Add m-esr52 at 52.6.0

1 files changed, 942 insertions, 0 deletions

diff --git a/gfx/layers/apz/util/APZCCallbackHelper.cpp b/gfx/layers/apz/util/APZCCallbackHelper.cpp
new file mode 100644
index 000000000..3f33a59e4
--- /dev/null
+++ b/gfx/layers/apz/util/APZCCallbackHelper.cpp
@@ -0,0 +1,942 @@
+/* -*- Mode: C++; tab-width: 2; 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 "APZCCallbackHelper.h"
+
+#include "TouchActionHelper.h"
+#include "gfxPlatform.h" // For gfxPlatform::UseTiling
+#include "gfxPrefs.h"
+#include "LayersLogging.h"  // For Stringify
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/TabParent.h"
+#include "mozilla/IntegerPrintfMacros.h"
+#include "mozilla/layers/LayerTransactionChild.h"
+#include "mozilla/layers/ShadowLayers.h"
+#include "mozilla/TouchEvents.h"
+#include "nsContentUtils.h"
+#include "nsContainerFrame.h"
+#include "nsIScrollableFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsIInterfaceRequestorUtils.h"
+#include "nsIContent.h"
+#include "nsIDocument.h"
+#include "nsIDOMWindow.h"
+#include "nsIDOMWindowUtils.h"
+#include "nsRefreshDriver.h"
+#include "nsString.h"
+#include "nsView.h"
+#include "Layers.h"
+
+#define APZCCH_LOG(...)
+// #define APZCCH_LOG(...) printf_stderr("APZCCH: " __VA_ARGS__)
+
+namespace mozilla {
+namespace layers {
+
+using dom::TabParent;
+
+uint64_t APZCCallbackHelper::sLastTargetAPZCNotificationInputBlock = uint64_t(-1);
+
+void
+APZCCallbackHelper::AdjustDisplayPortForScrollDelta(
+    mozilla::layers::FrameMetrics& aFrameMetrics,
+    const CSSPoint& aActualScrollOffset)
+{
+  // Correct the display-port by the difference between the requested scroll
+  // offset and the resulting scroll offset after setting the requested value.
+  ScreenPoint shift =
+      (aFrameMetrics.GetScrollOffset() - aActualScrollOffset) *
+      aFrameMetrics.DisplayportPixelsPerCSSPixel();
+  ScreenMargin margins = aFrameMetrics.GetDisplayPortMargins();
+  margins.left -= shift.x;
+  margins.right += shift.x;
+  margins.top -= shift.y;
+  margins.bottom += shift.y;
+  aFrameMetrics.SetDisplayPortMargins(margins);
+}
+
+static void
+RecenterDisplayPort(mozilla::layers::FrameMetrics& aFrameMetrics)
+{
+  ScreenMargin margins = aFrameMetrics.GetDisplayPortMargins();
+  margins.right = margins.left = margins.LeftRight() / 2;
+  margins.top = margins.bottom = margins.TopBottom() / 2;
+  aFrameMetrics.SetDisplayPortMargins(margins);
+}
+
+static CSSPoint
+ScrollFrameTo(nsIScrollableFrame* aFrame, const FrameMetrics& aMetrics, bool& aSuccessOut)
+{
+  aSuccessOut = false;
+  CSSPoint targetScrollPosition = aMetrics.GetScrollOffset();
+
+  if (!aFrame) {
+    return targetScrollPosition;
+  }
+
+  CSSPoint geckoScrollPosition = CSSPoint::FromAppUnits(aFrame->GetScrollPosition());
+
+  // If the repaint request was triggered due to a previous main-thread scroll
+  // offset update sent to the APZ, then we don't need to do another scroll here
+  // and we can just return.
+  if (!aMetrics.GetScrollOffsetUpdated()) {
+    return geckoScrollPosition;
+  }
+
+  // If the frame is overflow:hidden on a particular axis, we don't want to allow
+  // user-driven scroll on that axis. Simply set the scroll position on that axis
+  // to whatever it already is. Note that this will leave the APZ's async scroll
+  // position out of sync with the gecko scroll position, but APZ can deal with that
+  // (by design). Note also that when we run into this case, even if both axes
+  // have overflow:hidden, we want to set aSuccessOut to true, so that the displayport
+  // follows the async scroll position rather than the gecko scroll position.
+  if (aFrame->GetScrollbarStyles().mVertical == NS_STYLE_OVERFLOW_HIDDEN) {
+    targetScrollPosition.y = geckoScrollPosition.y;
+  }
+  if (aFrame->GetScrollbarStyles().mHorizontal == NS_STYLE_OVERFLOW_HIDDEN) {
+    targetScrollPosition.x = geckoScrollPosition.x;
+  }
+
+  // If the scrollable frame is currently in the middle of an async or smooth
+  // scroll then we don't want to interrupt it (see bug 961280).
+  // Also if the scrollable frame got a scroll request from a higher priority origin
+  // since the last layers update, then we don't want to push our scroll request
+  // because we'll clobber that one, which is bad.
