
+                                           AnimatedGeometryRoot **aAnimatedGeometryRoot)
+{
+  for (nsDisplayItem* item = aList.GetBottom(); item; item = item->GetAbove()) {
+    LayerState layerState = item->GetLayerState(mBuilder, mManager, mParameters);
+    // Don't use an item that won't be part of any PaintedLayers to pick the
+    // active scrolled root.
+    if (layerState == LAYER_ACTIVE_FORCE) {
+      continue;
+    }
+
+    // Try using the actual active scrolled root of the backmost item, as that
+    // should result in the least invalidation when scrolling.
+    *aAnimatedGeometryRoot = item->GetAnimatedGeometryRoot();
+    return true;
+  }
+  return false;
+}
+
+nsIntRegion
+ContainerState::ComputeOpaqueRect(nsDisplayItem* aItem,
+                                  AnimatedGeometryRoot* aAnimatedGeometryRoot,
+                                  const DisplayItemClip& aClip,
+                                  nsDisplayList* aList,
+                                  bool* aHideAllLayersBelow,
+                                  bool* aOpaqueForAnimatedGeometryRootParent)
+{
+  bool snapOpaque;
+  nsRegion opaque = aItem->GetOpaqueRegion(mBuilder, &snapOpaque);
+  if (opaque.IsEmpty()) {
+    return nsIntRegion();
+  }
+
+  nsIntRegion opaquePixels;
+  nsRegion opaqueClipped;
+  for (auto iter = opaque.RectIter(); !iter.Done(); iter.Next()) {
+    opaqueClipped.Or(opaqueClipped,
+                     aClip.ApproximateIntersectInward(iter.Get()));
+  }
+  if (aAnimatedGeometryRoot == mContainerAnimatedGeometryRoot &&
+      opaqueClipped.Contains(mContainerBounds)) {
+    *aHideAllLayersBelow = true;
+    aList->SetIsOpaque();
+  }
+  // Add opaque areas to the "exclude glass" region. Only do this when our
+  // container layer is going to be the rootmost layer, otherwise transforms
+  // etc will mess us up (and opaque contributions from other containers are
+  // not needed).
+  if (!nsLayoutUtils::GetCrossDocParentFrame(mContainerFrame)) {
+    mBuilder->AddWindowOpaqueRegion(opaqueClipped);
+  }
+  opaquePixels = ScaleRegionToInsidePixels(opaqueClipped, snapOpaque);
+
+  if (IsInInactiveLayer()) {
+    return opaquePixels;
+  }
+
+  nsIScrollableFrame* sf = nsLayoutUtils::GetScrollableFrameFor(*aAnimatedGeometryRoot);
+  if (sf) {
+    nsRect displayport;
+    bool usingDisplayport =
+      nsLayoutUtils::GetDisplayPort((*aAnimatedGeometryRoot)->GetContent(), &displayport,
+        RelativeTo::ScrollFrame);
+    if (!usingDisplayport) {
+      // No async scrolling, so all that matters is that the layer contents
+      // cover the scrollport.
+      displayport = sf->GetScrollPortRect();
+    }
+    nsIFrame* scrollFrame = do_QueryFrame(sf);
+    displayport += scrollFrame->GetOffsetToCrossDoc(mContainerReferenceFrame);
+    if (opaquePixels.Contains(ScaleRegionToNearestPixels(displayport))) {
+      *aOpaqueForAnimatedGeometryRootParent = true;
+    }
+  }
+  return opaquePixels;
+}
+
+static const DisplayItemScrollClip*
+InnermostScrollClipApplicableToAGR(const DisplayItemScrollClip* aItemScrollClip,
+                                   AnimatedGeometryRoot* aAnimatedGeometryRoot)
+{
+  // "Applicable" scroll clips are those that are for nsIScrollableFrames
+  // that are ancestors of aAnimatedGeometryRoot or ancestors of aContainerScrollClip.
+  // They can be applied to all items sharing this animated geometry root, so
+  // instead of applying to the items individually, they can be applied to the
+  // whole layer.
+  for (const DisplayItemScrollClip* scrollClip = aItemScrollClip;
+       scrollClip;
+       scrollClip = scrollClip->mParent) {
+    nsIFrame* scrolledFrame = scrollClip->mScrollableFrame->GetScrolledFrame();
+    if (nsLayoutUtils::IsAncestorFrameCrossDoc(scrolledFrame, *aAnimatedGeometryRoot)) {
+      // scrollClip and all its ancestors are applicable.
+      return scrollClip;
+    }
+  }
+  return nullptr;
+}
+
+Maybe<size_t>
+ContainerState::SetupMaskLayerForScrolledClip(Layer* aLayer,
+                                              const DisplayItemClip& aClip)
+{
+  if (aClip.GetRoundedRectCount() > 0) {
+    Maybe<size_t> maskLayerIndex = Some(aLayer->GetAncestorMaskLayerCount());
+    if (RefPtr<Layer> maskLayer = CreateMaskLayer(aLayer, aClip, maskLayerIndex,
+                                                  aClip.GetRoundedRectCount())) {
+      aLayer->AddAncestorMaskLayer(maskLayer);
+      return maskLayerIndex;
+    }
+    // Fall through to |return Nothing()|.
+  }
+  return Nothing();
+}
+
+void
+ContainerState::SetupMaskLayerForCSSMask(Layer* aLayer,
+                                         nsDisplayMask* aMaskItem)
+{
+  MOZ_ASSERT(mManager->IsCompositingCheap());
+
+  RefPtr<ImageLayer> maskLayer =
+    CreateOrRecycleMaskImageLayerFor(MaskLayerKey(aLayer, Nothing()),
+      [](Layer* aMaskLayer)
+      {
+        aMaskLayer->SetUserData(&gCSSMaskLayerUserData,
+                                new CSSMaskLayerUserData());
+      }
+    );
+
+  CSSMaskLayerUserData* oldUserData =
+    static_cast<CSSMaskLayerUserData*>(maskLayer->GetUserData(&gCSSMaskLayerUserData));
+
+  bool snap;
+  nsRect bounds = aMaskItem->GetBounds(mBuilder, &snap);
+  nsIntRect itemRect = ScaleToOutsidePixels(bounds, snap);
+  CSSMaskLayerUserData newUserData(aMaskItem->Frame(), itemRect);
+  if (*oldUserData == newUserData) {
+    aLayer->SetMaskLayer(maskLayer);
+    return;
+  }
+
+  int32_t maxSize = mManager->GetMaxTextureSize();
+  IntSize surfaceSize(std::min(itemRect.width, maxSize),
+                      std::min(itemRect.height, maxSize));
+
+  if (surfaceSize.IsEmpty()) {
+    // Return early if we know that the size of this mask surface is empty.
+    return;
+  }
+
+  MaskImageData imageData(surfaceSize, mManager);
+  RefPtr<DrawTarget> dt = imageData.CreateDrawTarget();
+  if (!dt || !dt->IsValid()) {
+    NS_WARNING("Could not create DrawTarget for mask layer.");
+    return;
+  }
+
+  RefPtr<gfxContext> maskCtx = gfxContext::CreateOrNull(dt);
+  maskCtx->SetMatrix(gfxMatrix::Translation(-itemRect.TopLeft()));
+  maskCtx->Multiply(gfxMatrix::Scaling(mParameters.mXScale, mParameters.mYScale));
+
+  if (!aMaskItem->PaintMask(mBuilder, maskCtx)) {
+    // Mostly because of mask resource is not ready.
+    return;
+  }
+
+  // Setup mask layer offset.
+  Matrix4x4 matrix;
+  matrix.PreTranslate(itemRect.x, itemRect.y, 0);
+  matrix.PreTranslate(mParameters.mOffset.x, mParameters.mOffset.y, 0);
+
+  maskLayer->SetBaseTransform(matrix);
+
+  RefPtr<ImageContainer> imgContainer =
+    imageData.CreateImageAndImageContainer();
+  if (!imgContainer) {
+    return;
+  }
+  maskLayer->SetContainer(imgContainer);
+
+  *oldUserData = newUserData;
+  aLayer->SetMaskLayer(maskLayer);
+}
+
+/*
+ * Iterate through the non-clip items in aList and its descendants.
+ * For each item we compute the effective clip rect. Each item is assigned
+ * to a layer. We invalidate the areas in PaintedLayers where an item
+ * has moved from one PaintedLayer to another. Also,
+ * aState->mInvalidPaintedContent is invalidated in every PaintedLayer.
+ * We set the clip rect for items that generated their own layer, and
+ * create a mask layer to do any rounded rect clipping.
+ * (PaintedLayers don't need a clip rect on the layer, we clip the items
+ * individually when we draw them.)
+ * We set the visible rect for all layers, although the actual setting
+ * of visible rects for some PaintedLayers is deferred until the calling
+ * of ContainerState::Finish.
+ */
+void
+ContainerState::ProcessDisplayItems(nsDisplayList* aList)
+{
+  PROFILER_LABEL("ContainerState", "ProcessDisplayItems",
+    js::ProfileEntry::Category::GRAPHICS);
+
+  AnimatedGeometryRoot* lastAnimatedGeometryRoot = mContainerAnimatedGeometryRoot;
+  nsPoint lastAGRTopLeft;
+  nsPoint topLeft(0,0);
+
+  // When NO_COMPONENT_ALPHA is set, items will be flattened into a single
+  // layer, so we need to choose which active scrolled root to use for all
+  // items.
+  if (mFlattenToSingleLayer) {
+    if (ChooseAnimatedGeometryRoot(*aList, &lastAnimatedGeometryRoot)) {
+      lastAGRTopLeft = (*lastAnimatedGeometryRoot)->GetOffsetToCrossDoc(mContainerReferenceFrame);
+    }
+  }
+
+  int32_t maxLayers = gfxPrefs::MaxActiveLayers();
+  int layerCount = 0;
+
+  nsDisplayList savedItems;
+  nsDisplayItem* item;
+  while ((item = aList->RemoveBottom()) != nullptr) {
+    nsDisplayItem::Type itemType = item->GetType();
+
+    // If the item is a event regions item, but is empty (has no regions in it)
+    // then we should just throw it out
+    if (itemType == nsDisplayItem::TYPE_LAYER_EVENT_REGIONS) {
+      nsDisplayLayerEventRegions* eventRegions =
+        static_cast<nsDisplayLayerEventRegions*>(item);
+      if (eventRegions->IsEmpty()) {
+        item->~nsDisplayItem();
+        continue;
+      }
+    }
+
+    // Peek ahead to the next item and try merging with it or swapping with it
+    // if necessary.
+    nsDisplayItem* aboveItem;
+    while ((aboveItem = aList->GetBottom()) != nullptr) {
+      if (aboveItem->TryMerge(item)) {
+        aList->RemoveBottom();
+        item->~nsDisplayItem();
+        item = aboveItem;
+        itemType = item->GetType();
+      } else {
+        break;
+      }
+    }
+
+    nsDisplayList* itemSameCoordinateSystemChildren
+      = item->GetSameCoordinateSystemChildren();
+    if (item->ShouldFlattenAway(mBuilder)) {
+      aList->AppendToBottom(itemSameCoordinateSystemChildren);
+      item->~nsDisplayItem();
+      continue;
+    }
+
+    savedItems.AppendToTop(item);
+
+    NS_ASSERTION(mAppUnitsPerDevPixel == AppUnitsPerDevPixel(item),
+      "items in a container layer should all have the same app units per dev pixel");
+
+    if (mBuilder->NeedToForceTransparentSurfaceForItem(item)) {
+      aList->SetNeedsTransparentSurface();
+    }
+
+    if (mParameters.mForEventsAndPluginsOnly && !item->GetChildren() &&
+        (itemType != nsDisplayItem::TYPE_LAYER_EVENT_REGIONS &&
+         itemType != nsDisplayItem::TYPE_PLUGIN)) {
+      continue;
+    }
+
+    LayerState layerState = item->GetLayerState(mBuilder, mManager, mParameters);
+    if (layerState == LAYER_INACTIVE &&
+        nsDisplayItem::ForceActiveLayers()) {
+      layerState = LAYER_ACTIVE;
+    }
+
+    bool forceInactive;
+    AnimatedGeometryRoot* animatedGeometryRoot;
+    AnimatedGeometryRoot* animatedGeometryRootForClip = nullptr;
+    if (mFlattenToSingleLayer && layerState != LAYER_ACTIVE_FORCE) {
+      forceInactive = true;
+      animatedGeometryRoot = lastAnimatedGeometryRoot;
+      topLeft = lastAGRTopLeft;
+    } else {
+      forceInactive = false;
+      if (mManager->IsWidgetLayerManager()) {
+        animatedGeometryRoot = item->GetAnimatedGeometryRoot();
+        animatedGeometryRootForClip = item->AnimatedGeometryRootForScrollMetadata();
+      } else {
+        // For inactive layer subtrees, splitting content into PaintedLayers
+        // based on animated geometry roots is pointless. It's more efficient
+        // to build the minimum number of layers.
+        animatedGeometryRoot = mContainerAnimatedGeometryRoot;
+
+      }
+      topLeft = (*animatedGeometryRoot)->GetOffsetToCrossDoc(mContainerReferenceFrame);
+    }
+    if (!animatedGeometryRootForClip) {
+      animatedGeometryRootForClip = animatedGeometryRoot;
+    }
+
+    const DisplayItemScrollClip* itemScrollClip = item->ScrollClip();
+    // Now we need to separate the item's scroll clip chain into those scroll
+    // clips that can  be applied to the whole layer (i.e. to all items
+    // sharing the item's animated geometry root), and those that need to be
+    // applied to the item itself.
+    const DisplayItemScrollClip* agrScrollClip =
+      InnermostScrollClipApplicableToAGR(itemScrollClip, animatedGeometryRootForClip);
+    MOZ_ASSERT(DisplayItemScrollClip::IsAncestor(agrScrollClip, itemScrollClip));
+
+    if (agrScrollClip != itemScrollClip) {
+      // Pick up any scroll clips that should apply to the item and apply them.
+      DisplayItemClip clip = item->GetClip();
+      for (const DisplayItemScrollClip* scrollClip = itemScrollClip;
+           scrollClip && scrollClip != agrScrollClip && scrollClip != mContainerScrollClip;
+           scrollClip = scrollClip->mParent) {
+        if (scrollClip->mClip) {
+          clip.IntersectWith(*scrollClip->mClip);
+        }
+      }
+      item->SetClip(mBuilder, clip);
+    }
+
+    bool clipMovesWithLayer = (animatedGeometryRoot == animatedGeometryRootForClip);
+
+    bool shouldFixToViewport = !clipMovesWithLayer &&
+        !(*animatedGeometryRoot)->GetParent() &&
+        item->ShouldFixToViewport(mBuilder);
+
+    // For items that are fixed to the viewport, remove their clip at the
+    // display item level because additional areas could be brought into
+    // view by async scrolling. Save the clip so we can set it on the layer
+    // instead later.
