Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

28 files changed, 4681 insertions, 0 deletions

diff --git a/gfx/layers/apz/util/APZCCallbackHelper.cpp b/gfx/layers/apz/util/APZCCallbackHelper.cpp
new file mode 100644
index 0000000000..8b67baf316
--- /dev/null
+++ b/gfx/layers/apz/util/APZCCallbackHelper.cpp
@@ -0,0 +1,940 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "gfxPlatform.h"  // For gfxPlatform::UseTiling
+
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/EventForwards.h"
+#include "mozilla/dom/CustomEvent.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/MouseEventBinding.h"
+#include "mozilla/dom/BrowserParent.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/IntegerPrintfMacros.h"
+#include "mozilla/layers/RepaintRequest.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/layers/WebRenderBridgeChild.h"
+#include "mozilla/DisplayPortUtils.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/ToString.h"
+#include "mozilla/ViewportUtils.h"
+#include "nsContainerFrame.h"
+#include "nsContentUtils.h"
+#include "nsIContent.h"
+#include "nsIDOMWindowUtils.h"
+#include "mozilla/dom/Document.h"
+#include "nsIInterfaceRequestorUtils.h"
+#include "nsIScrollableFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsPrintfCString.h"
+#include "nsPIDOMWindow.h"
+#include "nsRefreshDriver.h"
+#include "nsString.h"
+#include "nsView.h"
+
+static mozilla::LazyLogModule sApzHlpLog("apz.helper");
+#define APZCCH_LOG(...) MOZ_LOG(sApzHlpLog, LogLevel::Debug, (__VA_ARGS__))
+static mozilla::LazyLogModule sDisplayportLog("apz.displayport");
+
+namespace mozilla {
+namespace layers {
+
+using dom::BrowserParent;
+
+uint64_t APZCCallbackHelper::sLastTargetAPZCNotificationInputBlock =
+    uint64_t(-1);
+
+static ScreenMargin RecenterDisplayPort(const ScreenMargin& aDisplayPort) {
+  ScreenMargin margins = aDisplayPort;
+  margins.right = margins.left = margins.LeftRight() / 2;
+  margins.top = margins.bottom = margins.TopBottom() / 2;
+  return margins;
+}
+
+static PresShell* GetPresShell(const nsIContent* aContent) {
+  if (dom::Document* doc = aContent->GetComposedDoc()) {
+    return doc->GetPresShell();
+  }
+  return nullptr;
+}
+
+static CSSPoint ScrollFrameTo(nsIScrollableFrame* aFrame,
+                              const RepaintRequest& aRequest,
+                              bool& aSuccessOut) {
+  aSuccessOut = false;
+  CSSPoint targetScrollPosition = aRequest.GetLayoutScrollOffset();
+
+  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 (!aRequest.GetScrollOffsetUpdated()) {
+    return geckoScrollPosition;
+  }
+
+  // If this frame is overflow:hidden, then the expectation is that it was
+  // sized in a way that respects its scrollable boundaries. For the root
+  // frame, this means that it cannot be scrolled in such a way that it moves
+  // the layout viewport. For a non-root frame, this means that it cannot be
+  // scrolled at all.
+  //
+  // In either case, |targetScrollPosition| should be the same as
+  // |geckoScrollPosition| here.
+  //
+  // However, this is slightly racy. We query the overflow property of the
+  // scroll frame at the time the repaint request arrives at the main thread
+  // (i.e., right now), but APZ made the decision of whether or not to allow
+  // scrolling based on the information it had at the time it processed the
+  // scroll event. The overflow property could have changed at some time
+  // between the two events and so APZ may have computed a scrollable region
+  // that is larger than what is actually allowed.
+  //
+  // Currently, we allow the scroll position to change even though the frame is
+  // overflow:hidden (that is, we take |targetScrollPosition|). If this turns
+  // out to be problematic, an alternative solution would be to ignore the
+  // scroll position change (that is, use |geckoScrollPosition|).