+  bool scrollInProgress = APZCCallbackHelper::IsScrollInProgress(aFrame);
+  if (!scrollInProgress) {
+    aFrame->ScrollToCSSPixelsApproximate(targetScrollPosition, nsGkAtoms::apz);
+    geckoScrollPosition = CSSPoint::FromAppUnits(aFrame->GetScrollPosition());
+    aSuccessOut = true;
+  }
+  // Return the final scroll position after setting it so that anything that relies
+  // on it can have an accurate value. Note that even if we set it above re-querying it
+  // is a good idea because it may have gotten clamped or rounded.
+  return geckoScrollPosition;
+}
+
+/**
+ * Scroll the scroll frame associated with |aContent| to the scroll position
+ * requested in |aMetrics|.
+ * The scroll offset in |aMetrics| is updated to reflect the actual scroll
+ * position.
+ * The displayport stored in |aMetrics| and the callback-transform stored on
+ * the content are updated to reflect any difference between the requested
+ * and actual scroll positions.
+ */
+static void
+ScrollFrame(nsIContent* aContent,
+            FrameMetrics& aMetrics)
+{
+  // Scroll the window to the desired spot
+  nsIScrollableFrame* sf = nsLayoutUtils::FindScrollableFrameFor(aMetrics.GetScrollId());
+  if (sf) {
+    sf->ResetScrollInfoIfGeneration(aMetrics.GetScrollGeneration());
+    sf->SetScrollableByAPZ(!aMetrics.IsScrollInfoLayer());
+  }
+  bool scrollUpdated = false;
+  CSSPoint apzScrollOffset = aMetrics.GetScrollOffset();
+  CSSPoint actualScrollOffset = ScrollFrameTo(sf, aMetrics, scrollUpdated);
+
+  if (scrollUpdated) {
+    if (aMetrics.IsScrollInfoLayer()) {
+      // In cases where the APZ scroll offset is different from the content scroll
+      // offset, we want to interpret the margins as relative to the APZ scroll
+      // offset except when the frame is not scrollable by APZ. Therefore, if the
+      // layer is a scroll info layer, we leave the margins as-is and they will
+      // be interpreted as relative to the content scroll offset.
+      if (nsIFrame* frame = aContent->GetPrimaryFrame()) {
+        frame->SchedulePaint();
+      }
+    } else {
+      // Correct the display port due to the difference between mScrollOffset and the
+      // actual scroll offset.
+      APZCCallbackHelper::AdjustDisplayPortForScrollDelta(aMetrics, actualScrollOffset);
+    }
+  } else {
+    // For whatever reason we couldn't update the scroll offset on the scroll frame,
+    // which means the data APZ used for its displayport calculation is stale. Fall
+    // back to a sane default behaviour. Note that we don't tile-align the recentered
+    // displayport because tile-alignment depends on the scroll position, and the
+    // scroll position here is out of our control. See bug 966507 comment 21 for a
+    // more detailed explanation.
+    RecenterDisplayPort(aMetrics);
+  }
+
+  aMetrics.SetScrollOffset(actualScrollOffset);
+
+  // APZ transforms inputs assuming we applied the exact scroll offset it
+  // requested (|apzScrollOffset|). Since we may not have, record the difference
+  // between what APZ asked for and what we actually applied, and apply it to
+  // input events to compensate.
+  // Note that if the main-thread had a change in its scroll position, we don't
+  // want to record that difference here, because it can be large and throw off
+  // input events by a large amount. It is also going to be transient, because
+  // any main-thread scroll position change will be synced to APZ and we will
+  // get another repaint request when APZ confirms. In the interval while this
+  // is happening we can just leave the callback transform as it was.
+  bool mainThreadScrollChanged =
+    sf && sf->CurrentScrollGeneration() != aMetrics.GetScrollGeneration() && nsLayoutUtils::CanScrollOriginClobberApz(sf->LastScrollOrigin());
+  if (aContent && !mainThreadScrollChanged) {
+    CSSPoint scrollDelta = apzScrollOffset - actualScrollOffset;
+    aContent->SetProperty(nsGkAtoms::apzCallbackTransform, new CSSPoint(scrollDelta),
+                          nsINode::DeleteProperty<CSSPoint>);
+  }
+}
+
+static void
+SetDisplayPortMargins(nsIPresShell* aPresShell,
+                      nsIContent* aContent,
+                      const FrameMetrics& aMetrics)
+{
+  if (!aContent) {
+    return;
+  }
+
+  bool hadDisplayPort = nsLayoutUtils::HasDisplayPort(aContent);
+  ScreenMargin margins = aMetrics.GetDisplayPortMargins();
+  nsLayoutUtils::SetDisplayPortMargins(aContent, aPresShell, margins, 0);
+  if (!hadDisplayPort) {
+    nsLayoutUtils::SetZeroMarginDisplayPortOnAsyncScrollableAncestors(
+        aContent->GetPrimaryFrame(), nsLayoutUtils::RepaintMode::Repaint);
+  }
+
+  CSSRect baseCSS = aMetrics.CalculateCompositedRectInCssPixels();
+  nsRect base(0, 0,
+              baseCSS.width * nsPresContext::AppUnitsPerCSSPixel(),