+    DisplayItemClip fixedToViewportClip = DisplayItemClip::NoClip();
+    if (shouldFixToViewport) {
+      fixedToViewportClip = item->GetClip();
+      item->SetClip(mBuilder, DisplayItemClip::NoClip());
+    }
+
+    bool snap;
+    nsRect itemContent = item->GetBounds(mBuilder, &snap);
+    if (itemType == nsDisplayItem::TYPE_LAYER_EVENT_REGIONS) {
+      nsDisplayLayerEventRegions* eventRegions =
+        static_cast<nsDisplayLayerEventRegions*>(item);
+      itemContent = eventRegions->GetHitRegionBounds(mBuilder, &snap);
+    }
+    nsIntRect itemDrawRect = ScaleToOutsidePixels(itemContent, snap);
+    bool prerenderedTransform = itemType == nsDisplayItem::TYPE_TRANSFORM &&
+        static_cast<nsDisplayTransform*>(item)->MayBeAnimated(mBuilder);
+    ParentLayerIntRect clipRect;
+    const DisplayItemClip& itemClip = item->GetClip();
+    if (itemClip.HasClip()) {
+      itemContent.IntersectRect(itemContent, itemClip.GetClipRect());
+      clipRect = ViewAs<ParentLayerPixel>(ScaleToNearestPixels(itemClip.GetClipRect()));
+      if (!prerenderedTransform) {
+        itemDrawRect.IntersectRect(itemDrawRect, clipRect.ToUnknownRect());
+      }
+      clipRect.MoveBy(ViewAs<ParentLayerPixel>(mParameters.mOffset));
+    }
+#ifdef DEBUG
+    nsRect bounds = itemContent;
+    bool dummy;
+    if (itemType == nsDisplayItem::TYPE_LAYER_EVENT_REGIONS) {
+      bounds = item->GetBounds(mBuilder, &dummy);
+      if (itemClip.HasClip()) {
+        bounds.IntersectRect(bounds, itemClip.GetClipRect());
+      }
+    }
+    bounds = fixedToViewportClip.ApplyNonRoundedIntersection(bounds);
+    if (!bounds.IsEmpty()) {
+      for (const DisplayItemScrollClip* scrollClip = itemScrollClip;
+           scrollClip && scrollClip != mContainerScrollClip;
+           scrollClip = scrollClip->mParent) {
+        if (scrollClip->mClip) {
+          if (scrollClip->mIsAsyncScrollable) {
+            bounds = scrollClip->mClip->GetClipRect();
+          } else {
+            bounds = scrollClip->mClip->ApplyNonRoundedIntersection(bounds);
+          }
+        }
+      }
+    }
+    ((nsRect&)mAccumulatedChildBounds).UnionRect(mAccumulatedChildBounds, bounds);
+#endif
+
+    nsIntRect itemVisibleRect = itemDrawRect;
+    // We haven't computed visibility at this point, so item->GetVisibleRect()
+    // is just the dirty rect that item was initialized with. We intersect it
+    // with the clipped item bounds to get a tighter visible rect.
+    itemVisibleRect = itemVisibleRect.Intersect(
+      ScaleToOutsidePixels(item->GetVisibleRect(), false));
+
+    if (maxLayers != -1 && layerCount >= maxLayers) {
+      forceInactive = true;
+    }
+
+    // Assign the item to a layer
+    if (layerState == LAYER_ACTIVE_FORCE ||
+        (layerState == LAYER_INACTIVE && !mManager->IsWidgetLayerManager()) ||
+        (!forceInactive &&
+         (layerState == LAYER_ACTIVE_EMPTY ||
+          layerState == LAYER_ACTIVE))) {
+
+      layerCount++;
+
+      // LAYER_ACTIVE_EMPTY means the layer is created just for its metadata.
+      // We should never see an empty layer with any visible content!
+      NS_ASSERTION(layerState != LAYER_ACTIVE_EMPTY ||
+                   itemVisibleRect.IsEmpty(),
+                   "State is LAYER_ACTIVE_EMPTY but visible rect is not.");
+
+      // As long as the new layer isn't going to be a PaintedLayer,
+      // InvalidateForLayerChange doesn't need the new layer pointer.
+      // We also need to check the old data now, because BuildLayer
+      // can overwrite it.
+      InvalidateForLayerChange(item, nullptr);
+
+      // If the item would have its own layer but is invisible, just hide it.
+      // Note that items without their own layers can't be skipped this
+      // way, since their PaintedLayer may decide it wants to draw them
+      // into its buffer even if they're currently covered.
+      if (itemVisibleRect.IsEmpty() &&
+          !item->ShouldBuildLayerEvenIfInvisible(mBuilder)) {
+        continue;
+      }
+
+      if (mScrollClipForPerspectiveChild) {
+        // We are the single transform child item of an nsDisplayPerspective.
+        // Our parent forwarded a scroll clip to us. Pick it up.
+        // We do this after any clipping has been applied, because this
+        // forwarded scroll clip is only used for scrolling (in the form of
+        // APZ frame metrics), not for clipping - the clip still belongs on
+        // the perspective item.
+        MOZ_ASSERT(itemType == nsDisplayItem::TYPE_TRANSFORM);
+        MOZ_ASSERT(!itemScrollClip);
+        MOZ_ASSERT(!agrScrollClip);
+        MOZ_ASSERT(DisplayItemScrollClip::IsAncestor(mContainerScrollClip,
+                                                      mScrollClipForPerspectiveChild));
+        itemScrollClip = mScrollClipForPerspectiveChild;
+        agrScrollClip = mScrollClipForPerspectiveChild;
+      }
+
+      // 3D-transformed layers don't necessarily draw in the order in which
+      // they're added to their parent container layer.
+      bool mayDrawOutOfOrder = itemType == nsDisplayItem::TYPE_TRANSFORM &&
+        (item->Frame()->Combines3DTransformWithAncestors() ||
+         item->Frame()->Extend3DContext());
+
+      // Let mPaintedLayerDataTree know about this item, so that
+      // FindPaintedLayerFor and FindOpaqueBackgroundColor are aware of this
+      // item, even though it's not in any PaintedLayerDataStack.
+      // Ideally we'd only need the "else" case here and have
+      // mPaintedLayerDataTree figure out the right clip from the animated
+      // geometry root that we give it, but it can't easily figure about
+      // overflow:hidden clips on ancestors just by looking at the frame.
+      // So we'll do a little hand holding and pass the clip instead of the
+      // visible rect for the two important cases.
+      nscolor uniformColor = NS_RGBA(0,0,0,0);
+      nscolor* uniformColorPtr = (mayDrawOutOfOrder || IsInInactiveLayer()) ? nullptr :
+                                                                              &uniformColor;
+      nsIntRect clipRectUntyped;
+      const DisplayItemClip& layerClip = shouldFixToViewport ? fixedToViewportClip : itemClip;
+      ParentLayerIntRect layerClipRect;
+      nsIntRect* clipPtr = nullptr;
+      if (layerClip.HasClip()) {
+        layerClipRect = ViewAs<ParentLayerPixel>(
+          ScaleToNearestPixels(layerClip.GetClipRect()) + mParameters.mOffset);
+        clipRectUntyped = layerClipRect.ToUnknownRect();
+        clipPtr = &clipRectUntyped;
+      }
+      if (*animatedGeometryRoot == item->Frame() &&
+          *animatedGeometryRoot != mBuilder->RootReferenceFrame()) {
+        // This is the case for scrollbar thumbs, for example. In that case the
+        // clip we care about is the overflow:hidden clip on the scrollbar.
+        mPaintedLayerDataTree.AddingOwnLayer(animatedGeometryRoot->mParentAGR,
+                                             clipPtr,
+                                             uniformColorPtr);
+      } else if (prerenderedTransform) {
+        mPaintedLayerDataTree.AddingOwnLayer(animatedGeometryRoot,
+                                             clipPtr,
+                                             uniformColorPtr);
+      } else if (shouldFixToViewport) {
+        mPaintedLayerDataTree.AddingOwnLayer(animatedGeometryRootForClip,
+                                             clipPtr,
+                                             uniformColorPtr);
+      } else {
+        // Using itemVisibleRect here isn't perfect. itemVisibleRect can be
+        // larger or smaller than the potential bounds of item's contents in
+        // animatedGeometryRoot: It's too large if there's a clipped display
+        // port somewhere among item's contents (see bug 1147673), and it can
+        // be too small if the contents can move, because it only looks at the
+        // contents' current bounds and doesn't anticipate any animations.
+        // Time will tell whether this is good enough, or whether we need to do
+        // something more sophisticated here.
+        mPaintedLayerDataTree.AddingOwnLayer(animatedGeometryRoot,
+                                             &itemVisibleRect, uniformColorPtr);
+      }
+
+      ContainerLayerParameters params = mParameters;
+      params.mBackgroundColor = uniformColor;
+      params.mLayerCreationHint = GetLayerCreationHint(animatedGeometryRoot);
+      params.mScrollClip = agrScrollClip;
+      params.mScrollClipForPerspectiveChild = nullptr;
+
+      if (itemType == nsDisplayItem::TYPE_PERSPECTIVE) {
+        // Perspective items have a single child item, an nsDisplayTransform.
+        // If the perspective item is scrolled, but the perspective-inducing
+        // frame is outside the scroll frame (indicated by this items AGR
+        // being outside that scroll frame), we have to take special care to
+        // make APZ scrolling work properly. APZ needs us to put the scroll
+        // frame's FrameMetrics on our child transform ContainerLayer instead.
+        // Our agrScrollClip is the scroll clip that's applicable to our
+        // perspective frame, so it won't be the scroll clip for the scrolled
+        // frame in the case that we care about, and we'll forward that scroll
+        // clip to our child.
+        params.mScrollClipForPerspectiveChild = itemScrollClip;
+      }
+
+      // Just use its layer.
+      // Set layerContentsVisibleRect.width/height to -1 to indicate we
+      // currently don't know. If BuildContainerLayerFor gets called by
+      // item->BuildLayer, this will be set to a proper rect.
+      nsIntRect layerContentsVisibleRect(0, 0, -1, -1);
+      params.mLayerContentsVisibleRect = &layerContentsVisibleRect;
+      RefPtr<Layer> ownLayer = item->BuildLayer(mBuilder, mManager, params);
+      if (!ownLayer) {
+        continue;
+      }
+
+      NS_ASSERTION(!ownLayer->AsPaintedLayer(),
+                   "Should never have created a dedicated Painted layer!");
+
+      if (item->BackfaceIsHidden()) {
+        ownLayer->SetContentFlags(ownLayer->GetContentFlags() |
+                                  Layer::CONTENT_BACKFACE_HIDDEN);
+      } else {
+        ownLayer->SetContentFlags(ownLayer->GetContentFlags() &
+                                  ~Layer::CONTENT_BACKFACE_HIDDEN);
+      }
+
+      nsRect invalid;
+      if (item->IsInvalid(invalid)) {
+        ownLayer->SetInvalidRectToVisibleRegion();
+      }
+
+      // If it's not a ContainerLayer, we need to apply the scale transform
+      // ourselves.
+      if (!ownLayer->AsContainerLayer()) {
+        ownLayer->SetPostScale(mParameters.mXScale,
+                               mParameters.mYScale);
+      }
+
+      // Update that layer's clip and visible rects.
+      NS_ASSERTION(ownLayer->Manager() == mManager, "Wrong manager");
+      NS_ASSERTION(!ownLayer->HasUserData(&gLayerManagerUserData),
+                   "We shouldn't have a FrameLayerBuilder-managed layer here!");
+      NS_ASSERTION(layerClip.HasClip() ||
+                   layerClip.GetRoundedRectCount() == 0,
+                   "If we have rounded rects, we must have a clip rect");
+
+      // It has its own layer. Update that layer's clip and visible rects.
+
+      ownLayer->SetClipRect(Nothing());
+      ownLayer->SetScrolledClip(Nothing());
+      if (layerClip.HasClip()) {
+        // For layers fixed to the viewport, the clip becomes part of the
+        // layer's scrolled clip. Otherwise, it becomes part of the layer clip.
+        if (shouldFixToViewport) {
+          LayerClip scrolledClip;
+          scrolledClip.SetClipRect(layerClipRect);
+          if (layerClip.GetRoundedRectCount() > 0) {
+            scrolledClip.SetMaskLayerIndex(
+                SetupMaskLayerForScrolledClip(ownLayer.get(), layerClip));
+          }
+          ownLayer->SetScrolledClip(Some(scrolledClip));
+        } else {
+          ownLayer->SetClipRect(Some(layerClipRect));
+
+          // rounded rectangle clipping using mask layers
+          // (must be done after visible rect is set on layer)
+          if (layerClip.GetRoundedRectCount() > 0) {
+            SetupMaskLayer(ownLayer, layerClip);
+          }
+        }
+      } else if (item->GetType() == nsDisplayItem::TYPE_MASK) {
+        nsDisplayMask* maskItem = static_cast<nsDisplayMask*>(item);
+        SetupMaskLayerForCSSMask(ownLayer, maskItem);
+      }
+
+      ContainerLayer* oldContainer = ownLayer->GetParent();
+      if (oldContainer && oldContainer != mContainerLayer) {
+        oldContainer->RemoveChild(ownLayer);
+      }
+      NS_ASSERTION(FindIndexOfLayerIn(mNewChildLayers, ownLayer) < 0,
+                   "Layer already in list???");
+
+      NewLayerEntry* newLayerEntry = mNewChildLayers.AppendElement();
+      newLayerEntry->mLayer = ownLayer;
+      newLayerEntry->mAnimatedGeometryRoot = animatedGeometryRoot;
+      newLayerEntry->mScrollClip = agrScrollClip;
+      newLayerEntry->mLayerState = layerState;
+
+      // Don't attempt to flatten compnent alpha layers that are within
+      // a forced active layer, or an active transform;
+      if (itemType == nsDisplayItem::TYPE_TRANSFORM ||
+          layerState == LAYER_ACTIVE_FORCE) {
+        newLayerEntry->mPropagateComponentAlphaFlattening = false;
+      }
+      // nsDisplayTransform::BuildLayer must set layerContentsVisibleRect.
+      // We rely on this to ensure 3D transforms compute a reasonable
+      // layer visible region.
+      NS_ASSERTION(itemType != nsDisplayItem::TYPE_TRANSFORM ||
+                   layerContentsVisibleRect.width >= 0,
+                   "Transform items must set layerContentsVisibleRect!");
+      if (mLayerBuilder->IsBuildingRetainedLayers()) {
+        newLayerEntry->mLayerContentsVisibleRect = layerContentsVisibleRect;
+        if (itemType == nsDisplayItem::TYPE_PERSPECTIVE ||
+            (itemType == nsDisplayItem::TYPE_TRANSFORM &&
+             (item->Frame()->Extend3DContext() ||
+              item->Frame()->Combines3DTransformWithAncestors() ||
+              item->Frame()->HasPerspective()))) {
+          // Give untransformed visible region as outer visible region
+          // to avoid failure caused by singular transforms.