+  if (aFrame->GetScrollStyles().mVertical == StyleOverflow::Hidden &&
+      targetScrollPosition.y != geckoScrollPosition.y) {
+    NS_WARNING(
+        nsPrintfCString(
+            "APZCCH: targetScrollPosition.y (%f) != geckoScrollPosition.y (%f)",
+            targetScrollPosition.y.value, geckoScrollPosition.y.value)
+            .get());
+  }
+  if (aFrame->GetScrollStyles().mHorizontal == StyleOverflow::Hidden &&
+      targetScrollPosition.x != geckoScrollPosition.x) {
+    NS_WARNING(
+        nsPrintfCString(
+            "APZCCH: targetScrollPosition.x (%f) != geckoScrollPosition.x (%f)",
+            targetScrollPosition.x.value, geckoScrollPosition.x.value)
+            .get());
+  }
+
+  // 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) {
+    ScrollSnapTargetIds snapTargetIds = aRequest.GetLastSnapTargetIds();
+    aFrame->ScrollToCSSPixelsForApz(targetScrollPosition,
+                                    std::move(snapTargetIds));
+    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 |aRequest|.
+ *
+ * Any difference between the requested and actual scroll positions is used to
+ * update the callback-transform stored on the content, and return a new
+ * display port.
+ */
+static DisplayPortMargins ScrollFrame(nsIContent* aContent,
+                                      const RepaintRequest& aRequest) {
+  // Scroll the window to the desired spot
+  nsIScrollableFrame* sf =
+      nsLayoutUtils::FindScrollableFrameFor(aRequest.GetScrollId());
+  if (sf) {
+    sf->ResetScrollInfoIfNeeded(aRequest.GetScrollGeneration(),
+                                aRequest.GetScrollGenerationOnApz(),
+                                aRequest.GetScrollAnimationType(),
+                                nsIScrollableFrame::InScrollingGesture(
+                                    aRequest.IsInScrollingGesture()));
+    sf->SetScrollableByAPZ(!aRequest.IsScrollInfoLayer());
+    if (sf->IsRootScrollFrameOfDocument()) {
+      if (!APZCCallbackHelper::IsScrollInProgress(sf)) {
+        APZCCH_LOG("Setting VV offset to %s\n",
+                   ToString(aRequest.GetVisualScrollOffset()).c_str());
+        if (sf->SetVisualViewportOffset(
+                CSSPoint::ToAppUnits(aRequest.GetVisualScrollOffset()),
+                /* aRepaint = */ false)) {
+          // sf can't be destroyed if SetVisualViewportOffset returned true.
+          sf->MarkEverScrolled();
+        }
+      }
+    }
+  }
+  // sf might have been destroyed by the call to SetVisualViewportOffset, so
+  // re-get it.
+  sf = nsLayoutUtils::FindScrollableFrameFor(aRequest.GetScrollId());
+  bool scrollUpdated = false;
+  auto displayPortMargins =
+      DisplayPortMargins::ForScrollFrame(sf, aRequest.GetDisplayPortMargins());
+  CSSPoint apzScrollOffset = aRequest.GetVisualScrollOffset();
+  CSSPoint actualScrollOffset = ScrollFrameTo(sf, aRequest, scrollUpdated);
+  CSSPoint scrollDelta = apzScrollOffset - actualScrollOffset;
+
+  if (scrollUpdated) {
+    if (aRequest.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 the requested
+      // and actual scroll offsets.
+      displayPortMargins =
+          DisplayPortMargins::FromAPZ(aRequest.GetDisplayPortMargins(),
+                                      apzScrollOffset, actualScrollOffset);
+    }
+  } else if (aRequest.IsRootContent() &&
+             apzScrollOffset != aRequest.GetLayoutScrollOffset()) {
+    // APZ uses the visual viewport's offset to calculate where to place the
+    // display port, so the display port is misplaced when a pinch zoom occurs.
+    //
+    // We need to force a display port adjustment in the following paint to
+    // account for a difference between the requested and actual scroll
+    // offsets in repaints requested by
+    // AsyncPanZoomController::NotifyLayersUpdated.
+    displayPortMargins = DisplayPortMargins::FromAPZ(
+        aRequest.GetDisplayPortMargins(), apzScrollOffset, 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.