+              baseCSS.height * nsPresContext::AppUnitsPerCSSPixel());
+  nsLayoutUtils::SetDisplayPortBaseIfNotSet(aContent, base);
+}
+
+static already_AddRefed<nsIPresShell>
+GetPresShell(const nsIContent* aContent)
+{
+  nsCOMPtr<nsIPresShell> result;
+  if (nsIDocument* doc = aContent->GetComposedDoc()) {
+    result = doc->GetShell();
+  }
+  return result.forget();
+}
+
+static void
+SetPaintRequestTime(nsIContent* aContent, const TimeStamp& aPaintRequestTime)
+{
+  aContent->SetProperty(nsGkAtoms::paintRequestTime,
+                        new TimeStamp(aPaintRequestTime),
+                        nsINode::DeleteProperty<TimeStamp>);
+}
+
+void
+APZCCallbackHelper::UpdateRootFrame(FrameMetrics& aMetrics)
+{
+  if (aMetrics.GetScrollId() == FrameMetrics::NULL_SCROLL_ID) {
+    return;
+  }
+  nsIContent* content = nsLayoutUtils::FindContentFor(aMetrics.GetScrollId());
+  if (!content) {
+    return;
+  }
+
+  nsCOMPtr<nsIPresShell> shell = GetPresShell(content);
+  if (!shell || aMetrics.GetPresShellId() != shell->GetPresShellId()) {
+    return;
+  }
+
+  MOZ_ASSERT(aMetrics.GetUseDisplayPortMargins());
+
+  if (gfxPrefs::APZAllowZooming()) {
+    // If zooming is disabled then we don't really want to let APZ fiddle
+    // with these things. In theory setting the resolution here should be a
+    // no-op, but setting the SPCSPS is bad because it can cause a stale value
+    // to be returned by window.innerWidth/innerHeight (see bug 1187792).
+
+    float presShellResolution = shell->GetResolution();
+
+    // If the pres shell resolution has changed on the content side side
+    // the time this repaint request was fired, consider this request out of date
+    // and drop it; setting a zoom based on the out-of-date resolution can have
+    // the effect of getting us stuck with the stale resolution.
+    if (!FuzzyEqualsMultiplicative(presShellResolution, aMetrics.GetPresShellResolution())) {
+      return;
+    }
+
+    // The pres shell resolution is updated by the the async zoom since the
+    // last paint.
+    presShellResolution = aMetrics.GetPresShellResolution()
+                        * aMetrics.GetAsyncZoom().scale;
+    shell->SetResolutionAndScaleTo(presShellResolution);
+  }
+
+  // Do this as late as possible since scrolling can flush layout. It also
+  // adjusts the display port margins, so do it before we set those.
+  ScrollFrame(content, aMetrics);
+
+  SetDisplayPortMargins(shell, content, aMetrics);
+  SetPaintRequestTime(content, aMetrics.GetPaintRequestTime());
+}
+
+void
+APZCCallbackHelper::UpdateSubFrame(FrameMetrics& aMetrics)
+{
+  if (aMetrics.GetScrollId() == FrameMetrics::NULL_SCROLL_ID) {
+    return;
+  }
+  nsIContent* content = nsLayoutUtils::FindContentFor(aMetrics.GetScrollId());
+  if (!content) {
+    return;
+  }
+
+  MOZ_ASSERT(aMetrics.GetUseDisplayPortMargins());
+
+  // We don't currently support zooming for subframes, so nothing extra
+  // needs to be done beyond the tasks common to this and UpdateRootFrame.
+  ScrollFrame(content, aMetrics);
+  if (nsCOMPtr<nsIPresShell> shell = GetPresShell(content)) {
+    SetDisplayPortMargins(shell, content, aMetrics);
+  }
+  SetPaintRequestTime(content, aMetrics.GetPaintRequestTime());
+}
+
+bool
+APZCCallbackHelper::GetOrCreateScrollIdentifiers(nsIContent* aContent,
+                                                 uint32_t* aPresShellIdOut,
+                                                 FrameMetrics::ViewID* aViewIdOut)
+{
+    if (!aContent) {
+      return false;
+    }
+    *aViewIdOut = nsLayoutUtils::FindOrCreateIDFor(aContent);
+    if (nsCOMPtr<nsIPresShell> shell = GetPresShell(aContent)) {
+      *aPresShellIdOut = shell->GetPresShellId();
+      return true;
+    }
+    return false;
+}
+
+void
+APZCCallbackHelper::InitializeRootDisplayport(nsIPresShell* aPresShell)
+{
+  // Create a view-id and set a zero-margin displayport for the root element
+  // of the root document in the chrome process. This ensures that the scroll
+  // frame for this element gets an APZC, which in turn ensures that all content
+  // in the chrome processes is covered by an APZC.
+  // The displayport is zero-margin because this element is generally not
+  // actually scrollable (if it is, APZC will set proper margins when it's
+  // scrolled).
+  if (!aPresShell) {
+    return;
+  }
+
+  MOZ_ASSERT(aPresShell->GetDocument());
+  nsIContent* content = aPresShell->GetDocument()->GetDocumentElement();
+  if (!content) {
+    return;
+  }
+
+  uint32_t presShellId;
+  FrameMetrics::ViewID viewId;
+  if (APZCCallbackHelper::GetOrCreateScrollIdentifiers(content, &presShellId, &viewId)) {
+    // Note that the base rect that goes with these margins is set in
+    // nsRootBoxFrame::BuildDisplayList.