+          newLayerEntry->mUntransformedVisibleRegion = true;
+          newLayerEntry->mVisibleRegion =
+            item->GetVisibleRectForChildren().ToOutsidePixels(mAppUnitsPerDevPixel);
+        } else {
+          newLayerEntry->mVisibleRegion = itemVisibleRect;
+        }
+        newLayerEntry->mOpaqueRegion = ComputeOpaqueRect(item,
+          animatedGeometryRoot, layerClip, aList,
+          &newLayerEntry->mHideAllLayersBelow,
+          &newLayerEntry->mOpaqueForAnimatedGeometryRootParent);
+      } else {
+        bool useChildrenVisible =
+          itemType == nsDisplayItem::TYPE_TRANSFORM &&
+          (item->Frame()->IsPreserve3DLeaf() ||
+           item->Frame()->HasPerspective());
+        const nsIntRegion &visible = useChildrenVisible ?
+          item->GetVisibleRectForChildren().ToOutsidePixels(mAppUnitsPerDevPixel):
+          itemVisibleRect;
+
+        SetOuterVisibleRegionForLayer(ownLayer, visible,
+            layerContentsVisibleRect.width >= 0 ? &layerContentsVisibleRect : nullptr,
+            useChildrenVisible);
+      }
+      if (itemType == nsDisplayItem::TYPE_SCROLL_INFO_LAYER) {
+        nsDisplayScrollInfoLayer* scrollItem = static_cast<nsDisplayScrollInfoLayer*>(item);
+        newLayerEntry->mOpaqueForAnimatedGeometryRootParent = false;
+        newLayerEntry->mBaseScrollMetadata =
+            scrollItem->ComputeScrollMetadata(ownLayer, mParameters);
+      } else if ((itemType == nsDisplayItem::TYPE_SUBDOCUMENT ||
+                  itemType == nsDisplayItem::TYPE_ZOOM ||
+                  itemType == nsDisplayItem::TYPE_RESOLUTION) &&
+                 gfxPrefs::LayoutUseContainersForRootFrames())
+      {
+        newLayerEntry->mBaseScrollMetadata =
+          static_cast<nsDisplaySubDocument*>(item)->ComputeScrollMetadata(ownLayer, mParameters);
+      }
+
+      /**
+       * No need to allocate geometry for items that aren't
+       * part of a PaintedLayer.
+       */
+      mLayerBuilder->AddLayerDisplayItem(ownLayer, item, layerState, nullptr);
+    } else {
+      PaintedLayerData* paintedLayerData =
+        mPaintedLayerDataTree.FindPaintedLayerFor(animatedGeometryRoot, agrScrollClip,
+                                                  itemVisibleRect,
+                                                  item->Frame()->In3DContextAndBackfaceIsHidden(),
+                                                  [&]() {
+          return NewPaintedLayerData(item, animatedGeometryRoot, agrScrollClip,
+                                     topLeft, shouldFixToViewport);
+        });
+
+      if (itemType == nsDisplayItem::TYPE_LAYER_EVENT_REGIONS) {
+        nsDisplayLayerEventRegions* eventRegions =
+            static_cast<nsDisplayLayerEventRegions*>(item);
+        paintedLayerData->AccumulateEventRegions(this, eventRegions);
+      } else {
+        // check to see if the new item has rounded rect clips in common with
+        // other items in the layer
+        if (mManager->IsWidgetLayerManager()) {
+          paintedLayerData->UpdateCommonClipCount(itemClip);
+        }
+        nsIntRegion opaquePixels = ComputeOpaqueRect(item,
+            animatedGeometryRoot, itemClip, aList,
+            &paintedLayerData->mHideAllLayersBelow,
+            &paintedLayerData->mOpaqueForAnimatedGeometryRootParent);
+        MOZ_ASSERT(nsIntRegion(itemDrawRect).Contains(opaquePixels));
+        opaquePixels.AndWith(itemVisibleRect);
+        paintedLayerData->Accumulate(this, item, opaquePixels,
+            itemVisibleRect, itemClip, layerState);
+
+        // If we removed the clip from the display item above because it's
+        // fixed to the viewport, save it on the PaintedLayerData so we can
+        // set it on the layer later.
+        if (fixedToViewportClip.HasClip()) {
+          paintedLayerData->mItemClip = fixedToViewportClip;
+        }
+
+        if (!paintedLayerData->mLayer) {
+          // Try to recycle the old layer of this display item.
+          RefPtr<PaintedLayer> layer =
+            AttemptToRecyclePaintedLayer(animatedGeometryRoot, item, topLeft);
+          if (layer) {
+            paintedLayerData->mLayer = layer;
+
+            NS_ASSERTION(FindIndexOfLayerIn(mNewChildLayers, layer) < 0,
+                         "Layer already in list???");
+            mNewChildLayers[paintedLayerData->mNewChildLayersIndex].mLayer = layer.forget();
+          }
+        }
+      }
+    }
+
+    if (itemSameCoordinateSystemChildren &&
+        itemSameCoordinateSystemChildren->NeedsTransparentSurface()) {
+      aList->SetNeedsTransparentSurface();
+    }
+  }
+
+  aList->AppendToTop(&savedItems);
+}
+
+void
+ContainerState::InvalidateForLayerChange(nsDisplayItem* aItem, PaintedLayer* aNewLayer)
+{
+  NS_ASSERTION(aItem->GetPerFrameKey(),
+               "Display items that render using Thebes must have a key");
+  nsDisplayItemGeometry* oldGeometry = nullptr;
+  DisplayItemClip* oldClip = nullptr;
+  Layer* oldLayer = mLayerBuilder->GetOldLayerFor(aItem, &oldGeometry, &oldClip);
+  if (aNewLayer != oldLayer && oldLayer) {
+    // The item has changed layers.
+    // Invalidate the old bounds in the old layer and new bounds in the new layer.
+    PaintedLayer* t = oldLayer->AsPaintedLayer();
+    if (t && oldGeometry) {
+      // Note that whenever the layer's scale changes, we invalidate the whole thing,
+      // so it doesn't matter whether we are using the old scale at last paint
+      // or a new scale here
+#ifdef MOZ_DUMP_PAINTING
+      if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+        printf_stderr("Display item type %s(%p) changed layers %p to %p!\n", aItem->Name(), aItem->Frame(), t, aNewLayer);
+      }
+#endif
+      InvalidatePostTransformRegion(t,
+          oldGeometry->ComputeInvalidationRegion(),
+          *oldClip,
+          mLayerBuilder->GetLastPaintOffset(t));
+    }
+    // Clear the old geometry so that invalidation thinks the item has been
+    // added this paint.
+    mLayerBuilder->ClearCachedGeometry(aItem);
+    aItem->NotifyRenderingChanged();
+  }
+}
+
+void
+FrameLayerBuilder::ComputeGeometryChangeForItem(DisplayItemData* aData)
+{
+  nsDisplayItem *item = aData->mItem;
+  PaintedLayer* paintedLayer = aData->mLayer->AsPaintedLayer();
+  if (!item || !paintedLayer) {
+    aData->EndUpdate();
+    return;
+  }
+
+  PaintedLayerItemsEntry* entry = mPaintedLayerItems.GetEntry(paintedLayer);
+
+  nsAutoPtr<nsDisplayItemGeometry> geometry;
+
+  PaintedDisplayItemLayerUserData* layerData =
+    static_cast<PaintedDisplayItemLayerUserData*>(aData->mLayer->GetUserData(&gPaintedDisplayItemLayerUserData));
+  nsPoint shift = layerData->mAnimatedGeometryRootOrigin - layerData->mLastAnimatedGeometryRootOrigin;
+
+  const DisplayItemClip& clip = item->GetClip();
+
+  // If the frame is marked as invalidated, and didn't specify a rect to invalidate then we want to
+  // invalidate both the old and new bounds, otherwise we only want to invalidate the changed areas.
+  // If we do get an invalid rect, then we want to add this on top of the change areas.
+  nsRect invalid;
+  nsRegion combined;
+  bool notifyRenderingChanged = true;
+  if (!aData->mGeometry) {
+    // This item is being added for the first time, invalidate its entire area.
+    geometry = item->AllocateGeometry(mDisplayListBuilder);
+    combined = clip.ApplyNonRoundedIntersection(geometry->ComputeInvalidationRegion());
+#ifdef MOZ_DUMP_PAINTING
+    if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+      printf_stderr("Display item type %s(%p) added to layer %p!\n", item->Name(), item->Frame(), aData->mLayer.get());
+    }
+#endif
+  } else if (aData->mIsInvalid || (item->IsInvalid(invalid) && invalid.IsEmpty())) {
+    // Layout marked item/frame as needing repainting (without an explicit rect), invalidate the entire old and new areas.
+    geometry = item->AllocateGeometry(mDisplayListBuilder);
+    combined = aData->mClip.ApplyNonRoundedIntersection(aData->mGeometry->ComputeInvalidationRegion());
+    combined.MoveBy(shift);
+    combined.Or(combined, clip.ApplyNonRoundedIntersection(geometry->ComputeInvalidationRegion()));
+#ifdef MOZ_DUMP_PAINTING
+    if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+      printf_stderr("Display item type %s(%p) (in layer %p) belongs to an invalidated frame!\n", item->Name(), item->Frame(), aData->mLayer.get());
+    }
+#endif
+  } else {
+    // Let the display item check for geometry changes and decide what needs to be
+    // repainted.
+
+    const nsTArray<nsIFrame*>& changedFrames = aData->GetFrameListChanges();
+    aData->mGeometry->MoveBy(shift);
+    item->ComputeInvalidationRegion(mDisplayListBuilder, aData->mGeometry, &combined);
+
+    // We have an optimization to cache the drawing of background-attachment: fixed canvas
+    // background images so we can scroll and just blit them when they are flattened into
+    // the same layer as scrolling content. NotifyRenderingChanged is only used to tell
+    // the canvas bg image item to purge this cache. We want to be careful not to accidentally
+    // purge the cache if we are just invalidating due to scrolling (ie the background image
+    // moves on the scrolling layer but it's rendering stays the same) so if
+    // AddOffsetAndComputeDifference is the only thing that will invalidate we skip the
+    // NotifyRenderingChanged call (ComputeInvalidationRegion for background images also calls
+    // NotifyRenderingChanged if anything changes).
+    // Only allocate a new geometry object if something actually changed, otherwise the existing
+    // one should be fine. We always reallocate for inactive layers, since these types don't
+    // implement ComputeInvalidateRegion (and rely on the ComputeDifferences call in
+    // AddPaintedDisplayItem instead).
+    if (!combined.IsEmpty() || aData->mLayerState == LAYER_INACTIVE) {
+      geometry = item->AllocateGeometry(mDisplayListBuilder);
+    } else if (aData->mClip == clip && invalid.IsEmpty() && changedFrames.Length() == 0) {
+      notifyRenderingChanged = false;
+    }
+    aData->mClip.AddOffsetAndComputeDifference(entry->mCommonClipCount,
+                                               shift, aData->mGeometry->ComputeInvalidationRegion(),
+                                               clip, entry->mLastCommonClipCount,
+                                               geometry ? geometry->ComputeInvalidationRegion() :
+                                                          aData->mGeometry->ComputeInvalidationRegion(),
+                                               &combined);
+
+    // Add in any rect that the frame specified
+    combined.Or(combined, invalid);
+
+    for (uint32_t i = 0; i < changedFrames.Length(); i++) {
+      combined.Or(combined, changedFrames[i]->GetVisualOverflowRect());
+    }
+
+    // Restrict invalidation to the clipped region
+    nsRegion clipRegion;
+    if (clip.ComputeRegionInClips(&aData->mClip, shift, &clipRegion)) {
+      combined.And(combined, clipRegion);
+    }
+#ifdef MOZ_DUMP_PAINTING
+    if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+      if (!combined.IsEmpty()) {
+        printf_stderr("Display item type %s(%p) (in layer %p) changed geometry!\n", item->Name(), item->Frame(), aData->mLayer.get());
+      }
+    }
+#endif
+  }
+  if (!combined.IsEmpty()) {
+    if (notifyRenderingChanged) {
+      item->NotifyRenderingChanged();
+    }
+    InvalidatePostTransformRegion(paintedLayer,
+        combined.ScaleToOutsidePixels(layerData->mXScale, layerData->mYScale, layerData->mAppUnitsPerDevPixel),
+        layerData->mTranslation);
+  }
+
+  aData->EndUpdate(geometry);
+}
+
+void
+FrameLayerBuilder::AddPaintedDisplayItem(PaintedLayerData* aLayerData,
+                                        nsDisplayItem* aItem,
+                                        const DisplayItemClip& aClip,
+                                        ContainerState& aContainerState,
+                                        LayerState aLayerState,
+                                        const nsPoint& aTopLeft)
+{
+  PaintedLayer* layer = aLayerData->mLayer;
+  PaintedDisplayItemLayerUserData* paintedData =
+    static_cast<PaintedDisplayItemLayerUserData*>
+      (layer->GetUserData(&gPaintedDisplayItemLayerUserData));
+  RefPtr<BasicLayerManager> tempManager;
+  nsIntRect intClip;
+  bool hasClip = false;
+  if (aLayerState != LAYER_NONE) {
+    DisplayItemData *data = GetDisplayItemDataForManager(aItem, layer->Manager());
+    if (data) {
+      tempManager = data->mInactiveManager;
+    }
+    if (!tempManager) {
+      tempManager = new BasicLayerManager(BasicLayerManager::BLM_INACTIVE);
+    }
+
+    // We need to grab these before calling AddLayerDisplayItem because it will overwrite them.
+    nsRegion clip;
+    DisplayItemClip* oldClip = nullptr;
+    GetOldLayerFor(aItem, nullptr, &oldClip);
+    hasClip = aClip.ComputeRegionInClips(oldClip,
+                                         aTopLeft - paintedData->mLastAnimatedGeometryRootOrigin,
+                                         &clip);
+
+    if (hasClip) {
+      intClip = clip.GetBounds().ScaleToOutsidePixels(paintedData->mXScale,
+                                                      paintedData->mYScale,
+                                                      paintedData->mAppUnitsPerDevPixel);
+    }
+  }
+
+  AddLayerDisplayItem(layer, aItem, aLayerState, tempManager);
+
+  PaintedLayerItemsEntry* entry = mPaintedLayerItems.PutEntry(layer);
+  if (entry) {
+    entry->mContainerLayerFrame = aContainerState.GetContainerFrame();
+    if (entry->mContainerLayerGeneration == 0) {
+      entry->mContainerLayerGeneration = mContainerLayerGeneration;
+    }
+    if (tempManager) {
+      FLB_LOG_PAINTED_LAYER_DECISION(aLayerData, "Creating nested FLB for item %p\n", aItem);
+      FrameLayerBuilder* layerBuilder = new FrameLayerBuilder();
+      layerBuilder->Init(mDisplayListBuilder, tempManager, aLayerData);
+
+      tempManager->BeginTransaction();
+      if (mRetainingManager) {
+        layerBuilder->DidBeginRetainedLayerTransaction(tempManager);
+      }
+
+      UniquePtr<LayerProperties> props(LayerProperties::CloneFrom(tempManager->GetRoot()));
+      RefPtr<Layer> tmpLayer =
+        aItem->BuildLayer(mDisplayListBuilder, tempManager, ContainerLayerParameters());
+      // We have no easy way of detecting if this transaction will ever actually get finished.