+    displayPortMargins = DisplayPortMargins::ForScrollFrame(
+        sf, RecenterDisplayPort(aRequest.GetDisplayPortMargins()));
+  }
+
+  // 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() != aRequest.GetScrollGeneration() &&
+      nsLayoutUtils::CanScrollOriginClobberApz(sf->LastScrollOrigin());
+  if (aContent && !mainThreadScrollChanged) {
+    aContent->SetProperty(nsGkAtoms::apzCallbackTransform,
+                          new CSSPoint(scrollDelta),
+                          nsINode::DeleteProperty<CSSPoint>);
+  }
+
+  return displayPortMargins;
+}
+
+static void SetDisplayPortMargins(PresShell* aPresShell, nsIContent* aContent,
+                                  const DisplayPortMargins& aDisplayPortMargins,
+                                  CSSSize aDisplayPortBase) {
+  if (!aContent) {
+    return;
+  }
+
+  bool hadDisplayPort = DisplayPortUtils::HasDisplayPort(aContent);
+  if (MOZ_LOG_TEST(sDisplayportLog, LogLevel::Debug)) {
+    if (!hadDisplayPort) {
+      mozilla::layers::ScrollableLayerGuid::ViewID viewID =
+          mozilla::layers::ScrollableLayerGuid::NULL_SCROLL_ID;
+      nsLayoutUtils::FindIDFor(aContent, &viewID);
+      MOZ_LOG(
+          sDisplayportLog, LogLevel::Debug,
+          ("APZCCH installing displayport margins %s on scrollId=%" PRIu64 "\n",
+           ToString(aDisplayPortMargins).c_str(), viewID));
+    }
+  }
+  DisplayPortUtils::SetDisplayPortMargins(
+      aContent, aPresShell, aDisplayPortMargins,
+      hadDisplayPort ? DisplayPortUtils::ClearMinimalDisplayPortProperty::No
+                     : DisplayPortUtils::ClearMinimalDisplayPortProperty::Yes,
+      0);
+  if (!hadDisplayPort) {
+    DisplayPortUtils::SetZeroMarginDisplayPortOnAsyncScrollableAncestors(
+        aContent->GetPrimaryFrame());
+  }
+
+  nsRect base(0, 0, aDisplayPortBase.width * AppUnitsPerCSSPixel(),
+              aDisplayPortBase.height * AppUnitsPerCSSPixel());
+  DisplayPortUtils::SetDisplayPortBaseIfNotSet(aContent, base);
+}
+
+static void SetPaintRequestTime(nsIContent* aContent,
+                                const TimeStamp& aPaintRequestTime) {
+  aContent->SetProperty(nsGkAtoms::paintRequestTime,
+                        new TimeStamp(aPaintRequestTime),
+                        nsINode::DeleteProperty<TimeStamp>);
+}
+
+void APZCCallbackHelper::NotifyLayerTransforms(
+    const nsTArray<MatrixMessage>& aTransforms) {
+  MOZ_ASSERT(NS_IsMainThread());
+  for (const MatrixMessage& msg : aTransforms) {
+    BrowserParent* parent =
+        BrowserParent::GetBrowserParentFromLayersId(msg.GetLayersId());
+    if (parent) {
+      parent->SetChildToParentConversionMatrix(
+          ViewAs<LayoutDeviceToLayoutDeviceMatrix4x4>(
+              msg.GetMatrix(),
+              PixelCastJustification::ContentProcessIsLayerInUiProcess),
+          msg.GetTopLevelViewportVisibleRectInBrowserCoords());
+    }
+  }
+}
+
+void APZCCallbackHelper::UpdateRootFrame(const RepaintRequest& aRequest) {
+  if (aRequest.GetScrollId() == ScrollableLayerGuid::NULL_SCROLL_ID) {
+    return;
+  }
+  RefPtr<nsIContent> content =
+      nsLayoutUtils::FindContentFor(aRequest.GetScrollId());
+  if (!content) {
+    return;
+  }
+
+  RefPtr<PresShell> presShell = GetPresShell(content);
+  if (!presShell || aRequest.GetPresShellId() != presShell->GetPresShellId()) {
+    return;
+  }
+
+  APZCCH_LOG("Handling request %s\n", ToString(aRequest).c_str());
+  if (nsLayoutUtils::AllowZoomingForDocument(presShell->GetDocument()) &&
+      aRequest.GetAsyncZoom().scale != 1.0) {
+    // 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 visual viewport size is bad because it can cause a
+    // stale value to be returned by window.innerWidth/innerHeight (see bug
+    // 1187792).
+
+    float presShellResolution = presShell->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.