+    nsLayoutUtils::SetDisplayPortMargins(content, aPresShell, ScreenMargin(), 0,
+        nsLayoutUtils::RepaintMode::DoNotRepaint);
+    nsLayoutUtils::SetZeroMarginDisplayPortOnAsyncScrollableAncestors(
+        content->GetPrimaryFrame(), nsLayoutUtils::RepaintMode::DoNotRepaint);
+  }
+}
+
+nsPresContext*
+APZCCallbackHelper::GetPresContextForContent(nsIContent* aContent)
+{
+  nsIDocument* doc = aContent->GetComposedDoc();
+  if (!doc) {
+      return nullptr;
+  }
+  nsIPresShell* shell = doc->GetShell();
+  if (!shell) {
+      return nullptr;
+  }
+  return shell->GetPresContext();
+}
+
+nsIPresShell*
+APZCCallbackHelper::GetRootContentDocumentPresShellForContent(nsIContent* aContent)
+{
+    nsPresContext* context = GetPresContextForContent(aContent);
+    if (!context) {
+        return nullptr;
+    }
+    context = context->GetToplevelContentDocumentPresContext();
+    if (!context) {
+        return nullptr;
+    }
+    return context->PresShell();
+}
+
+static nsIPresShell*
+GetRootDocumentPresShell(nsIContent* aContent)
+{
+    nsIDocument* doc = aContent->GetComposedDoc();
+    if (!doc) {
+        return nullptr;
+    }
+    nsIPresShell* shell = doc->GetShell();
+    if (!shell) {
+        return nullptr;
+    }
+    nsPresContext* context = shell->GetPresContext();
+    if (!context) {
+        return nullptr;
+    }
+    context = context->GetRootPresContext();
+    if (!context) {
+        return nullptr;
+    }
+    return context->PresShell();
+}
+
+CSSPoint
+APZCCallbackHelper::ApplyCallbackTransform(const CSSPoint& aInput,
+                                           const ScrollableLayerGuid& aGuid)
+{
+    CSSPoint input = aInput;
+    if (aGuid.mScrollId == FrameMetrics::NULL_SCROLL_ID) {
+        return input;
+    }
+    nsCOMPtr<nsIContent> content = nsLayoutUtils::FindContentFor(aGuid.mScrollId);
+    if (!content) {
+        return input;
+    }
+
+    // First, scale inversely by the root content document's pres shell
+    // resolution to cancel the scale-to-resolution transform that the
+    // compositor adds to the layer with the pres shell resolution. The points
+    // sent to Gecko by APZ don't have this transform unapplied (unlike other
+    // compositor-side transforms) because APZ doesn't know about it.
+    if (nsIPresShell* shell = GetRootDocumentPresShell(content)) {
+        input = input / shell->GetResolution();
+    }
+
+    // This represents any resolution on the Root Content Document (RCD)
+    // that's not on the Root Document (RD). That is, on platforms where
+    // RCD == RD, it's 1, and on platforms where RCD != RD, it's the RCD
+    // resolution. 'input' has this resolution applied, but the scroll
+    // delta retrieved below do not, so we need to apply them to the
+    // delta before adding the delta to 'input'. (Technically, deltas
+    // from scroll frames outside the RCD would already have this
+    // resolution applied, but we don't have such scroll frames in
+    // practice.)
+    float nonRootResolution = 1.0f;
+    if (nsIPresShell* shell = GetRootContentDocumentPresShellForContent(content)) {
+      nonRootResolution = shell->GetCumulativeNonRootScaleResolution();
+    }
+    // Now apply the callback-transform. This is only approximately correct,
+    // see the comment on GetCumulativeApzCallbackTransform for details.