+      // For now, I've just silenced the warning with nested transactions in BasicLayers.cpp
+      if (!tmpLayer) {
+        tempManager->EndTransaction(nullptr, nullptr);
+        tempManager->SetUserData(&gLayerManagerLayerBuilder, nullptr);
+        return;
+      }
+
+      bool snap;
+      nsRect visibleRect =
+        aItem->GetVisibleRect().Intersect(aItem->GetBounds(mDisplayListBuilder, &snap));
+      nsIntRegion rgn = visibleRect.ToOutsidePixels(paintedData->mAppUnitsPerDevPixel);
+      SetOuterVisibleRegion(tmpLayer, &rgn);
+
+      // If BuildLayer didn't call BuildContainerLayerFor, then our new layer won't have been
+      // stored in layerBuilder. Manually add it now.
+      if (mRetainingManager) {
+#ifdef DEBUG_DISPLAY_ITEM_DATA
+        LayerManagerData* parentLmd = static_cast<LayerManagerData*>
+          (layer->Manager()->GetUserData(&gLayerManagerUserData));
+        LayerManagerData* lmd = static_cast<LayerManagerData*>
+          (tempManager->GetUserData(&gLayerManagerUserData));
+        lmd->mParent = parentLmd;
+#endif
+        layerBuilder->StoreDataForFrame(aItem, tmpLayer, LAYER_ACTIVE);
+      }
+
+      tempManager->SetRoot(tmpLayer);
+      layerBuilder->WillEndTransaction();
+      tempManager->AbortTransaction();
+
+#ifdef MOZ_DUMP_PAINTING
+      if (gfxUtils::DumpDisplayList() || gfxEnv::DumpPaint()) {
+        fprintf_stderr(gfxUtils::sDumpPaintFile, "Basic layer tree for painting contents of display item %s(%p):\n", aItem->Name(), aItem->Frame());
+        std::stringstream stream;
+        tempManager->Dump(stream, "", gfxEnv::DumpPaintToFile());
+        fprint_stderr(gfxUtils::sDumpPaintFile, stream);  // not a typo, fprint_stderr declared in LayersLogging.h
+      }
+#endif
+
+      nsIntPoint offset = GetLastPaintOffset(layer) - GetTranslationForPaintedLayer(layer);
+      props->MoveBy(-offset);
+      // Effective transforms are needed by ComputeDifferences().
+      tmpLayer->ComputeEffectiveTransforms(Matrix4x4());
+      nsIntRegion invalid = props->ComputeDifferences(tmpLayer, nullptr);
+      if (aLayerState == LAYER_SVG_EFFECTS) {
+        invalid = nsSVGIntegrationUtils::AdjustInvalidAreaForSVGEffects(aItem->Frame(),
+                                                                        aItem->ToReferenceFrame(),
+                                                                        invalid);
+      }
+      if (!invalid.IsEmpty()) {
+#ifdef MOZ_DUMP_PAINTING
+        if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+          printf_stderr("Inactive LayerManager(%p) for display item %s(%p) has an invalid region - invalidating layer %p\n", tempManager.get(), aItem->Name(), aItem->Frame(), layer);
+        }
+#endif
+        invalid.ScaleRoundOut(paintedData->mXScale, paintedData->mYScale);
+
+        if (hasClip) {
+          invalid.And(invalid, intClip);
+        }
+
+        InvalidatePostTransformRegion(layer, invalid,
+                                      GetTranslationForPaintedLayer(layer));
+      }
+    }
+    ClippedDisplayItem* cdi =
+      entry->mItems.AppendElement(ClippedDisplayItem(aItem,
+                                                     mContainerLayerGeneration));
+    cdi->mInactiveLayerManager = tempManager;
+  }
+}
+
+FrameLayerBuilder::DisplayItemData*
+FrameLayerBuilder::StoreDataForFrame(nsDisplayItem* aItem, Layer* aLayer, LayerState aState)
+{
+  DisplayItemData* oldData = GetDisplayItemDataForManager(aItem, mRetainingManager);
+  if (oldData) {
+    if (!oldData->mUsed) {
+      oldData->BeginUpdate(aLayer, aState, mContainerLayerGeneration, aItem);
+    }
+    return oldData;
+  }
+
+  LayerManagerData* lmd = static_cast<LayerManagerData*>
+    (mRetainingManager->GetUserData(&gLayerManagerUserData));
+
+  RefPtr<DisplayItemData> data =
+    new DisplayItemData(lmd, aItem->GetPerFrameKey(), aLayer);
+
+  data->BeginUpdate(aLayer, aState, mContainerLayerGeneration, aItem);
+
+  lmd->mDisplayItems.PutEntry(data);
+  return data;
+}
+
+void
+FrameLayerBuilder::StoreDataForFrame(nsIFrame* aFrame,
+                                     uint32_t aDisplayItemKey,
+                                     Layer* aLayer,
+                                     LayerState aState)
+{
+  DisplayItemData* oldData = GetDisplayItemData(aFrame, aDisplayItemKey);
+  if (oldData && oldData->mFrameList.Length() == 1) {
+    oldData->BeginUpdate(aLayer, aState, mContainerLayerGeneration);
+    return;
+  }
+
+  LayerManagerData* lmd = static_cast<LayerManagerData*>
+    (mRetainingManager->GetUserData(&gLayerManagerUserData));
+
+  RefPtr<DisplayItemData> data =
+    new DisplayItemData(lmd, aDisplayItemKey, aLayer, aFrame);
+
+  data->BeginUpdate(aLayer, aState, mContainerLayerGeneration);
+
+  lmd->mDisplayItems.PutEntry(data);
+}
+
+FrameLayerBuilder::ClippedDisplayItem::ClippedDisplayItem(nsDisplayItem* aItem,
+                                                          uint32_t aGeneration)
+  : mItem(aItem)
+  , mContainerLayerGeneration(aGeneration)
+{
+}
+
+FrameLayerBuilder::ClippedDisplayItem::~ClippedDisplayItem()
+{
+  if (mInactiveLayerManager) {
+    mInactiveLayerManager->SetUserData(&gLayerManagerLayerBuilder, nullptr);
+  }
+}
+
+FrameLayerBuilder::PaintedLayerItemsEntry::PaintedLayerItemsEntry(const PaintedLayer *aKey)
+  : nsPtrHashKey<PaintedLayer>(aKey)
+  , mContainerLayerFrame(nullptr)
+  , mLastCommonClipCount(0)
+  , mContainerLayerGeneration(0)
+  , mHasExplicitLastPaintOffset(false)
+  , mCommonClipCount(0)
+{
+}
+
+FrameLayerBuilder::PaintedLayerItemsEntry::PaintedLayerItemsEntry(const PaintedLayerItemsEntry& aOther)
+  : nsPtrHashKey<PaintedLayer>(aOther.mKey)
+  , mItems(aOther.mItems)
+{
+  NS_ERROR("Should never be called, since we ALLOW_MEMMOVE");
+}
+
+FrameLayerBuilder::PaintedLayerItemsEntry::~PaintedLayerItemsEntry()
+{
+}
+
+void
+FrameLayerBuilder::AddLayerDisplayItem(Layer* aLayer,
+                                       nsDisplayItem* aItem,
+                                       LayerState aLayerState,
+                                       BasicLayerManager* aManager)
+{
+  if (aLayer->Manager() != mRetainingManager)
+    return;
+
+  DisplayItemData *data = StoreDataForFrame(aItem, aLayer, aLayerState);
+  data->mInactiveManager = aManager;
+}
+
+nsIntPoint
+FrameLayerBuilder::GetLastPaintOffset(PaintedLayer* aLayer)
+{
+  PaintedLayerItemsEntry* entry = mPaintedLayerItems.PutEntry(aLayer);
+  if (entry) {
+    if (entry->mContainerLayerGeneration == 0) {
+      entry->mContainerLayerGeneration = mContainerLayerGeneration;
+    }
+    if (entry->mHasExplicitLastPaintOffset)
+      return entry->mLastPaintOffset;
+  }
+  return GetTranslationForPaintedLayer(aLayer);
+}
+
+void
+FrameLayerBuilder::SavePreviousDataForLayer(PaintedLayer* aLayer, uint32_t aClipCount)
+{
+  PaintedLayerItemsEntry* entry = mPaintedLayerItems.PutEntry(aLayer);
+  if (entry) {
+    if (entry->mContainerLayerGeneration == 0) {
+      entry->mContainerLayerGeneration = mContainerLayerGeneration;
+    }
+    entry->mLastPaintOffset = GetTranslationForPaintedLayer(aLayer);
+    entry->mHasExplicitLastPaintOffset = true;
+    entry->mLastCommonClipCount = aClipCount;
+  }
+}
+
+bool
+FrameLayerBuilder::CheckInLayerTreeCompressionMode()
+{
+  if (mInLayerTreeCompressionMode) {
+    return true;
+  }
+
+  // If we wanted to be in layer tree compression mode, but weren't, then scheduled
+  // a delayed repaint where we will be.
+  mRootPresContext->PresShell()->GetRootFrame()->SchedulePaint(nsIFrame::PAINT_DELAYED_COMPRESS);
+
+  return false;
+}
+
+void
+ContainerState::CollectOldLayers()
+{
+  for (Layer* layer = mContainerLayer->GetFirstChild(); layer;
+       layer = layer->GetNextSibling()) {
+    NS_ASSERTION(!layer->HasUserData(&gMaskLayerUserData),
+                 "Mask layers should not be part of the layer tree.");
+    if (layer->HasUserData(&gPaintedDisplayItemLayerUserData)) {
+      NS_ASSERTION(layer->AsPaintedLayer(), "Wrong layer type");
+      mPaintedLayersAvailableForRecycling.PutEntry(static_cast<PaintedLayer*>(layer));
+    }
+
+    if (Layer* maskLayer = layer->GetMaskLayer()) {
+      NS_ASSERTION(maskLayer->GetType() == Layer::TYPE_IMAGE,
+                   "Could not recycle mask layer, unsupported layer type.");
+      mRecycledMaskImageLayers.Put(MaskLayerKey(layer, Nothing()), static_cast<ImageLayer*>(maskLayer));
+    }
+    for (size_t i = 0; i < layer->GetAncestorMaskLayerCount(); i++) {
+      Layer* maskLayer = layer->GetAncestorMaskLayerAt(i);
+
+      NS_ASSERTION(maskLayer->GetType() == Layer::TYPE_IMAGE,
+                   "Could not recycle mask layer, unsupported layer type.");
+      mRecycledMaskImageLayers.Put(MaskLayerKey(layer, Some(i)), static_cast<ImageLayer*>(maskLayer));
+    }
+  }
+}
+
+struct OpaqueRegionEntry {
+  AnimatedGeometryRoot* mAnimatedGeometryRoot;
+  nsIntRegion mOpaqueRegion;
+};
+
+static OpaqueRegionEntry*
+FindOpaqueRegionEntry(nsTArray<OpaqueRegionEntry>& aEntries,
+                      AnimatedGeometryRoot* aAnimatedGeometryRoot)
+{
+  for (uint32_t i = 0; i < aEntries.Length(); ++i) {
+    OpaqueRegionEntry* d = &aEntries[i];
+    if (d->mAnimatedGeometryRoot == aAnimatedGeometryRoot) {
+      return d;
+    }
+  }
+  return nullptr;
+}
+
+void
+ContainerState::SetupScrollingMetadata(NewLayerEntry* aEntry)
+{
+  if (mFlattenToSingleLayer) {
+    // animated geometry roots are forced to all match, so we can't
+    // use them and we don't get async scrolling.
+    return;
+  }
+
+  if (!mBuilder->IsPaintingToWindow()) {
+    // async scrolling not possible, and async scrolling info not computed
+    // for this paint.
+    return;
+  }
+
+  AutoTArray<ScrollMetadata,2> metricsArray;
+  if (aEntry->mBaseScrollMetadata) {
+    metricsArray.AppendElement(*aEntry->mBaseScrollMetadata);
+
+    // The base FrameMetrics was not computed by the nsIScrollableframe, so it
+    // should not have a mask layer.
+    MOZ_ASSERT(!aEntry->mBaseScrollMetadata->HasMaskLayer());
+  }
+
+  // Any extra mask layers we need to attach to ScrollMetadatas.
+  // The list may already contain an entry added for the layer's scrolled clip
+  // so add to it rather than overwriting it (we clear the list when recycling
+  // a layer).
+  nsTArray<RefPtr<Layer>> maskLayers(aEntry->mLayer->GetAllAncestorMaskLayers());
+
+  for (const DisplayItemScrollClip* scrollClip = aEntry->mScrollClip;
+       scrollClip && scrollClip != mContainerScrollClip;
+       scrollClip = scrollClip->mParent) {
+    if (!scrollClip->mIsAsyncScrollable) {
+      // This scroll clip was created for a scroll frame that didn't know
+      // whether it needs to be async scrollable for scroll handoff. It was
+      // not activated, so we don't need to create a frame metrics for it.
+      continue;
+    }
+
+    nsIScrollableFrame* scrollFrame = scrollClip->mScrollableFrame;
+    const DisplayItemClip* clip = scrollClip->mClip;
+
+    Maybe<ScrollMetadata> metadata =
+      scrollFrame->ComputeScrollMetadata(aEntry->mLayer, mContainerReferenceFrame, mParameters, clip);
+    if (!metadata) {
+      continue;
+    }
+
+    if (clip &&
+        clip->HasClip() &&
+        clip->GetRoundedRectCount() > 0)
+    {
+      // The clip in between this scrollframe and its ancestor scrollframe
+      // requires a mask layer. Since this mask layer should not move with
+      // the APZC associated with this FrameMetrics, we attach the mask
+      // layer as an additional, separate clip.