+    // One might think that if the last ResolutionChangeOrigin was apz then the
+    // pres shell resolutions should match but
+    // that is not the case. We can get multiple repaint requests that has the
+    // same pres shell resolution (because apz didn't receive a content layers
+    // update inbetween) if the first has async zoom we apply that and chance
+    // the content pres shell resolution and thus when handling the second
+    // repaint request the pres shell resolution won't match. So that's why we
+    // also check if the last resolution change origin was apz (aka 'us').
+    if (!FuzzyEqualsMultiplicative(presShellResolution,
+                                   aRequest.GetPresShellResolution()) &&
+        presShell->GetLastResolutionChangeOrigin() !=
+            ResolutionChangeOrigin::Apz) {
+      return;
+    }
+
+    // The pres shell resolution is updated by the the async zoom since the
+    // last paint.
+    // We want to calculate the new presshell resolution as
+    // |aRequest.GetPresShellResolution() * aRequest.GetAsyncZoom()| but that
+    // calculation can lead to small inaccuracies due to limited floating point
+    // precision. Specifically,
+    // clang-format off
+    // asyncZoom = zoom / layerPixelsPerCSSPixel
+    //           = zoom / (devPixelsPerCSSPixel * cumulativeResolution)
+    // clang-format on
+    // Since this is a root frame we generally do not allow css transforms to
+    // scale it, so it is very likely that cumulativeResolution ==
+    // presShellResoluion. So
+    // clang-format off
+    // newPresShellResoluion = presShellResoluion * asyncZoom
+    // = presShellResoluion * zoom / (devPixelsPerCSSPixel * presShellResoluion)
+    // = zoom / devPixelsPerCSSPixel
+    // clang-format on
+    // However, we want to keep the calculation general and so we do not assume
+    // presShellResoluion == cumulativeResolution, but rather factor those
+    // values out so they cancel and the floating point division has a very high
+    // probability of being exactly 1.
+    presShellResolution =
+        (aRequest.GetPresShellResolution() /
+         aRequest.GetCumulativeResolution().scale) *
+        (aRequest.GetZoom() / aRequest.GetDevPixelsPerCSSPixel()).scale;
+    presShell->SetResolutionAndScaleTo(presShellResolution,
+                                       ResolutionChangeOrigin::Apz);
+
+    // Changing the resolution will trigger a reflow which will cause the
+    // main-thread scroll position to be realigned in layer pixels. This
+    // (subpixel) scroll mutation can trigger a scroll update to APZ which
+    // is undesirable. Instead of having that happen as part of the post-reflow
+    // code, we force it to happen here with ScrollOrigin::Apz so that it
+    // doesn't trigger a scroll update to APZ.
+    nsIScrollableFrame* sf =
+        nsLayoutUtils::FindScrollableFrameFor(aRequest.GetScrollId());
+    CSSPoint currentScrollPosition =
+        CSSPoint::FromAppUnits(sf->GetScrollPosition());
+    ScrollSnapTargetIds snapTargetIds = aRequest.GetLastSnapTargetIds();
+    sf->ScrollToCSSPixelsForApz(currentScrollPosition,
+                                std::move(snapTargetIds));
+  }
+
+  // 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.
+  DisplayPortMargins displayPortMargins = ScrollFrame(content, aRequest);
+
+  SetDisplayPortMargins(presShell, content, displayPortMargins,
+                        aRequest.CalculateCompositedSizeInCssPixels());
+  SetPaintRequestTime(content, aRequest.GetPaintRequestTime());
+}
+
+void APZCCallbackHelper::UpdateSubFrame(const RepaintRequest& aRequest) {
+  if (aRequest.GetScrollId() == ScrollableLayerGuid::NULL_SCROLL_ID) {
+    return;
+  }
+  RefPtr<nsIContent> content =
+      nsLayoutUtils::FindContentFor(aRequest.GetScrollId());
+  if (!content) {
+    return;
+  }
+
+  // We don't currently support zooming for subframes, so nothing extra
+  // needs to be done beyond the tasks common to this and UpdateRootFrame.