+    CSSPoint transform = nsLayoutUtils::GetCumulativeApzCallbackTransform(content->GetPrimaryFrame());
+    return input + transform * nonRootResolution;
+}
+
+LayoutDeviceIntPoint
+APZCCallbackHelper::ApplyCallbackTransform(const LayoutDeviceIntPoint& aPoint,
+                                           const ScrollableLayerGuid& aGuid,
+                                           const CSSToLayoutDeviceScale& aScale)
+{
+    LayoutDevicePoint point = LayoutDevicePoint(aPoint.x, aPoint.y);
+    point = ApplyCallbackTransform(point / aScale, aGuid) * aScale;
+    return LayoutDeviceIntPoint::Round(point);
+}
+
+void
+APZCCallbackHelper::ApplyCallbackTransform(WidgetEvent& aEvent,
+                                           const ScrollableLayerGuid& aGuid,
+                                           const CSSToLayoutDeviceScale& aScale)
+{
+  if (aEvent.AsTouchEvent()) {
+    WidgetTouchEvent& event = *(aEvent.AsTouchEvent());
+    for (size_t i = 0; i < event.mTouches.Length(); i++) {
+      event.mTouches[i]->mRefPoint = ApplyCallbackTransform(
+          event.mTouches[i]->mRefPoint, aGuid, aScale);
+    }
+  } else {
+    aEvent.mRefPoint = ApplyCallbackTransform(aEvent.mRefPoint, aGuid, aScale);
+  }
+}
+
+nsEventStatus
+APZCCallbackHelper::DispatchWidgetEvent(WidgetGUIEvent& aEvent)
+{
+  nsEventStatus status = nsEventStatus_eConsumeNoDefault;
+  if (aEvent.mWidget) {
+    aEvent.mWidget->DispatchEvent(&aEvent, status);
+  }
+  return status;
+}
+
+nsEventStatus
+APZCCallbackHelper::DispatchSynthesizedMouseEvent(EventMessage aMsg,
+                                                  uint64_t aTime,
+                                                  const LayoutDevicePoint& aRefPoint,
+                                                  Modifiers aModifiers,
+                                                  int32_t aClickCount,
+                                                  nsIWidget* aWidget)
+{
+  MOZ_ASSERT(aMsg == eMouseMove || aMsg == eMouseDown ||
+             aMsg == eMouseUp || aMsg == eMouseLongTap);
+
+  WidgetMouseEvent event(true, aMsg, aWidget,
+                         WidgetMouseEvent::eReal, WidgetMouseEvent::eNormal);
+  event.mRefPoint = LayoutDeviceIntPoint::Truncate(aRefPoint.x, aRefPoint.y);
+  event.mTime = aTime;
+  event.button = WidgetMouseEvent::eLeftButton;
+  event.inputSource = nsIDOMMouseEvent::MOZ_SOURCE_TOUCH;
+  if (aMsg == eMouseLongTap) {
+    event.mFlags.mOnlyChromeDispatch = true;
+  }
+  event.mIgnoreRootScrollFrame = true;
+  if (aMsg != eMouseMove) {
+    event.mClickCount = aClickCount;
+  }
+  event.mModifiers = aModifiers;
+  // Real touch events will generate corresponding pointer events. We set
+  // convertToPointer to false to prevent the synthesized mouse events generate
+  // pointer events again.
+  event.convertToPointer = false;
+  return DispatchWidgetEvent(event);
+}
+
+bool
+APZCCallbackHelper::DispatchMouseEvent(const nsCOMPtr<nsIPresShell>& aPresShell,
+                                       const nsString& aType,
+                                       const CSSPoint& aPoint,
+                                       int32_t aButton,
+                                       int32_t aClickCount,
+                                       int32_t aModifiers,
+                                       bool aIgnoreRootScrollFrame,
+                                       unsigned short aInputSourceArg)
+{
+  NS_ENSURE_TRUE(aPresShell, true);
+
+  bool defaultPrevented = false;
+  nsContentUtils::SendMouseEvent(aPresShell, aType, aPoint.x, aPoint.y,
+      aButton, nsIDOMWindowUtils::MOUSE_BUTTONS_NOT_SPECIFIED, aClickCount,
+      aModifiers, aIgnoreRootScrollFrame, 0, aInputSourceArg, false,
+      &defaultPrevented, false, /* aIsWidgetEventSynthesized = */ false);
+  return defaultPrevented;
+}
+
+
+void
+APZCCallbackHelper::FireSingleTapEvent(const LayoutDevicePoint& aPoint,
+                                       Modifiers aModifiers,
+                                       int32_t aClickCount,
+                                       nsIWidget* aWidget)
+{
+  if (aWidget->Destroyed()) {
+    return;
+  }
+  APZCCH_LOG("Dispatching single-tap component events to %s\n",
+    Stringify(aPoint).c_str());
+  int time = 0;
+  DispatchSynthesizedMouseEvent(eMouseMove, time, aPoint, aModifiers, aClickCount, aWidget);
+  DispatchSynthesizedMouseEvent(eMouseDown, time, aPoint, aModifiers, aClickCount, aWidget);
+  DispatchSynthesizedMouseEvent(eMouseUp, time, aPoint, aModifiers, aClickCount, aWidget);
+}
+
+static dom::Element*
+GetDisplayportElementFor(nsIScrollableFrame* aScrollableFrame)
+{
+  if (!aScrollableFrame) {
+    return nullptr;
+  }
+  nsIFrame* scrolledFrame = aScrollableFrame->GetScrolledFrame();
+  if (!scrolledFrame) {
+    return nullptr;
+  }
+  // |scrolledFrame| should at this point be the root content frame of the
+  // nearest ancestor scrollable frame. The element corresponding to this
+  // frame should be the one with the displayport set on it, so find that
+  // element and return it.
+  nsIContent* content = scrolledFrame->GetContent();
+  MOZ_ASSERT(content->IsElement()); // roc says this must be true
+  return content->AsElement();
+}
+
+
+static dom::Element*
+GetRootDocumentElementFor(nsIWidget* aWidget)
+{
+  // This returns the root element that ChromeProcessController sets the
+  // displayport on during initialization.
+  if (nsView* view = nsView::GetViewFor(aWidget)) {
+    if (nsIPresShell* shell = view->GetPresShell()) {
+      MOZ_ASSERT(shell->GetDocument());
+      return shell->GetDocument()->GetDocumentElement();
+    }
+  }
+  return nullptr;
+}
+
+static nsIFrame*
+UpdateRootFrameForTouchTargetDocument(nsIFrame* aRootFrame)
+{
+#if defined(MOZ_WIDGET_ANDROID)
+  // Re-target so that the hit test is performed relative to the frame for the
+  // Root Content Document instead of the Root Document which are different in
+  // Android. See bug 1229752 comment 16 for an explanation of why this is necessary.