+      Maybe<size_t> nextIndex = Some(maskLayers.Length());
+      RefPtr<Layer> maskLayer =
+        CreateMaskLayer(aEntry->mLayer, *clip, nextIndex, clip->GetRoundedRectCount());
+      if (maskLayer) {
+        MOZ_ASSERT(metadata->HasScrollClip());
+        metadata->ScrollClip().SetMaskLayerIndex(nextIndex);
+        maskLayers.AppendElement(maskLayer);
+      }
+    }
+
+    metricsArray.AppendElement(*metadata);
+  }
+
+  // Watch out for FrameMetrics copies in profiles
+  aEntry->mLayer->SetScrollMetadata(metricsArray);
+  aEntry->mLayer->SetAncestorMaskLayers(maskLayers);
+}
+
+static inline Maybe<ParentLayerIntRect>
+GetStationaryClipInContainer(Layer* aLayer)
+{
+  if (size_t metricsCount = aLayer->GetScrollMetadataCount()) {
+    return aLayer->GetScrollMetadata(metricsCount - 1).GetClipRect();
+  }
+  return aLayer->GetClipRect();
+}
+
+void
+ContainerState::PostprocessRetainedLayers(nsIntRegion* aOpaqueRegionForContainer)
+{
+  AutoTArray<OpaqueRegionEntry,4> opaqueRegions;
+  bool hideAll = false;
+  int32_t opaqueRegionForContainer = -1;
+
+  for (int32_t i = mNewChildLayers.Length() - 1; i >= 0; --i) {
+    NewLayerEntry* e = &mNewChildLayers.ElementAt(i);
+    if (!e->mLayer) {
+      continue;
+    }
+
+    OpaqueRegionEntry* data = FindOpaqueRegionEntry(opaqueRegions, e->mAnimatedGeometryRoot);
+
+    SetupScrollingMetadata(e);
+
+    if (hideAll) {
+      e->mVisibleRegion.SetEmpty();
+    } else if (!e->mLayer->IsScrollbarContainer()) {
+      Maybe<ParentLayerIntRect> clipRect = GetStationaryClipInContainer(e->mLayer);
+      if (clipRect && opaqueRegionForContainer >= 0 &&
+          opaqueRegions[opaqueRegionForContainer].mOpaqueRegion.Contains(clipRect->ToUnknownRect())) {
+        e->mVisibleRegion.SetEmpty();
+      } else if (data) {
+        e->mVisibleRegion.Sub(e->mVisibleRegion, data->mOpaqueRegion);
+      }
+    }
+
+    SetOuterVisibleRegionForLayer(e->mLayer,
+                                  e->mVisibleRegion,
+                                  e->mLayerContentsVisibleRect.width >= 0 ? &e->mLayerContentsVisibleRect : nullptr,
+                                  e->mUntransformedVisibleRegion);
+
+    if (!e->mOpaqueRegion.IsEmpty()) {
+      AnimatedGeometryRoot* animatedGeometryRootToCover = e->mAnimatedGeometryRoot;
+      if (e->mOpaqueForAnimatedGeometryRootParent &&
+          e->mAnimatedGeometryRoot->mParentAGR == mContainerAnimatedGeometryRoot) {
+        animatedGeometryRootToCover = mContainerAnimatedGeometryRoot;
+        data = FindOpaqueRegionEntry(opaqueRegions, animatedGeometryRootToCover);
+      }
+
+      if (!data) {
+        if (animatedGeometryRootToCover == mContainerAnimatedGeometryRoot) {
+          NS_ASSERTION(opaqueRegionForContainer == -1, "Already found it?");
+          opaqueRegionForContainer = opaqueRegions.Length();
+        }
+        data = opaqueRegions.AppendElement();
+        data->mAnimatedGeometryRoot = animatedGeometryRootToCover;
+      }
+
+      nsIntRegion clippedOpaque = e->mOpaqueRegion;
+      Maybe<ParentLayerIntRect> clipRect = e->mLayer->GetCombinedClipRect();
+      if (clipRect) {
+        clippedOpaque.AndWith(clipRect->ToUnknownRect());
+      }
+      if (e->mLayer->GetIsFixedPosition() && e->mLayer->GetScrolledClip()) {
+        // The clip can move asynchronously, so we can't rely on opaque parts
+        // staying in the same place.
+        clippedOpaque.SetEmpty();
+      } else if (e->mHideAllLayersBelow) {
+        hideAll = true;
+      }
+      data->mOpaqueRegion.Or(data->mOpaqueRegion, clippedOpaque);
+    }
+
+    if (e->mLayer->GetType() == Layer::TYPE_READBACK) {
+      // ReadbackLayers need to accurately read what's behind them. So,
+      // we don't want to do any occlusion culling of layers behind them.
+      // Theoretically we could just punch out the ReadbackLayer's rectangle
+      // from all mOpaqueRegions, but that's probably not worth doing.
+      opaqueRegions.Clear();
+      opaqueRegionForContainer = -1;
+    }
+  }
+
+  if (opaqueRegionForContainer >= 0) {
+    aOpaqueRegionForContainer->Or(*aOpaqueRegionForContainer,
+        opaqueRegions[opaqueRegionForContainer].mOpaqueRegion);
+  }
+}
+
+void
+ContainerState::Finish(uint32_t* aTextContentFlags,
+                       const nsIntRect& aContainerPixelBounds,
+                       nsDisplayList* aChildItems, bool* aHasComponentAlphaChildren)
+{
+  mPaintedLayerDataTree.Finish();
+
+  if (!mParameters.mForEventsAndPluginsOnly) {
+    NS_ASSERTION(mContainerBounds.IsEqualInterior(mAccumulatedChildBounds),
+                 "Bounds computation mismatch");
+  }
+
+  if (mLayerBuilder->IsBuildingRetainedLayers()) {
+    nsIntRegion containerOpaqueRegion;
+    PostprocessRetainedLayers(&containerOpaqueRegion);
+    if (containerOpaqueRegion.Contains(aContainerPixelBounds)) {
+      aChildItems->SetIsOpaque();
+    }
+  }
+
+  uint32_t textContentFlags = 0;
+
+  // Make sure that current/existing layers are added to the parent and are
+  // in the correct order.
+  Layer* layer = nullptr;
+  Layer* prevChild = nullptr;
+  for (uint32_t i = 0; i < mNewChildLayers.Length(); ++i, prevChild = layer) {
+    if (!mNewChildLayers[i].mLayer) {
+      continue;
+    }
+
+    layer = mNewChildLayers[i].mLayer;
+
+    if (!layer->GetVisibleRegion().IsEmpty()) {
+      textContentFlags |=
+        layer->GetContentFlags() & (Layer::CONTENT_COMPONENT_ALPHA |
+                                    Layer::CONTENT_COMPONENT_ALPHA_DESCENDANT |
+                                    Layer::CONTENT_DISABLE_FLATTENING);
+
+      // Notify the parent of component alpha children unless it's coming from
+      // within a child that has asked not to contribute to layer flattening.
+      if (aHasComponentAlphaChildren &&
+          mNewChildLayers[i].mPropagateComponentAlphaFlattening &&
+          (layer->GetContentFlags() & Layer::CONTENT_COMPONENT_ALPHA)) {
+
+        for (int32_t j = i - 1; j >= 0; j--) {
+          if (mNewChildLayers[j].mVisibleRegion.Intersects(mNewChildLayers[i].mVisibleRegion.GetBounds())) {
+            if (mNewChildLayers[j].mLayerState != LAYER_ACTIVE_FORCE) {
+              *aHasComponentAlphaChildren = true;
+            }
+            break;
+
+          }
+
+        }
+      }
+    }
+
+    if (!layer->GetParent()) {
+      // This is not currently a child of the container, so just add it
+      // now.
+      mContainerLayer->InsertAfter(layer, prevChild);
+    } else {
+      NS_ASSERTION(layer->GetParent() == mContainerLayer,
+                   "Layer shouldn't be the child of some other container");
+      if (layer->GetPrevSibling() != prevChild) {
+        mContainerLayer->RepositionChild(layer, prevChild);
+      }
+    }
+  }
+
+  // Remove old layers that have become unused.
+  if (!layer) {
+    layer = mContainerLayer->GetFirstChild();
+  } else {
+    layer = layer->GetNextSibling();
+  }
+  while (layer) {
+    Layer *layerToRemove = layer;
+    layer = layer->GetNextSibling();
+    mContainerLayer->RemoveChild(layerToRemove);
+  }
+
+  *aTextContentFlags = textContentFlags;
+}
+
+static inline gfxSize RoundToFloatPrecision(const gfxSize& aSize)
+{
+  return gfxSize(float(aSize.width), float(aSize.height));
+}
+
+static void RestrictScaleToMaxLayerSize(gfxSize& aScale,
+                                        const nsRect& aVisibleRect,
+                                        nsIFrame* aContainerFrame,
+                                        Layer* aContainerLayer)
+{
+  if (!aContainerLayer->Manager()->IsWidgetLayerManager()) {
+    return;
+  }
+
+  nsIntRect pixelSize =
+    aVisibleRect.ScaleToOutsidePixels(aScale.width, aScale.height,
+                                      aContainerFrame->PresContext()->AppUnitsPerDevPixel());
+
+  int32_t maxLayerSize = aContainerLayer->GetMaxLayerSize();
+
+  if (pixelSize.width > maxLayerSize) {
+    float scale = (float)pixelSize.width / maxLayerSize;
+    scale = gfxUtils::ClampToScaleFactor(scale);
+    aScale.width /= scale;
+  }
+  if (pixelSize.height > maxLayerSize) {
+    float scale = (float)pixelSize.height / maxLayerSize;
+    scale = gfxUtils::ClampToScaleFactor(scale);
+    aScale.height /= scale;
+  }
+}
+static bool
+ChooseScaleAndSetTransform(FrameLayerBuilder* aLayerBuilder,
+                           nsDisplayListBuilder* aDisplayListBuilder,
+                           nsIFrame* aContainerFrame,
+                           nsDisplayItem* aContainerItem,
+                           const nsRect& aVisibleRect,
+                           const Matrix4x4* aTransform,
+                           const ContainerLayerParameters& aIncomingScale,
+                           ContainerLayer* aLayer,
+                           LayerState aState,
+                           ContainerLayerParameters& aOutgoingScale)
+{
+  nsIntPoint offset;
+
+  Matrix4x4 transform =
+    Matrix4x4::Scaling(aIncomingScale.mXScale, aIncomingScale.mYScale, 1.0);
+  if (aTransform) {
+    // aTransform is applied first, then the scale is applied to the result
+    transform = (*aTransform)*transform;
+    // Set any matrix entries close to integers to be those exact integers.
+    // This protects against floating-point inaccuracies causing problems
+    // in the checks below.
+    // We use the fixed epsilon version here because we don't want the nudging
+    // to depend on the scroll position.
+    transform.NudgeToIntegersFixedEpsilon();
+  }
+  Matrix transform2d;
+  if (aContainerFrame &&
+      (aState == LAYER_INACTIVE || aState == LAYER_SVG_EFFECTS) &&
+      (!aTransform || (aTransform->Is2D(&transform2d) &&
+                       !transform2d.HasNonTranslation()))) {
+    // When we have an inactive ContainerLayer, translate the container by the offset to the
+    // reference frame (and offset all child layers by the reverse) so that the coordinate
+    // space of the child layers isn't affected by scrolling.
+    // This gets confusing for complicated transform (since we'd have to compute the scale
+    // factors for the matrix), so we don't bother. Any frames that are building an nsDisplayTransform
+    // for a css transform would have 0,0 as their offset to the reference frame, so this doesn't
+    // matter.
+    nsPoint appUnitOffset = aDisplayListBuilder->ToReferenceFrame(aContainerFrame);
+    nscoord appUnitsPerDevPixel = aContainerFrame->PresContext()->AppUnitsPerDevPixel();
+    offset = nsIntPoint(
+        NS_lround(NSAppUnitsToDoublePixels(appUnitOffset.x, appUnitsPerDevPixel)*aIncomingScale.mXScale),
+        NS_lround(NSAppUnitsToDoublePixels(appUnitOffset.y, appUnitsPerDevPixel)*aIncomingScale.mYScale));
+  }
+  transform.PostTranslate(offset.x + aIncomingScale.mOffset.x,
+                          offset.y + aIncomingScale.mOffset.y,
+                          0);
+
+  if (transform.IsSingular()) {
+    return false;
+  }
+
+  bool canDraw2D = transform.CanDraw2D(&transform2d);
+  gfxSize scale;
+  // XXX Should we do something for 3D transforms?
+  if (canDraw2D &&
+      !aContainerFrame->Combines3DTransformWithAncestors() &&
+      !aContainerFrame->HasPerspective()) {
+    // If the container's transform is animated off main thread, fix a suitable scale size
+    // for animation
+    if (aContainerItem &&
+        aContainerItem->GetType() == nsDisplayItem::TYPE_TRANSFORM &&
+        EffectCompositor::HasAnimationsForCompositor(
+          aContainerFrame, eCSSProperty_transform)) {
+      // Use the size of the nearest widget as the maximum size.  This
+      // is important since it might be a popup that is bigger than the
+      // pres context's size.
+      nsPresContext* presContext = aContainerFrame->PresContext();
+      nsIWidget* widget = aContainerFrame->GetNearestWidget();
+      nsSize displaySize;
+      if (widget) {
+        LayoutDeviceIntSize widgetSize = widget->GetClientSize();
+        int32_t p2a = presContext->AppUnitsPerDevPixel();
+        displaySize.width = NSIntPixelsToAppUnits(widgetSize.width, p2a);
+        displaySize.height = NSIntPixelsToAppUnits(widgetSize.height, p2a);
+      } else {
+        displaySize = presContext->GetVisibleArea().Size();
+      }
+      // compute scale using the animation on the container (ignoring
+      // its ancestors)
+      scale = nsLayoutUtils::ComputeSuitableScaleForAnimation(
+                aContainerFrame, aVisibleRect.Size(),
+                displaySize);
+      // multiply by the scale inherited from ancestors--we use a uniform
+      // scale factor to prevent blurring when the layer is rotated.
+      float incomingScale = std::max(aIncomingScale.mXScale, aIncomingScale.mYScale);
+      scale.width *= incomingScale;
+      scale.height *= incomingScale;
+    } else {
+      // Scale factors are normalized to a power of 2 to reduce the number of resolution changes
+      scale = RoundToFloatPrecision(ThebesMatrix(transform2d).ScaleFactors(true));
+      // For frames with a changing transform that's not just a translation,
+      // round scale factors up to nearest power-of-2 boundary so that we don't
+      // keep having to redraw the content as it scales up and down. Rounding up to nearest
+      // power-of-2 boundary ensures we never scale up, only down --- avoiding
+      // jaggies. It also ensures we never scale down by more than a factor of 2,
+      // avoiding bad downscaling quality.
+      Matrix frameTransform;
+      if (ActiveLayerTracker::IsStyleAnimated(aDisplayListBuilder, aContainerFrame, eCSSProperty_transform) &&
+          aTransform &&
+          (!aTransform->Is2D(&frameTransform) || frameTransform.HasNonTranslationOrFlip())) {
+        // Don't clamp the scale factor when the new desired scale factor matches the old one
+        // or it was previously unscaled.