+  DisplayPortMargins displayPortMargins = ScrollFrame(content, aRequest);
+  if (RefPtr<PresShell> presShell = GetPresShell(content)) {
+    SetDisplayPortMargins(presShell, content, displayPortMargins,
+                          aRequest.CalculateCompositedSizeInCssPixels());
+  }
+  SetPaintRequestTime(content, aRequest.GetPaintRequestTime());
+}
+
+bool APZCCallbackHelper::GetOrCreateScrollIdentifiers(
+    nsIContent* aContent, uint32_t* aPresShellIdOut,
+    ScrollableLayerGuid::ViewID* aViewIdOut) {
+  if (!aContent) {
+    return false;
+  }
+  *aViewIdOut = nsLayoutUtils::FindOrCreateIDFor(aContent);
+  if (PresShell* presShell = GetPresShell(aContent)) {
+    *aPresShellIdOut = presShell->GetPresShellId();
+    return true;
+  }
+  return false;
+}
+
+void APZCCallbackHelper::InitializeRootDisplayport(PresShell* 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;
+  ScrollableLayerGuid::ViewID viewId;
+  if (APZCCallbackHelper::GetOrCreateScrollIdentifiers(content, &presShellId,
+                                                       &viewId)) {
+    MOZ_LOG(
+        sDisplayportLog, LogLevel::Debug,
+        ("Initializing root displayport on scrollId=%" PRIu64 "\n", viewId));
+    Maybe<nsRect> baseRect =
+        DisplayPortUtils::GetRootDisplayportBase(aPresShell);
+    if (baseRect) {
+      DisplayPortUtils::SetDisplayPortBaseIfNotSet(content, *baseRect);
+    }
+
+    DisplayPortUtils::SetDisplayPortMargins(
+        content, aPresShell, DisplayPortMargins::Empty(content),
+        DisplayPortUtils::ClearMinimalDisplayPortProperty::Yes, 0);
+    DisplayPortUtils::SetZeroMarginDisplayPortOnAsyncScrollableAncestors(
+        content->GetPrimaryFrame());
+  }
+}
+
+nsPresContext* APZCCallbackHelper::GetPresContextForContent(
+    nsIContent* aContent) {
+  dom::Document* doc = aContent->GetComposedDoc();
+  if (!doc) {
+    return nullptr;
+  }
+  PresShell* presShell = doc->GetPresShell();
+  if (!presShell) {
+    return nullptr;
+  }
+  return presShell->GetPresContext();
+}
+
+PresShell* APZCCallbackHelper::GetRootContentDocumentPresShellForContent(
+    nsIContent* aContent) {
+  nsPresContext* context = GetPresContextForContent(aContent);
+  if (!context) {
+    return nullptr;
+  }
+  context = context->GetInProcessRootContentDocumentPresContext();
+  if (!context) {
+    return nullptr;
+  }
+  return context->PresShell();
+}
+
+nsEventStatus APZCCallbackHelper::DispatchWidgetEvent(WidgetGUIEvent& aEvent) {
+  nsEventStatus status = nsEventStatus_eConsumeNoDefault;
+  if (aEvent.mWidget) {
+    aEvent.mWidget->DispatchEvent(&aEvent, status);
+  }
+  return status;
+}
+
+nsEventStatus APZCCallbackHelper::DispatchSynthesizedMouseEvent(
+    EventMessage aMsg, 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.mButton = MouseButton::ePrimary;
+  event.mButtons |= MouseButtonsFlag::ePrimaryFlag;
+  event.mInputSource = dom::MouseEvent_Binding::MOZ_SOURCE_TOUCH;
+  if (aMsg == eMouseLongTap) {
+    event.mFlags.mOnlyChromeDispatch = 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);
+}
+
+PreventDefaultResult APZCCallbackHelper::DispatchMouseEvent(
+    PresShell* aPresShell, const nsString& aType, const CSSPoint& aPoint,
+    int32_t aButton, int32_t aClickCount, int32_t aModifiers,
+    unsigned short aInputSourceArg, uint32_t aPointerId) {
+  NS_ENSURE_TRUE(aPresShell, PreventDefaultResult::ByContent);
+
+  PreventDefaultResult preventDefaultResult;
+  nsContentUtils::SendMouseEvent(
+      aPresShell, aType, aPoint.x, aPoint.y, aButton,
+      nsIDOMWindowUtils::MOUSE_BUTTONS_NOT_SPECIFIED, aClickCount, aModifiers,
+      /* aIgnoreRootScrollFrame = */ false, 0, aInputSourceArg, aPointerId,
+      false, &preventDefaultResult, false,
+      /* aIsWidgetEventSynthesized = */ false);
+  return preventDefaultResult;
+}
+
+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",
+             ToString(aPoint).c_str());
+  DispatchSynthesizedMouseEvent(eMouseMove, aPoint, aModifiers, aClickCount,
+                                aWidget);
+  DispatchSynthesizedMouseEvent(eMouseDown, aPoint, aModifiers, aClickCount,
+                                aWidget);
+  DispatchSynthesizedMouseEvent(eMouseUp, 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 (PresShell* presShell = view->GetPresShell()) {
+      MOZ_ASSERT(presShell->GetDocument());
+      return presShell->GetDocument()->GetDocumentElement();
+    }
+  }
+  return nullptr;
+}
+
+namespace {
+
+using FrameForPointOption = nsLayoutUtils::FrameForPointOption;
+
+// 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 the frame had a displayport that has already been
+// painted (in this case, the caller can send the SetTargetAPZC notification
+// right away, rather than waiting for a transaction to propagate the
+// displayport to APZ first).