+  if (nsIDocument* doc = aRootFrame->PresContext()->PresShell()->GetTouchEventTargetDocument()) {
+    if (nsIPresShell* shell = doc->GetShell()) {
+      if (nsIFrame* frame = shell->GetRootFrame()) {
+        return frame;
+      }
+    }
+  }
+#endif
+  return aRootFrame;
+}
+
+// Determine the scrollable target frame for the given point and add it to
+// the target list. If the frame doesn't have a displayport, set one.
+// Return whether or not a displayport was set.
+static bool
+PrepareForSetTargetAPZCNotification(nsIWidget* aWidget,
+                                    const ScrollableLayerGuid& aGuid,
+                                    nsIFrame* aRootFrame,
+                                    const LayoutDeviceIntPoint& aRefPoint,
+                                    nsTArray<ScrollableLayerGuid>* aTargets)
+{
+  ScrollableLayerGuid guid(aGuid.mLayersId, 0, FrameMetrics::NULL_SCROLL_ID);
+  nsPoint point =
+    nsLayoutUtils::GetEventCoordinatesRelativeTo(aWidget, aRefPoint, aRootFrame);
+  nsIFrame* target =
+    nsLayoutUtils::GetFrameForPoint(aRootFrame, point, nsLayoutUtils::IGNORE_ROOT_SCROLL_FRAME);
+  nsIScrollableFrame* scrollAncestor = target
+    ? nsLayoutUtils::GetAsyncScrollableAncestorFrame(target)
+    : aRootFrame->PresContext()->PresShell()->GetRootScrollFrameAsScrollable();
+
+  // Assuming that if there's no scrollAncestor, there's already a displayPort.
+  nsCOMPtr<dom::Element> dpElement = scrollAncestor
+    ? GetDisplayportElementFor(scrollAncestor)
+    : GetRootDocumentElementFor(aWidget);
+
+  nsAutoString dpElementDesc;
+  if (dpElement) {
+    dpElement->Describe(dpElementDesc);
+  }
+  APZCCH_LOG("For event at %s found scrollable element %p (%s)\n",
+      Stringify(aRefPoint).c_str(), dpElement.get(),
+      NS_LossyConvertUTF16toASCII(dpElementDesc).get());
+
+  bool guidIsValid = APZCCallbackHelper::GetOrCreateScrollIdentifiers(
+    dpElement, &(guid.mPresShellId), &(guid.mScrollId));
+  aTargets->AppendElement(guid);
+
+  if (!guidIsValid || nsLayoutUtils::HasDisplayPort(dpElement)) {
+    return false;
+  }
+
+  if (!scrollAncestor) {
+    MOZ_ASSERT(false);  // If you hit this, please file a bug with STR.
+
+    // Attempt some sort of graceful handling based on a theory as to why we
+    // reach this point...
+    // If we get here, the document element is non-null, valid, but doesn't have
+    // a displayport. It's possible that the init code in ChromeProcessController
+    // failed for some reason, or the document element got swapped out at some
+    // later time. In this case let's try to set a displayport on the document
+    // element again and bail out on this operation.
+    APZCCH_LOG("Widget %p's document element %p didn't have a displayport\n",
+        aWidget, dpElement.get());
+    APZCCallbackHelper::InitializeRootDisplayport(aRootFrame->PresContext()->PresShell());
+    return false;
+  }
+
+  APZCCH_LOG("%p didn't have a displayport, so setting one...\n", dpElement.get());
+  bool activated = nsLayoutUtils::CalculateAndSetDisplayPortMargins(
+      scrollAncestor, nsLayoutUtils::RepaintMode::Repaint);
+  if (!activated) {
+    return false;
+  }
+
+  nsIFrame* frame = do_QueryFrame(scrollAncestor);
+  nsLayoutUtils::SetZeroMarginDisplayPortOnAsyncScrollableAncestors(frame,
+    nsLayoutUtils::RepaintMode::Repaint);
+
+  return true;
+}
+
+static void
+SendLayersDependentApzcTargetConfirmation(nsIPresShell* aShell, uint64_t aInputBlockId,
+                                          const nsTArray<ScrollableLayerGuid>& aTargets)
+{
+  LayerManager* lm = aShell->GetLayerManager();
+  if (!lm) {
+    return;
+  }
+
+  LayerTransactionChild* shadow = lm->AsShadowForwarder()->GetShadowManager();
+  if (!shadow) {
+    return;
+  }
+
+  shadow->SendSetConfirmedTargetAPZC(aInputBlockId, aTargets);
+}
+
+class DisplayportSetListener : public nsAPostRefreshObserver {
+public:
+  DisplayportSetListener(nsIPresShell* aPresShell,
+                         const uint64_t& aInputBlockId,
+                         const nsTArray<ScrollableLayerGuid>& aTargets)
+    : mPresShell(aPresShell)
+    , mInputBlockId(aInputBlockId)
+    , mTargets(aTargets)
+  {
+  }
+
+  virtual ~DisplayportSetListener()
+  {
+  }
+
+  void DidRefresh() override {
+    if (!mPresShell) {
+      MOZ_ASSERT_UNREACHABLE("Post-refresh observer fired again after failed attempt at unregistering it");
+      return;
+    }
+
+    APZCCH_LOG("Got refresh, sending target APZCs for input block %" PRIu64 "\n", mInputBlockId);
+    SendLayersDependentApzcTargetConfirmation(mPresShell, mInputBlockId, Move(mTargets));
+
+    if (!mPresShell->RemovePostRefreshObserver(this)) {
+      MOZ_ASSERT_UNREACHABLE("Unable to unregister post-refresh observer! Leaking it instead of leaving garbage registered");
+      // Graceful handling, just in case...