+        bool clamp = true;
+        Matrix oldFrameTransform2d;
+        if (aLayer->GetBaseTransform().Is2D(&oldFrameTransform2d)) {
+          gfxSize oldScale = RoundToFloatPrecision(ThebesMatrix(oldFrameTransform2d).ScaleFactors(true));
+          if (oldScale == scale || oldScale == gfxSize(1.0, 1.0)) {
+            clamp = false;
+          }
+        }
+        if (clamp) {
+          scale.width = gfxUtils::ClampToScaleFactor(scale.width);
+          scale.height = gfxUtils::ClampToScaleFactor(scale.height);
+        }
+      } else {
+        // XXX Do we need to move nearly-integer values to integers here?
+      }
+    }
+    // If the scale factors are too small, just use 1.0. The content is being
+    // scaled out of sight anyway.
+    if (fabs(scale.width) < 1e-8 || fabs(scale.height) < 1e-8) {
+      scale = gfxSize(1.0, 1.0);
+    }
+    // If this is a transform container layer, then pre-rendering might
+    // mean we try render a layer bigger than the max texture size. If we have
+    // tiling, that's not a problem, since we'll automatically choose a tiled
+    // layer for layers of that size. If not, we need to apply clamping to
+    // prevent this.
+    if (aTransform && !gfxPrefs::LayersTilesEnabled()) {
+      RestrictScaleToMaxLayerSize(scale, aVisibleRect, aContainerFrame, aLayer);
+    }
+  } else {
+    scale = gfxSize(1.0, 1.0);
+  }
+
+  // Store the inverse of our resolution-scale on the layer
+  aLayer->SetBaseTransform(transform);
+  aLayer->SetPreScale(1.0f/float(scale.width),
+                      1.0f/float(scale.height));
+  aLayer->SetInheritedScale(aIncomingScale.mXScale,
+                            aIncomingScale.mYScale);
+
+  aOutgoingScale =
+    ContainerLayerParameters(scale.width, scale.height, -offset, aIncomingScale);
+  if (aTransform) {
+    aOutgoingScale.mInTransformedSubtree = true;
+    if (ActiveLayerTracker::IsStyleAnimated(aDisplayListBuilder, aContainerFrame,
+                                            eCSSProperty_transform)) {
+      aOutgoingScale.mInActiveTransformedSubtree = true;
+    }
+  }
+  if ((aLayerBuilder->IsBuildingRetainedLayers() &&
+       (!canDraw2D || transform2d.HasNonIntegerTranslation())) ||
+      aContainerFrame->Extend3DContext() ||
+      aContainerFrame->Combines3DTransformWithAncestors()) {
+    aOutgoingScale.mDisableSubpixelAntialiasingInDescendants = true;
+  }
+  return true;
+}
+
+already_AddRefed<ContainerLayer>
+FrameLayerBuilder::BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
+                                          LayerManager* aManager,
+                                          nsIFrame* aContainerFrame,
+                                          nsDisplayItem* aContainerItem,
+                                          nsDisplayList* aChildren,
+                                          const ContainerLayerParameters& aParameters,
+                                          const Matrix4x4* aTransform,
+                                          uint32_t aFlags)
+{
+  uint32_t containerDisplayItemKey =
+    aContainerItem ? aContainerItem->GetPerFrameKey() : nsDisplayItem::TYPE_ZERO;
+  NS_ASSERTION(aContainerFrame, "Container display items here should have a frame");
+  NS_ASSERTION(!aContainerItem ||
+               aContainerItem->Frame() == aContainerFrame,
+               "Container display item must match given frame");
+
+  if (!aParameters.mXScale || !aParameters.mYScale) {
+    return nullptr;
+  }
+
+  RefPtr<ContainerLayer> containerLayer;
+  if (aManager == mRetainingManager) {
+    // Using GetOldLayerFor will search merged frames, as well as the underlying
+    // frame. The underlying frame can change when a page scrolls, so this
+    // avoids layer recreation in the situation that a new underlying frame is
+    // picked for a layer.
+    Layer* oldLayer = nullptr;
+    if (aContainerItem) {
+      oldLayer = GetOldLayerFor(aContainerItem);
+    } else {
+      DisplayItemData *data = GetOldLayerForFrame(aContainerFrame, containerDisplayItemKey);
+      if (data) {
+        oldLayer = data->mLayer;
+      }
+    }
+
+    if (oldLayer) {
+      NS_ASSERTION(oldLayer->Manager() == aManager, "Wrong manager");
+      if (oldLayer->HasUserData(&gPaintedDisplayItemLayerUserData)) {
+        // The old layer for this item is actually our PaintedLayer
+        // because we rendered its layer into that PaintedLayer. So we
+        // don't actually have a retained container layer.
+      } else {
+        NS_ASSERTION(oldLayer->GetType() == Layer::TYPE_CONTAINER,
+                     "Wrong layer type");
+        containerLayer = static_cast<ContainerLayer*>(oldLayer);
+        ResetLayerStateForRecycling(containerLayer);
+      }
+    }
+  }
+  if (!containerLayer) {
+    // No suitable existing layer was found.
+    containerLayer = aManager->CreateContainerLayer();
+    if (!containerLayer)
+      return nullptr;
+  }
+
+  LayerState state = aContainerItem ? aContainerItem->GetLayerState(aBuilder, aManager, aParameters) : LAYER_ACTIVE;
+  if (state == LAYER_INACTIVE &&
+      nsDisplayItem::ForceActiveLayers()) {
+    state = LAYER_ACTIVE;
+  }
+
+  if (aContainerItem && state == LAYER_ACTIVE_EMPTY) {
+    // Empty layers only have metadata and should never have display items. We
+    // early exit because later, invalidation will walk up the frame tree to
+    // determine which painted layer gets invalidated. Since an empty layer
+    // should never have anything to paint, it should never be invalidated.
+    NS_ASSERTION(aChildren->IsEmpty(), "Should have no children");
+    return containerLayer.forget();
+  }
+
+  const DisplayItemScrollClip* containerScrollClip = aParameters.mScrollClip;
+
+  ContainerLayerParameters scaleParameters;
+  nsRect bounds = aChildren->GetScrollClippedBoundsUpTo(aBuilder, containerScrollClip);
+  nsRect childrenVisible =
+      aContainerItem ? aContainerItem->GetVisibleRectForChildren() :
+          aContainerFrame->GetVisualOverflowRectRelativeToSelf();
+  if (!ChooseScaleAndSetTransform(this, aBuilder, aContainerFrame,
+                                  aContainerItem,
+                                  bounds.Intersect(childrenVisible),
+                                  aTransform, aParameters,
+                                  containerLayer, state, scaleParameters)) {
+    return nullptr;
+  }
+
+  uint32_t oldGeneration = mContainerLayerGeneration;
+  mContainerLayerGeneration = ++mMaxContainerLayerGeneration;
+
+  if (mRetainingManager) {
+    if (aContainerItem) {
+      StoreDataForFrame(aContainerItem, containerLayer, LAYER_ACTIVE);
+    } else {
+      StoreDataForFrame(aContainerFrame, containerDisplayItemKey, containerLayer, LAYER_ACTIVE);
+    }
+  }
+
+  LayerManagerData* data = static_cast<LayerManagerData*>
+    (aManager->GetUserData(&gLayerManagerUserData));
+
+  nsIntRect pixBounds;
+  nscoord appUnitsPerDevPixel;
+  bool flattenToSingleLayer = false;
+  if ((aContainerFrame->GetStateBits() & NS_FRAME_NO_COMPONENT_ALPHA) &&
+      mRetainingManager &&
+      mRetainingManager->ShouldAvoidComponentAlphaLayers() &&
+      !nsLayoutUtils::AsyncPanZoomEnabled(aContainerFrame))
+  {
+    flattenToSingleLayer = true;
+  }
+
+  nscolor backgroundColor = NS_RGBA(0,0,0,0);
+  if (aFlags & CONTAINER_ALLOW_PULL_BACKGROUND_COLOR) {
+    backgroundColor = aParameters.mBackgroundColor;
+  }
+
+  uint32_t flags;
+  while (true) {
+    ContainerState state(aBuilder, aManager, aManager->GetLayerBuilder(),
+                         aContainerFrame, aContainerItem, bounds,
+                         containerLayer, scaleParameters, flattenToSingleLayer,
+                         backgroundColor, containerScrollClip);
+
+    state.ProcessDisplayItems(aChildren);
+
+    // Set CONTENT_COMPONENT_ALPHA if any of our children have it.
+    // This is suboptimal ... a child could have text that's over transparent
+    // pixels in its own layer, but over opaque parts of previous siblings.
+    bool hasComponentAlphaChildren = false;
+    bool mayFlatten =
+      mRetainingManager &&
+      mRetainingManager->ShouldAvoidComponentAlphaLayers() &&
+      !flattenToSingleLayer &&
+      !nsLayoutUtils::AsyncPanZoomEnabled(aContainerFrame);
+
+    pixBounds = state.ScaleToOutsidePixels(bounds, false);
+    appUnitsPerDevPixel = state.GetAppUnitsPerDevPixel();
+    state.Finish(&flags, pixBounds, aChildren, mayFlatten ? &hasComponentAlphaChildren : nullptr);
+
+    if (hasComponentAlphaChildren &&
+        !(flags & Layer::CONTENT_DISABLE_FLATTENING) &&
+        containerLayer->HasMultipleChildren())
+    {
+      // Since we don't want any component alpha layers on BasicLayers, we repeat
+      // the layer building process with this explicitely forced off.
+      // We restore the previous FrameLayerBuilder state since the first set
+      // of layer building will have changed it.
+      flattenToSingleLayer = true;
+
+      // Restore DisplayItemData
+      for (auto iter = data->mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
+        DisplayItemData* data = iter.Get()->GetKey();
+        if (data->mUsed && data->mContainerLayerGeneration >= mContainerLayerGeneration) {
+          iter.Remove();
+        }
+      }
+
+      // Restore PaintedLayerItemEntries
+      for (auto iter = mPaintedLayerItems.Iter(); !iter.Done(); iter.Next()) {
+        PaintedLayerItemsEntry* entry = iter.Get();
+        if (entry->mContainerLayerGeneration >= mContainerLayerGeneration) {
+          // We can just remove these items rather than attempting to revert them
+          // because we're going to want to invalidate everything when transitioning
+          // to component alpha flattening.
+          iter.Remove();
+          continue;
+        }
+
+        for (uint32_t i = 0; i < entry->mItems.Length(); i++) {
+          if (entry->mItems[i].mContainerLayerGeneration >= mContainerLayerGeneration) {
+            entry->mItems.TruncateLength(i);
+            break;
+          }
+        }
+      }
+
+      aContainerFrame->AddStateBits(NS_FRAME_NO_COMPONENT_ALPHA);
+      continue;
+    }
+    break;
+  }
+
+  // CONTENT_COMPONENT_ALPHA is propogated up to the nearest CONTENT_OPAQUE
+  // ancestor so that BasicLayerManager knows when to copy the background into
+  // pushed groups. Accelerated layers managers can't necessarily do this (only
+  // when the visible region is a simple rect), so we propogate
+  // CONTENT_COMPONENT_ALPHA_DESCENDANT all the way to the root.
+  if (flags & Layer::CONTENT_COMPONENT_ALPHA) {
+    flags |= Layer::CONTENT_COMPONENT_ALPHA_DESCENDANT;
+  }
+
+  // Make sure that rounding the visible region out didn't add any area
+  // we won't paint
+  if (aChildren->IsOpaque() && !aChildren->NeedsTransparentSurface()) {
+    bounds.ScaleRoundIn(scaleParameters.mXScale, scaleParameters.mYScale);
+    if (bounds.Contains(ToAppUnits(pixBounds, appUnitsPerDevPixel))) {
+      // Clear CONTENT_COMPONENT_ALPHA and add CONTENT_OPAQUE instead.
+      flags &= ~Layer::CONTENT_COMPONENT_ALPHA;
+      flags |= Layer::CONTENT_OPAQUE;
+    }
+  }
+  containerLayer->SetContentFlags(flags);
+  // If aContainerItem is non-null some BuildContainerLayer further up the
+  // call stack is responsible for setting containerLayer's visible region.
+  if (!aContainerItem) {
+    containerLayer->SetVisibleRegion(LayerIntRegion::FromUnknownRegion(pixBounds));
+  }
+  if (aParameters.mLayerContentsVisibleRect) {
+    *aParameters.mLayerContentsVisibleRect = pixBounds + scaleParameters.mOffset;
+  }
+
+  mContainerLayerGeneration = oldGeneration;
+  nsPresContext::ClearNotifySubDocInvalidationData(containerLayer);
+
+  return containerLayer.forget();
+}
+
+Layer*
+FrameLayerBuilder::GetLeafLayerFor(nsDisplayListBuilder* aBuilder,
+                                   nsDisplayItem* aItem)
+{
+  Layer* layer = GetOldLayerFor(aItem);
+  if (!layer)
+    return nullptr;
+  if (layer->HasUserData(&gPaintedDisplayItemLayerUserData)) {
+    // This layer was created to render Thebes-rendered content for this
+    // display item. The display item should not use it for its own
+    // layer rendering.
+    return nullptr;
+  }
+  ResetLayerStateForRecycling(layer);
+  return layer;
+}
+
+/* static */ void
+FrameLayerBuilder::InvalidateAllLayers(LayerManager* aManager)
+{
+  LayerManagerData* data = static_cast<LayerManagerData*>
+    (aManager->GetUserData(&gLayerManagerUserData));
+  if (data) {
+    data->mInvalidateAllLayers = true;
+  }
+}
+
+/* static */ void
+FrameLayerBuilder::InvalidateAllLayersForFrame(nsIFrame *aFrame)
+{
+  const nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(LayerManagerDataProperty());
+  if (array) {
+    for (uint32_t i = 0; i < array->Length(); i++) {
+      AssertDisplayItemData(array->ElementAt(i))->mParent->mInvalidateAllLayers = true;
+    }
+  }
+}
+
+/* static */
+Layer*
+FrameLayerBuilder::GetDedicatedLayer(nsIFrame* aFrame, uint32_t aDisplayItemKey)
+{
+  //TODO: This isn't completely correct, since a frame could exist as a layer
+  // in the normal widget manager, and as a different layer (or no layer)
+  // in the secondary manager
+
+  const nsTArray<DisplayItemData*>* array =
+    aFrame->Properties().Get(LayerManagerDataProperty());
+  if (array) {
+    for (uint32_t i = 0; i < array->Length(); i++) {
+      DisplayItemData *element = AssertDisplayItemData(array->ElementAt(i));
+      if (!element->mParent->mLayerManager->IsWidgetLayerManager()) {
+        continue;
+      }
+      if (element->mDisplayItemKey == aDisplayItemKey) {
+        if (element->mOptLayer) {
+          return element->mOptLayer;
+        }
+
+        Layer* layer = element->mLayer;
+        if (!layer->HasUserData(&gColorLayerUserData) &&
+            !layer->HasUserData(&gImageLayerUserData) &&
+            !layer->HasUserData(&gPaintedDisplayItemLayerUserData)) {
+          return layer;
+        }
+      }
+    }
+  }
+  return nullptr;
+}
+
+static gfxSize
+PredictScaleForContent(nsIFrame* aFrame, nsIFrame* aAncestorWithScale,
+                       const gfxSize& aScale)
+{
+  Matrix4x4 transform = Matrix4x4::Scaling(aScale.width, aScale.height, 1.0);
+  if (aFrame != aAncestorWithScale) {
+    // aTransform is applied first, then the scale is applied to the result
+    transform = nsLayoutUtils::GetTransformToAncestor(aFrame, aAncestorWithScale)*transform;
+  }
+  Matrix transform2d;
+  if (transform.CanDraw2D(&transform2d)) {
+     return ThebesMatrix(transform2d).ScaleFactors(true);
+  }
+  return gfxSize(1.0, 1.0);
+}
+
+gfxSize
+FrameLayerBuilder::GetPaintedLayerScaleForFrame(nsIFrame* aFrame)
+{
+  MOZ_ASSERT(aFrame, "need a frame");
+  nsIFrame* last = nullptr;
+  for (nsIFrame* f = aFrame; f; f = nsLayoutUtils::GetCrossDocParentFrame(f)) {
+    last = f;
+
+    if (nsLayoutUtils::IsPopup(f)) {
+      // Don't examine ancestors of a popup. It won't make sense to check
+      // the transform from some content inside the popup to some content
+      // which is an ancestor of the popup.