+static bool PrepareForSetTargetAPZCNotification(
+    nsIWidget* aWidget, const LayersId& aLayersId, nsIFrame* aRootFrame,
+    const LayoutDeviceIntPoint& aRefPoint,
+    nsTArray<ScrollableLayerGuid>* aTargets) {
+  ScrollableLayerGuid guid(aLayersId, 0, ScrollableLayerGuid::NULL_SCROLL_ID);
+  RelativeTo relativeTo{aRootFrame, ViewportType::Visual};
+  nsPoint point = nsLayoutUtils::GetEventCoordinatesRelativeTo(
+      aWidget, aRefPoint, relativeTo);
+  nsIFrame* target = nsLayoutUtils::GetFrameForPoint(relativeTo, point);
+  nsIScrollableFrame* scrollAncestor =
+      target ? nsLayoutUtils::GetAsyncScrollableAncestorFrame(target)
+             : aRootFrame->PresShell()->GetRootScrollFrameAsScrollable();
+
+  // Assuming that if there's no scrollAncestor, there's already a displayPort.
+  nsCOMPtr<dom::Element> dpElement =
+      scrollAncestor ? GetDisplayportElementFor(scrollAncestor)
+                     : GetRootDocumentElementFor(aWidget);
+
+  if (MOZ_LOG_TEST(sApzHlpLog, LogLevel::Debug)) {
+    nsAutoString dpElementDesc;
+    if (dpElement) {
+      dpElement->Describe(dpElementDesc);
+    }
+    APZCCH_LOG("For event at %s found scrollable element %p (%s)\n",
+               ToString(aRefPoint).c_str(), dpElement.get(),
+               NS_LossyConvertUTF16toASCII(dpElementDesc).get());
+  }
+
+  bool guidIsValid = APZCCallbackHelper::GetOrCreateScrollIdentifiers(
+      dpElement, &(guid.mPresShellId), &(guid.mScrollId));
+  aTargets->AppendElement(guid);
+
+  if (!guidIsValid) {
+    return false;
+  }
+  if (DisplayPortUtils::HasNonMinimalNonZeroDisplayPort(dpElement)) {
+    // If the element has a displayport but it hasn't been painted yet,
+    // we want the caller to wait for the paint to happen, but we don't
+    // need to set the displayport here since it's already been set.