+      mPresShell = nullptr;
+      return;
+    }
+
+    delete this;
+  }
+
+private:
+  RefPtr<nsIPresShell> mPresShell;
+  uint64_t mInputBlockId;
+  nsTArray<ScrollableLayerGuid> mTargets;
+};
+
+// Sends a SetTarget notification for APZC, given one or more previous
+// calls to PrepareForAPZCSetTargetNotification().
+static void
+SendSetTargetAPZCNotificationHelper(nsIWidget* aWidget,
+                                    nsIPresShell* aShell,
+                                    const uint64_t& aInputBlockId,
+                                    const nsTArray<ScrollableLayerGuid>& aTargets,
+                                    bool aWaitForRefresh)
+{
+  bool waitForRefresh = aWaitForRefresh;
+  if (waitForRefresh) {
+    APZCCH_LOG("At least one target got a new displayport, need to wait for refresh\n");
+    waitForRefresh = aShell->AddPostRefreshObserver(
+      new DisplayportSetListener(aShell, aInputBlockId, Move(aTargets)));
+  }
+  if (!waitForRefresh) {
+    APZCCH_LOG("Sending target APZCs for input block %" PRIu64 "\n", aInputBlockId);
+    aWidget->SetConfirmedTargetAPZC(aInputBlockId, aTargets);
+  } else {
+    APZCCH_LOG("Successfully registered post-refresh observer\n");
+  }
+}
+
+void
+APZCCallbackHelper::SendSetTargetAPZCNotification(nsIWidget* aWidget,
+                                                  nsIDocument* aDocument,
+                                                  const WidgetGUIEvent& aEvent,
+                                                  const ScrollableLayerGuid& aGuid,
+                                                  uint64_t aInputBlockId)
+{
+  if (!aWidget || !aDocument) {
+    return;
+  }
+  if (aInputBlockId == sLastTargetAPZCNotificationInputBlock) {
+    // We have already confirmed the target APZC for a previous event of this
+    // input block. If we activated a scroll frame for this input block,
+    // sending another target APZC confirmation would be harmful, as it might
+    // race the original confirmation (which needs to go through a layers
+    // transaction).
+    APZCCH_LOG("Not resending target APZC confirmation for input block %" PRIu64 "\n", aInputBlockId);
+    return;
+  }
+  sLastTargetAPZCNotificationInputBlock = aInputBlockId;
+  if (nsIPresShell* shell = aDocument->GetShell()) {
+    if (nsIFrame* rootFrame = shell->GetRootFrame()) {
+      rootFrame = UpdateRootFrameForTouchTargetDocument(rootFrame);
+
+      bool waitForRefresh = false;
+      nsTArray<ScrollableLayerGuid> targets;
+
+      if (const WidgetTouchEvent* touchEvent = aEvent.AsTouchEvent()) {
+        for (size_t i = 0; i < touchEvent->mTouches.Length(); i++) {
+          waitForRefresh |= PrepareForSetTargetAPZCNotification(aWidget, aGuid,
+              rootFrame, touchEvent->mTouches[i]->mRefPoint, &targets);
+        }
+      } else if (const WidgetWheelEvent* wheelEvent = aEvent.AsWheelEvent()) {
+        waitForRefresh = PrepareForSetTargetAPZCNotification(aWidget, aGuid,
+            rootFrame, wheelEvent->mRefPoint, &targets);
+      } else if (const WidgetMouseEvent* mouseEvent = aEvent.AsMouseEvent()) {
+        waitForRefresh = PrepareForSetTargetAPZCNotification(aWidget, aGuid,
+            rootFrame, mouseEvent->mRefPoint, &targets);
+      }
+      // TODO: Do other types of events need to be handled?