+      break;
+    }
+
+    const nsTArray<DisplayItemData*>* array =
+      f->Properties().Get(LayerManagerDataProperty());
+    if (!array) {
+      continue;
+    }
+
+    for (uint32_t i = 0; i < array->Length(); i++) {
+      Layer* layer = AssertDisplayItemData(array->ElementAt(i))->mLayer;
+      ContainerLayer* container = layer->AsContainerLayer();
+      if (!container ||
+          !layer->Manager()->IsWidgetLayerManager()) {
+        continue;
+      }
+      for (Layer* l = container->GetFirstChild(); l; l = l->GetNextSibling()) {
+        PaintedDisplayItemLayerUserData* data =
+            static_cast<PaintedDisplayItemLayerUserData*>
+              (l->GetUserData(&gPaintedDisplayItemLayerUserData));
+        if (data) {
+          return PredictScaleForContent(aFrame, f, gfxSize(data->mXScale, data->mYScale));
+        }
+      }
+    }
+  }
+
+  float presShellResolution = last->PresContext()->PresShell()->GetResolution();
+  return PredictScaleForContent(aFrame, last,
+      gfxSize(presShellResolution, presShellResolution));
+}
+
+#ifdef MOZ_DUMP_PAINTING
+static void DebugPaintItem(DrawTarget& aDrawTarget,
+                           nsPresContext* aPresContext,
+                           nsDisplayItem *aItem,
+                           nsDisplayListBuilder* aBuilder)
+{
+  bool snap;
+  Rect bounds = NSRectToRect(aItem->GetBounds(aBuilder, &snap),
+                             aPresContext->AppUnitsPerDevPixel());
+
+  RefPtr<DrawTarget> tempDT =
+    aDrawTarget.CreateSimilarDrawTarget(IntSize::Truncate(bounds.width, bounds.height),
+                                        SurfaceFormat::B8G8R8A8);
+  RefPtr<gfxContext> context = gfxContext::CreateOrNull(tempDT);
+  if (!context) {
+    // Leave this as crash, it's in the debugging code, we want to know
+    gfxDevCrash(LogReason::InvalidContext) << "DebugPaintItem context problem " << gfx::hexa(tempDT);
+    return;
+  }
+  context->SetMatrix(gfxMatrix::Translation(-bounds.x, -bounds.y));
+  nsRenderingContext ctx(context);
+
+  aItem->Paint(aBuilder, &ctx);
+  RefPtr<SourceSurface> surface = tempDT->Snapshot();
+  DumpPaintedImage(aItem, surface);
+
+  aDrawTarget.DrawSurface(surface, bounds, Rect(Point(0,0), bounds.Size()));
+
+  aItem->SetPainted();
+}
+#endif
+
+/* static */ void
+FrameLayerBuilder::RecomputeVisibilityForItems(nsTArray<ClippedDisplayItem>& aItems,
+                                               nsDisplayListBuilder *aBuilder,
+                                               const nsIntRegion& aRegionToDraw,
+                                               const nsIntPoint& aOffset,
+                                               int32_t aAppUnitsPerDevPixel,
+                                               float aXScale,
+                                               float aYScale)
+{
+  uint32_t i;
+  // Update visible regions. We perform visibility analysis to take account
+  // of occlusion culling.
+  nsRegion visible = aRegionToDraw.ToAppUnits(aAppUnitsPerDevPixel);
+  visible.MoveBy(NSIntPixelsToAppUnits(aOffset.x, aAppUnitsPerDevPixel),
+                 NSIntPixelsToAppUnits(aOffset.y, aAppUnitsPerDevPixel));
+  visible.ScaleInverseRoundOut(aXScale, aYScale);
+
+  for (i = aItems.Length(); i > 0; --i) {
+    ClippedDisplayItem* cdi = &aItems[i - 1];
+    const DisplayItemClip& clip = cdi->mItem->GetClip();
+
+    NS_ASSERTION(AppUnitsPerDevPixel(cdi->mItem) == aAppUnitsPerDevPixel,
+                 "a painted layer should contain items only at the same zoom");
+
+    MOZ_ASSERT(clip.HasClip() || clip.GetRoundedRectCount() == 0,
+               "If we have rounded rects, we must have a clip rect");
+
+    if (!clip.IsRectAffectedByClip(visible.GetBounds())) {
+      cdi->mItem->RecomputeVisibility(aBuilder, &visible);
+      continue;
+    }
+
+    // Do a little dance to account for the fact that we're clipping
+    // to cdi->mClipRect
+    nsRegion clipped;
+    clipped.And(visible, clip.NonRoundedIntersection());
+    nsRegion finalClipped = clipped;
+    cdi->mItem->RecomputeVisibility(aBuilder, &finalClipped);
+    // If we have rounded clip rects, don't subtract from the visible
+    // region since we aren't displaying everything inside the rect.
+    if (clip.GetRoundedRectCount() == 0) {
+      nsRegion removed;
+      removed.Sub(clipped, finalClipped);
+      nsRegion newVisible;
+      newVisible.Sub(visible, removed);
+      // Don't let the visible region get too complex.
+      if (newVisible.GetNumRects() <= 15) {
+        visible = newVisible;
+      }
+    }
+  }
+}
+
+void
+FrameLayerBuilder::PaintItems(nsTArray<ClippedDisplayItem>& aItems,
+                              const nsIntRect& aRect,
+                              gfxContext *aContext,
+                              nsRenderingContext *aRC,
+                              nsDisplayListBuilder* aBuilder,
+                              nsPresContext* aPresContext,
+                              const nsIntPoint& aOffset,
+                              float aXScale, float aYScale,
+                              int32_t aCommonClipCount)
+{
+  DrawTarget& aDrawTarget = *aRC->GetDrawTarget();
+
+  int32_t appUnitsPerDevPixel = aPresContext->AppUnitsPerDevPixel();
+  nsRect boundRect = ToAppUnits(aRect, appUnitsPerDevPixel);
+  boundRect.MoveBy(NSIntPixelsToAppUnits(aOffset.x, appUnitsPerDevPixel),
+                 NSIntPixelsToAppUnits(aOffset.y, appUnitsPerDevPixel));
+  boundRect.ScaleInverseRoundOut(aXScale, aYScale);
+
+  DisplayItemClip currentClip;
+  bool currentClipIsSetInContext = false;
+  DisplayItemClip tmpClip;
+
+  for (uint32_t i = 0; i < aItems.Length(); ++i) {
+    ClippedDisplayItem* cdi = &aItems[i];
+
+    nsRect paintRect = cdi->mItem->GetVisibleRect().Intersect(boundRect);
+    if (paintRect.IsEmpty())
+      continue;
+
+#ifdef MOZ_DUMP_PAINTING
+    PROFILER_LABEL_PRINTF("DisplayList", "Draw",
+      js::ProfileEntry::Category::GRAPHICS, "%s", cdi->mItem->Name());
+#else
+    PROFILER_LABEL("DisplayList", "Draw",
+      js::ProfileEntry::Category::GRAPHICS);
+#endif
+
+    // If the new desired clip state is different from the current state,
+    // update the clip.
+    const DisplayItemClip* clip = &cdi->mItem->GetClip();
+    if (clip->GetRoundedRectCount() > 0 &&
+        !clip->IsRectClippedByRoundedCorner(cdi->mItem->GetVisibleRect())) {
+      tmpClip = *clip;
+      tmpClip.RemoveRoundedCorners();
+      clip = &tmpClip;
+    }
+    if (currentClipIsSetInContext != clip->HasClip() ||
+        (clip->HasClip() && *clip != currentClip)) {
+      if (currentClipIsSetInContext) {
+        aContext->Restore();
+      }
+      currentClipIsSetInContext = clip->HasClip();
+      if (currentClipIsSetInContext) {
+        currentClip = *clip;
+        aContext->Save();
+        NS_ASSERTION(aCommonClipCount < 100,
+          "Maybe you really do have more than a hundred clipping rounded rects, or maybe something has gone wrong.");
+        currentClip.ApplyTo(aContext, aPresContext, aCommonClipCount);
+        aContext->NewPath();
+      }
+    }
+
+    if (cdi->mInactiveLayerManager) {
+      bool saved = aDrawTarget.GetPermitSubpixelAA();
+      PaintInactiveLayer(aBuilder, cdi->mInactiveLayerManager, cdi->mItem, aContext, aRC);
+      aDrawTarget.SetPermitSubpixelAA(saved);
+    } else {
+      nsIFrame* frame = cdi->mItem->Frame();
+      if (aBuilder->IsPaintingToWindow()) {
+        frame->AddStateBits(NS_FRAME_PAINTED_THEBES);
+      }
+#ifdef MOZ_DUMP_PAINTING
+      if (gfxEnv::DumpPaintItems()) {
+        DebugPaintItem(aDrawTarget, aPresContext, cdi->mItem, aBuilder);
+      } else {
+#else
+      {
+#endif
+        cdi->mItem->Paint(aBuilder, aRC);
+      }
+    }
+
+    if (CheckDOMModified())
+      break;
+  }
+
+  if (currentClipIsSetInContext) {
+    aContext->Restore();
+  }
+}
+
+/**
+ * Returns true if it is preferred to draw the list of display
+ * items separately for each rect in the visible region rather
+ * than clipping to a complex region.
+ */
+static bool
+ShouldDrawRectsSeparately(DrawTarget* aDrawTarget, DrawRegionClip aClip)
+{
+  if (!gfxPrefs::LayoutPaintRectsSeparately() ||
+      aClip == DrawRegionClip::NONE) {
+    return false;
+  }
+
+  return !aDrawTarget->SupportsRegionClipping();
+}
+
+static void DrawForcedBackgroundColor(DrawTarget& aDrawTarget,
+                                      const IntRect& aBounds,
+                                      nscolor aBackgroundColor)
+{
+  if (NS_GET_A(aBackgroundColor) > 0) {
+    ColorPattern color(ToDeviceColor(aBackgroundColor));
+    aDrawTarget.FillRect(Rect(aBounds), color);
+  }
+}
+
+/*
+ * A note on residual transforms:
+ *
+ * In a transformed subtree we sometimes apply the PaintedLayer's
+ * "residual transform" when drawing content into the PaintedLayer.
+ * This is a translation by components in the range [-0.5,0.5) provided
+ * by the layer system; applying the residual transform followed by the
+ * transforms used by layer compositing ensures that the subpixel alignment
+ * of the content of the PaintedLayer exactly matches what it would be if
+ * we used cairo/Thebes to draw directly to the screen without going through
+ * retained layer buffers.
+ *
+ * The visible and valid regions of the PaintedLayer are computed without
+ * knowing the residual transform (because we don't know what the residual
+ * transform is going to be until we've built the layer tree!). So we have to
+ * consider whether content painted in the range [x, xmost) might be painted
+ * outside the visible region we computed for that content. The visible region
+ * would be [floor(x), ceil(xmost)). The content would be rendered at
+ * [x + r, xmost + r), where -0.5 <= r < 0.5. So some half-rendered pixels could
+ * indeed fall outside the computed visible region, which is not a big deal;
+ * similar issues already arise when we snap cliprects to nearest pixels.
+ * Note that if the rendering of the content is snapped to nearest pixels ---
+ * which it often is --- then the content is actually rendered at
+ * [snap(x + r), snap(xmost + r)). It turns out that floor(x) <= snap(x + r)
+ * and ceil(xmost) >= snap(xmost + r), so the rendering of snapped content
+ * always falls within the visible region we computed.
+ */
+
+/* static */ void
+FrameLayerBuilder::DrawPaintedLayer(PaintedLayer* aLayer,
+                                   gfxContext* aContext,
+                                   const nsIntRegion& aRegionToDraw,
+                                   const nsIntRegion& aDirtyRegion,
+                                   DrawRegionClip aClip,
+                                   const nsIntRegion& aRegionToInvalidate,
+                                   void* aCallbackData)
+{
+  DrawTarget& aDrawTarget = *aContext->GetDrawTarget();
+
+  PROFILER_LABEL("FrameLayerBuilder", "DrawPaintedLayer",
+    js::ProfileEntry::Category::GRAPHICS);
+
+  nsDisplayListBuilder* builder = static_cast<nsDisplayListBuilder*>
+    (aCallbackData);
+
+  FrameLayerBuilder *layerBuilder = aLayer->Manager()->GetLayerBuilder();
+  NS_ASSERTION(layerBuilder, "Unexpectedly null layer builder!");
+
+  if (layerBuilder->CheckDOMModified())
+    return;
+
+  PaintedLayerItemsEntry* entry = layerBuilder->mPaintedLayerItems.GetEntry(aLayer);
+  NS_ASSERTION(entry, "We shouldn't be drawing into a layer with no items!");
+  if (!entry->mContainerLayerFrame) {
+    return;
+  }
+
+
+  PaintedDisplayItemLayerUserData* userData =
+    static_cast<PaintedDisplayItemLayerUserData*>
+      (aLayer->GetUserData(&gPaintedDisplayItemLayerUserData));
+  NS_ASSERTION(userData, "where did our user data go?");
+
+  bool shouldDrawRectsSeparately =
+    ShouldDrawRectsSeparately(&aDrawTarget, aClip);
+
+  if (!shouldDrawRectsSeparately) {
+    if (aClip == DrawRegionClip::DRAW) {
+      gfxUtils::ClipToRegion(aContext, aRegionToDraw);
+    }
+
+    DrawForcedBackgroundColor(aDrawTarget, aRegionToDraw.GetBounds(),
+                              userData->mForcedBackgroundColor);
+  }
+
+  if (NS_GET_A(userData->mFontSmoothingBackgroundColor) > 0) {
+    aContext->SetFontSmoothingBackgroundColor(
+      Color::FromABGR(userData->mFontSmoothingBackgroundColor));
+  }
+
+  // make the origin of the context coincide with the origin of the
+  // PaintedLayer
+  gfxContextMatrixAutoSaveRestore saveMatrix(aContext);
+  nsIntPoint offset = GetTranslationForPaintedLayer(aLayer);
+  nsPresContext* presContext = entry->mContainerLayerFrame->PresContext();
+
+  if (!userData->mVisibilityComputedRegion.Contains(aDirtyRegion) &&
+      !layerBuilder->GetContainingPaintedLayerData()) {
+    // Recompute visibility of items in our PaintedLayer, if required. Note
+    // that this recomputes visibility for all descendants of our display
+    // items too, so there's no need to do this for the items in inactive
+    // PaintedLayers. If aDirtyRegion has not changed since the previous call
+    // then we can skip this.