+    return !DisplayPortUtils::HasPaintedDisplayPort(dpElement);
+  }
+
+  if (!scrollAncestor) {
+    // This can happen if the document element gets swapped out after
+    // ChromeProcessController runs InitializeRootDisplayport. In this case
+    // let's try to set a displayport 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->PresShell());
+    return false;
+  }
+
+  APZCCH_LOG("%p didn't have a displayport, so setting one...\n",
+             dpElement.get());
+  MOZ_LOG(sDisplayportLog, LogLevel::Debug,
+          ("Activating displayport on scrollId=%" PRIu64 " for SetTargetAPZC\n",
+           guid.mScrollId));
+  bool activated = DisplayPortUtils::CalculateAndSetDisplayPortMargins(
+      scrollAncestor, DisplayPortUtils::RepaintMode::Repaint);
+  if (!activated) {
+    return false;
+  }
+
+  nsIFrame* frame = do_QueryFrame(scrollAncestor);
+  DisplayPortUtils::SetZeroMarginDisplayPortOnAsyncScrollableAncestors(frame);
+
+  return !DisplayPortUtils::HasPaintedDisplayPort(dpElement);
+}
+
+static void SendLayersDependentApzcTargetConfirmation(
+    nsIWidget* aWidget, uint64_t aInputBlockId,
+    nsTArray<ScrollableLayerGuid>&& aTargets) {
+  WindowRenderer* renderer = aWidget->GetWindowRenderer();
+  if (!renderer) {
+    return;
+  }
+
+  if (WebRenderLayerManager* wrlm = renderer->AsWebRender()) {
+    if (WebRenderBridgeChild* wrbc = wrlm->WrBridge()) {
+      wrbc->SendSetConfirmedTargetAPZC(aInputBlockId, aTargets);
+    }
+    return;
+  }
+}
+
+}  // namespace
+
+DisplayportSetListener::DisplayportSetListener(
+    nsIWidget* aWidget, nsPresContext* aPresContext,
+    const uint64_t& aInputBlockId, nsTArray<ScrollableLayerGuid>&& aTargets)
+    : ManagedPostRefreshObserver(aPresContext),
+      mWidget(aWidget),
+      mInputBlockId(aInputBlockId),
+      mTargets(std::move(aTargets)) {
+  MOZ_ASSERT(!mAction, "Setting Action twice");
+  mAction = [instance = MOZ_KnownLive(this)](bool aWasCanceled) {
+    instance->OnPostRefresh();
+    return Unregister::Yes;
+  };
+}
+
+DisplayportSetListener::~DisplayportSetListener() = default;
+
+void DisplayportSetListener::Register() {
+  APZCCH_LOG("DisplayportSetListener::Register\n");
+  mPresContext->RegisterManagedPostRefreshObserver(this);
+}
+
+void DisplayportSetListener::OnPostRefresh() {
+  APZCCH_LOG("Got refresh, sending target APZCs for input block %" PRIu64 "\n",
+             mInputBlockId);
+  SendLayersDependentApzcTargetConfirmation(mWidget, mInputBlockId,
+                                            std::move(mTargets));
+}
+
+already_AddRefed<DisplayportSetListener>
+APZCCallbackHelper::SendSetTargetAPZCNotification(nsIWidget* aWidget,
+                                                  dom::Document* aDocument,
+                                                  const WidgetGUIEvent& aEvent,
+                                                  const LayersId& aLayersId,
+                                                  uint64_t aInputBlockId) {
+  if (!aWidget || !aDocument) {
+    return nullptr;
+  }
+  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 nullptr;
+  }
+  sLastTargetAPZCNotificationInputBlock = aInputBlockId;
+  if (PresShell* presShell = aDocument->GetPresShell()) {
+    if (nsIFrame* rootFrame = presShell->GetRootFrame()) {
+      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, aLayersId, rootFrame, touchEvent->mTouches[i]->mRefPoint,
+              &targets);
+        }
+      } else if (const WidgetWheelEvent* wheelEvent = aEvent.AsWheelEvent()) {
+        waitForRefresh = PrepareForSetTargetAPZCNotification(
+            aWidget, aLayersId, rootFrame, wheelEvent->mRefPoint, &targets);
+      } else if (const WidgetMouseEvent* mouseEvent = aEvent.AsMouseEvent()) {
+        waitForRefresh = PrepareForSetTargetAPZCNotification(
+            aWidget, aLayersId, rootFrame, mouseEvent->mRefPoint, &targets);
+      }
+      // TODO: Do other types of events need to be handled?