+
+      if (!targets.IsEmpty()) {
+        SendSetTargetAPZCNotificationHelper(
+          aWidget,
+          shell,
+          aInputBlockId,
+          Move(targets),
+          waitForRefresh);
+      }
+    }
+  }
+}
+
+void
+APZCCallbackHelper::SendSetAllowedTouchBehaviorNotification(
+        nsIWidget* aWidget,
+        nsIDocument* aDocument,
+        const WidgetTouchEvent& aEvent,
+        uint64_t aInputBlockId,
+        const SetAllowedTouchBehaviorCallback& aCallback)
+{
+  if (nsIPresShell* shell = aDocument->GetShell()) {
+    if (nsIFrame* rootFrame = shell->GetRootFrame()) {
+      rootFrame = UpdateRootFrameForTouchTargetDocument(rootFrame);
+
+      nsTArray<TouchBehaviorFlags> flags;
+      for (uint32_t i = 0; i < aEvent.mTouches.Length(); i++) {
+        flags.AppendElement(
+          TouchActionHelper::GetAllowedTouchBehavior(aWidget,
+                rootFrame, aEvent.mTouches[i]->mRefPoint));
+      }
+      aCallback(aInputBlockId, Move(flags));
+    }
+  }
+}
+
+void
+APZCCallbackHelper::NotifyMozMouseScrollEvent(const FrameMetrics::ViewID& aScrollId, const nsString& aEvent)
+{
+  nsCOMPtr<nsIContent> targetContent = nsLayoutUtils::FindContentFor(aScrollId);
+  if (!targetContent) {
+    return;
+  }
+  nsCOMPtr<nsIDocument> ownerDoc = targetContent->OwnerDoc();
+  if (!ownerDoc) {
+    return;
+  }
+
+  nsContentUtils::DispatchTrustedEvent(
+    ownerDoc, targetContent,
+    aEvent,
+    true, true);
+}
+
+void
+APZCCallbackHelper::NotifyFlushComplete(nsIPresShell* aShell)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  // In some cases, flushing the APZ state to the main thread doesn't actually
+  // trigger a flush and repaint (this is an intentional optimization - the stuff
+  // visible to the user is still correct). However, reftests update their
+  // snapshot based on invalidation events that are emitted during paints,
+  // so we ensure that we kick off a paint when an APZ flush is done. Note that
+  // only chrome/testing code can trigger this behaviour.
+  if (aShell && aShell->GetRootFrame()) {
+    aShell->GetRootFrame()->SchedulePaint();
+  }
+
+  nsCOMPtr<nsIObserverService> observerService = mozilla::services::GetObserverService();
+  MOZ_ASSERT(observerService);
+  observerService->NotifyObservers(nullptr, "apz-repaints-flushed", nullptr);
+}
+
+static int32_t sActiveSuppressDisplayport = 0;
+static bool sDisplayPortSuppressionRespected = true;
+
+void
+APZCCallbackHelper::SuppressDisplayport(const bool& aEnabled,
+                                        const nsCOMPtr<nsIPresShell>& aShell)
+{
+  if (aEnabled) {
+    sActiveSuppressDisplayport++;
+  } else {
+    bool isSuppressed = IsDisplayportSuppressed();
+    sActiveSuppressDisplayport--;
+    if (isSuppressed && !IsDisplayportSuppressed() &&
+        aShell && aShell->GetRootFrame()) {
+      // We unsuppressed the displayport, trigger a paint
+      aShell->GetRootFrame()->SchedulePaint();
+    }
+  }
+
+  MOZ_ASSERT(sActiveSuppressDisplayport >= 0);
+}
+
+void
+APZCCallbackHelper::RespectDisplayPortSuppression(bool aEnabled,
+                                                  const nsCOMPtr<nsIPresShell>& aShell)
+{
+  bool isSuppressed = IsDisplayportSuppressed();
+  sDisplayPortSuppressionRespected = aEnabled;
+  if (isSuppressed && !IsDisplayportSuppressed() &&
+      aShell && aShell->GetRootFrame()) {
+    // We unsuppressed the displayport, trigger a paint
+    aShell->GetRootFrame()->SchedulePaint();
+  }
+}
+
+bool
+APZCCallbackHelper::IsDisplayportSuppressed()
+{
+  return sDisplayPortSuppressionRespected
+      && sActiveSuppressDisplayport > 0;
+}
+
+/* static */ bool
+APZCCallbackHelper::IsScrollInProgress(nsIScrollableFrame* aFrame)
+{
+  return aFrame->IsProcessingAsyncScroll()
+         || nsLayoutUtils::CanScrollOriginClobberApz(aFrame->LastScrollOrigin())
+         || aFrame->LastSmoothScrollOrigin();
+}
+
+/* static */ void
+APZCCallbackHelper::NotifyPinchGesture(PinchGestureInput::PinchGestureType aType,
+                                       LayoutDeviceCoord aSpanChange,
+                                       Modifiers aModifiers,
+                                       nsIWidget* aWidget)
+{
+  EventMessage msg;
+  switch (aType) {
+    case PinchGestureInput::PINCHGESTURE_START:
+      msg = eMagnifyGestureStart;
+      break;
+    case PinchGestureInput::PINCHGESTURE_SCALE:
+      msg = eMagnifyGestureUpdate;
+      break;
+    case PinchGestureInput::PINCHGESTURE_END:
+      msg = eMagnifyGesture;
+      break;
+    case PinchGestureInput::PINCHGESTURE_SENTINEL:
+    default:
+      MOZ_ASSERT_UNREACHABLE("Invalid gesture type");
+      return;
+  }
+
+  WidgetSimpleGestureEvent event(true, msg, aWidget);
+  event.mDelta = aSpanChange;
+  event.mModifiers = aModifiers;
+  DispatchWidgetEvent(event);
+}
+
+} // namespace layers
+} // namespace mozilla
+