+    int32_t appUnitsPerDevPixel = presContext->AppUnitsPerDevPixel();
+    RecomputeVisibilityForItems(entry->mItems, builder, aDirtyRegion,
+                                offset, appUnitsPerDevPixel,
+                                userData->mXScale, userData->mYScale);
+    userData->mVisibilityComputedRegion = aDirtyRegion;
+  }
+
+  nsRenderingContext rc(aContext);
+
+  if (shouldDrawRectsSeparately) {
+    for (auto iter = aRegionToDraw.RectIter(); !iter.Done(); iter.Next()) {
+      const nsIntRect& iterRect = iter.Get();
+      gfxContextAutoSaveRestore save(aContext);
+      aContext->NewPath();
+      aContext->Rectangle(ThebesRect(iterRect));
+      aContext->Clip();
+
+      DrawForcedBackgroundColor(aDrawTarget, iterRect,
+                                userData->mForcedBackgroundColor);
+
+      // Apply the residual transform if it has been enabled, to ensure that
+      // snapping when we draw into aContext exactly matches the ideal transform.
+      // See above for why this is OK.
+      aContext->SetMatrix(
+        aContext->CurrentMatrix().Translate(aLayer->GetResidualTranslation() - gfxPoint(offset.x, offset.y)).
+                                  Scale(userData->mXScale, userData->mYScale));
+
+      layerBuilder->PaintItems(entry->mItems, iterRect, aContext, &rc,
+                               builder, presContext,
+                               offset, userData->mXScale, userData->mYScale,
+                               entry->mCommonClipCount);
+      if (gfxPrefs::GfxLoggingPaintedPixelCountEnabled()) {
+        aLayer->Manager()->AddPaintedPixelCount(iterRect.Area());
+      }
+    }
+  } else {
+    // Apply the residual transform if it has been enabled, to ensure that
+    // snapping when we draw into aContext exactly matches the ideal transform.
+    // See above for why this is OK.
+    aContext->SetMatrix(
+      aContext->CurrentMatrix().Translate(aLayer->GetResidualTranslation() - gfxPoint(offset.x, offset.y)).
+                                Scale(userData->mXScale,userData->mYScale));
+
+    layerBuilder->PaintItems(entry->mItems, aRegionToDraw.GetBounds(), aContext, &rc,
+                             builder, presContext,
+                             offset, userData->mXScale, userData->mYScale,
+                             entry->mCommonClipCount);
+    if (gfxPrefs::GfxLoggingPaintedPixelCountEnabled()) {
+      aLayer->Manager()->AddPaintedPixelCount(
+        aRegionToDraw.GetBounds().Area());
+    }
+  }
+
+  aContext->SetFontSmoothingBackgroundColor(Color());
+
+  bool isActiveLayerManager = !aLayer->Manager()->IsInactiveLayerManager();
+
+  if (presContext->GetPaintFlashing() && isActiveLayerManager) {
+    gfxContextAutoSaveRestore save(aContext);
+    if (shouldDrawRectsSeparately) {
+      if (aClip == DrawRegionClip::DRAW) {
+        gfxUtils::ClipToRegion(aContext, aRegionToDraw);
+      }
+    }
+    FlashPaint(aContext);
+  }
+
+  if (presContext->GetDocShell() && isActiveLayerManager) {
+    nsDocShell* docShell = static_cast<nsDocShell*>(presContext->GetDocShell());
+    RefPtr<TimelineConsumers> timelines = TimelineConsumers::Get();
+
+    if (timelines && timelines->HasConsumer(docShell)) {
+      timelines->AddMarkerForDocShell(docShell, Move(
+        MakeUnique<LayerTimelineMarker>(aRegionToDraw)));
+    }
+  }
+
+  if (!aRegionToInvalidate.IsEmpty()) {
+    aLayer->AddInvalidRect(aRegionToInvalidate.GetBounds());
+  }
+}
+
+bool
+FrameLayerBuilder::CheckDOMModified()
+{
+  if (!mRootPresContext ||
+      mInitialDOMGeneration == mRootPresContext->GetDOMGeneration())
+    return false;
+  if (mDetectedDOMModification) {
+    // Don't spam the console with extra warnings
+    return true;
+  }
+  mDetectedDOMModification = true;
+  // Painting is not going to complete properly. There's not much
+  // we can do here though. Invalidating the window to get another repaint
+  // is likely to lead to an infinite repaint loop.
+  NS_WARNING("Detected DOM modification during paint, bailing out!");
+  return true;
+}
+
+/* static */ void
+FrameLayerBuilder::DumpRetainedLayerTree(LayerManager* aManager, std::stringstream& aStream, bool aDumpHtml)
+{
+  aManager->Dump(aStream, "", aDumpHtml);
+}
+
+nsDisplayItemGeometry*
+FrameLayerBuilder::GetMostRecentGeometry(nsDisplayItem* aItem)
+{
+  typedef nsTArray<DisplayItemData*> DataArray;
+
+  // Retrieve the array of DisplayItemData associated with our frame.
+  FrameProperties properties = aItem->Frame()->Properties();
+  const DataArray* dataArray =
+    properties.Get(LayerManagerDataProperty());
+  if (!dataArray) {
+    return nullptr;
+  }
+
+  // Find our display item data, if it exists, and return its geometry.
+  uint32_t itemPerFrameKey = aItem->GetPerFrameKey();
+  for (uint32_t i = 0; i < dataArray->Length(); i++) {
+    DisplayItemData* data = AssertDisplayItemData(dataArray->ElementAt(i));
+    if (data->GetDisplayItemKey() == itemPerFrameKey) {
+      return data->GetGeometry();
+    }
+  }
+
+  return nullptr;
+}
+
+gfx::Rect
+CalculateBounds(const nsTArray<DisplayItemClip::RoundedRect>& aRects, int32_t A2D)
+{
+  nsRect bounds = aRects[0].mRect;
+  for (uint32_t i = 1; i < aRects.Length(); ++i) {
+    bounds.UnionRect(bounds, aRects[i].mRect);
+   }
+
+  return gfx::ToRect(nsLayoutUtils::RectToGfxRect(bounds, A2D));
+}
+
+static void
+SetClipCount(PaintedDisplayItemLayerUserData* apaintedData,
+             uint32_t aClipCount)
+{
+  if (apaintedData) {
+    apaintedData->mMaskClipCount = aClipCount;
+  }
+}
+
+void
+ContainerState::SetupMaskLayer(Layer *aLayer,
+                               const DisplayItemClip& aClip,
+                               uint32_t aRoundedRectClipCount)
+{
+  // if the number of clips we are going to mask has decreased, then aLayer might have
+  // cached graphics which assume the existence of a soon-to-be non-existent mask layer
+  // in that case, invalidate the whole layer.
+  PaintedDisplayItemLayerUserData* paintedData = GetPaintedDisplayItemLayerUserData(aLayer);
+  if (paintedData &&
+      aRoundedRectClipCount < paintedData->mMaskClipCount) {
+    PaintedLayer* painted = aLayer->AsPaintedLayer();
+    painted->InvalidateRegion(painted->GetValidRegion().GetBounds());
+  }
+
+  // don't build an unnecessary mask
+  if (aClip.GetRoundedRectCount() == 0 ||
+      aRoundedRectClipCount == 0) {
+    SetClipCount(paintedData, 0);
+    return;
+  }
+
+  RefPtr<Layer> maskLayer =
+    CreateMaskLayer(aLayer, aClip, Nothing(), aRoundedRectClipCount);
+
+  if (!maskLayer) {
+    SetClipCount(paintedData, 0);
+    return;
+  }
+
+  aLayer->SetMaskLayer(maskLayer);
+  SetClipCount(paintedData, aRoundedRectClipCount);
+}
+
+already_AddRefed<Layer>
+ContainerState::CreateMaskLayer(Layer *aLayer,
+                               const DisplayItemClip& aClip,
+                               const Maybe<size_t>& aForAncestorMaskLayer,
+                               uint32_t aRoundedRectClipCount)
+{
+  // aLayer will never be the container layer created by an nsDisplayMask
+  // because nsDisplayMask propagates the DisplayItemClip to its contents
+  // and is not clipped itself.
+  // This assertion will fail if that ever stops being the case.
+  MOZ_ASSERT(!aLayer->GetUserData(&gCSSMaskLayerUserData),
+             "A layer contains round clips should not have css-mask on it.");
+
+  // check if we can re-use the mask layer
+  MaskLayerKey recycleKey(aLayer, aForAncestorMaskLayer);
+  RefPtr<ImageLayer> maskLayer =
+    CreateOrRecycleMaskImageLayerFor(recycleKey,
+      [](Layer* aMaskLayer)
+      {
+        aMaskLayer->SetUserData(&gMaskLayerUserData,
+                                new MaskLayerUserData());
+      }
+    );
+  MaskLayerUserData* userData = GetMaskLayerUserData(maskLayer);
+
+  int32_t A2D = mContainerFrame->PresContext()->AppUnitsPerDevPixel();
+  MaskLayerUserData newData(aClip, aRoundedRectClipCount, A2D, mParameters);
+  if (*userData == newData) {
+    return maskLayer.forget();
+  }
+
+  // calculate a more precise bounding rect
+  gfx::Rect boundingRect = CalculateBounds(newData.mRoundedClipRects,
+                                           newData.mAppUnitsPerDevPixel);
+  boundingRect.Scale(mParameters.mXScale, mParameters.mYScale);
+
+  uint32_t maxSize = mManager->GetMaxTextureSize();
+  NS_ASSERTION(maxSize > 0, "Invalid max texture size");
+#ifdef MOZ_GFX_OPTIMIZE_MOBILE
+  // Make mask image width aligned to 4. See Bug 1245552.
+  gfx::Size surfaceSize(std::min<gfx::Float>(GetAlignedStride<4>(NSToIntCeil(boundingRect.Width()), 1), maxSize),
+                        std::min<gfx::Float>(boundingRect.Height(), maxSize));
+#else
+  gfx::Size surfaceSize(std::min<gfx::Float>(boundingRect.Width(), maxSize),
+                        std::min<gfx::Float>(boundingRect.Height(), maxSize));
+#endif
+
+  // maskTransform is applied to the clip when it is painted into the mask (as a
+  // component of imageTransform), and its inverse used when the mask is used for
+  // masking.
+  // It is the transform from the masked layer's space to mask space
+  gfx::Matrix maskTransform =
+    Matrix::Scaling(surfaceSize.width / boundingRect.Width(),
+                    surfaceSize.height / boundingRect.Height());
+  if (surfaceSize.IsEmpty()) {
+    // Return early if we know that the size of this mask surface is empty.
+    return nullptr;
+  }
+
+  gfx::Point p = boundingRect.TopLeft();
+  maskTransform.PreTranslate(-p.x, -p.y);
+  // imageTransform is only used when the clip is painted to the mask
+  gfx::Matrix imageTransform = maskTransform;
+  imageTransform.PreScale(mParameters.mXScale, mParameters.mYScale);
+
+  nsAutoPtr<MaskLayerImageCache::MaskLayerImageKey> newKey(
+    new MaskLayerImageCache::MaskLayerImageKey());
+
+  // copy and transform the rounded rects
+  for (uint32_t i = 0; i < newData.mRoundedClipRects.Length(); ++i) {
+    newKey->mRoundedClipRects.AppendElement(
+      MaskLayerImageCache::PixelRoundedRect(newData.mRoundedClipRects[i],
+                                            mContainerFrame->PresContext()));
+    newKey->mRoundedClipRects[i].ScaleAndTranslate(imageTransform);
+  }
+  newKey->mForwarder = mManager->AsShadowForwarder();
+
+  const MaskLayerImageCache::MaskLayerImageKey* lookupKey = newKey;
+
+  // check to see if we can reuse a mask image
+  RefPtr<ImageContainer> container =
+    GetMaskLayerImageCache()->FindImageFor(&lookupKey);
+
+  if (!container) {
+    IntSize surfaceSizeInt(NSToIntCeil(surfaceSize.width),
+                           NSToIntCeil(surfaceSize.height));
+    // no existing mask image, so build a new one
+    MaskImageData imageData(surfaceSizeInt, mManager);
+    RefPtr<DrawTarget> dt = imageData.CreateDrawTarget();
+
+    // fail if we can't get the right surface
+    if (!dt || !dt->IsValid()) {
+      NS_WARNING("Could not create DrawTarget for mask layer.");
+      return nullptr;
+    }
+
+    RefPtr<gfxContext> context = gfxContext::CreateOrNull(dt);
+    MOZ_ASSERT(context); // already checked the draw target above
+    context->Multiply(ThebesMatrix(imageTransform));
+
+    // paint the clipping rects with alpha to create the mask
+    aClip.FillIntersectionOfRoundedRectClips(context,
+                                             Color(1.f, 1.f, 1.f, 1.f),
+                                             newData.mAppUnitsPerDevPixel,
+                                             0,
+                                             aRoundedRectClipCount);
+
+    // build the image and container
+    MOZ_ASSERT(aLayer->Manager() == mManager);
+    container = imageData.CreateImageAndImageContainer();
+    NS_ASSERTION(container, "Could not create image container for mask layer.");
+
+    if (!container) {
+      return nullptr;
+    }
+
+    GetMaskLayerImageCache()->PutImage(newKey.forget(), container);
+  }
+
+  maskLayer->SetContainer(container);
+
+  maskTransform.Invert();
+  Matrix4x4 matrix = Matrix4x4::From2D(maskTransform);
+  matrix.PreTranslate(mParameters.mOffset.x, mParameters.mOffset.y, 0);
+  maskLayer->SetBaseTransform(matrix);
+
+  // save the details of the clip in user data
+  *userData = Move(newData);
+  userData->mImageKey.Reset(lookupKey);
+
+  return maskLayer.forget();
+}
+
+} // namespace mozilla