+
+      if (!targets.IsEmpty()) {
+        if (waitForRefresh) {
+          APZCCH_LOG(
+              "At least one target got a new displayport, need to wait for "
+              "refresh\n");
+          return MakeAndAddRef<DisplayportSetListener>(
+              aWidget, presShell->GetPresContext(), aInputBlockId,
+              std::move(targets));
+        }
+        APZCCH_LOG("Sending target APZCs for input block %" PRIu64 "\n",
+                   aInputBlockId);
+        aWidget->SetConfirmedTargetAPZC(aInputBlockId, targets);
+      }
+    }
+  }
+  return nullptr;
+}
+
+void APZCCallbackHelper::NotifyMozMouseScrollEvent(
+    const ScrollableLayerGuid::ViewID& aScrollId, const nsString& aEvent) {
+  nsCOMPtr<nsIContent> targetContent = nsLayoutUtils::FindContentFor(aScrollId);
+  if (!targetContent) {
+    return;
+  }
+  RefPtr<dom::Document> ownerDoc = targetContent->OwnerDoc();
+  if (!ownerDoc) {
+    return;
+  }
+
+  nsContentUtils::DispatchEventOnlyToChrome(ownerDoc, targetContent, aEvent,
+                                            CanBubble::eYes, Cancelable::eYes);
+}
+
+void APZCCallbackHelper::NotifyFlushComplete(PresShell* aPresShell) {
+  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 (aPresShell && aPresShell->GetRootFrame()) {
+    aPresShell->GetRootFrame()->SchedulePaint(nsIFrame::PAINT_DEFAULT, false);
+  }
+
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  MOZ_ASSERT(observerService);
+  observerService->NotifyObservers(nullptr, "apz-repaints-flushed", nullptr);
+}
+
+/* static */
+bool APZCCallbackHelper::IsScrollInProgress(nsIScrollableFrame* aFrame) {
+  using AnimationState = nsIScrollableFrame::AnimationState;
+
+  return aFrame->ScrollAnimationState().contains(AnimationState::MainThread) ||
+         nsLayoutUtils::CanScrollOriginClobberApz(aFrame->LastScrollOrigin());
+}
+
+/* static */
+void APZCCallbackHelper::NotifyAsyncScrollbarDragInitiated(
+    uint64_t aDragBlockId, const ScrollableLayerGuid::ViewID& aScrollId,
+    ScrollDirection aDirection) {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (nsIScrollableFrame* scrollFrame =
+          nsLayoutUtils::FindScrollableFrameFor(aScrollId)) {
+    scrollFrame->AsyncScrollbarDragInitiated(aDragBlockId, aDirection);
+  }
+}
+
+/* static */
+void APZCCallbackHelper::NotifyAsyncScrollbarDragRejected(
+    const ScrollableLayerGuid::ViewID& aScrollId) {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (nsIScrollableFrame* scrollFrame =
+          nsLayoutUtils::FindScrollableFrameFor(aScrollId)) {
+    scrollFrame->AsyncScrollbarDragRejected();
+  }
+}
+
+/* static */
+void APZCCallbackHelper::NotifyAsyncAutoscrollRejected(
+    const ScrollableLayerGuid::ViewID& aScrollId) {
+  MOZ_ASSERT(NS_IsMainThread());
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  MOZ_ASSERT(observerService);
+
+  nsAutoString data;
+  data.AppendInt(aScrollId);
+  observerService->NotifyObservers(nullptr, "autoscroll-rejected-by-apz",
+                                   data.get());
+}
+
+/* static */
+void APZCCallbackHelper::CancelAutoscroll(
+    const ScrollableLayerGuid::ViewID& aScrollId) {
+  MOZ_ASSERT(NS_IsMainThread());
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  MOZ_ASSERT(observerService);
+
+  nsAutoString data;
+  data.AppendInt(aScrollId);
+  observerService->NotifyObservers(nullptr, "apz:cancel-autoscroll",
+                                   data.get());
+}
+
+/* static */
+void APZCCallbackHelper::NotifyScaleGestureComplete(
+    const nsCOMPtr<nsIWidget>& aWidget, float aScale) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (nsView* view = nsView::GetViewFor(aWidget)) {
+    if (PresShell* presShell = view->GetPresShell()) {
+      dom::Document* doc = presShell->GetDocument();
+      MOZ_ASSERT(doc);
+      if (nsPIDOMWindowInner* win = doc->GetInnerWindow()) {
+        dom::AutoJSAPI jsapi;
+        if (!jsapi.Init(win)) {
+          return;
+        }
+
+        JSContext* cx = jsapi.cx();
+        JS::Rooted<JS::Value> detail(cx, JS::Float32Value(aScale));
+        RefPtr<dom::CustomEvent> event =
+            NS_NewDOMCustomEvent(doc, nullptr, nullptr);
+        event->InitCustomEvent(cx, u"MozScaleGestureComplete"_ns,
+                               /* CanBubble */ true,
+                               /* Cancelable */ false, detail);
+        event->SetTrusted(true);
+        AsyncEventDispatcher* dispatcher = new AsyncEventDispatcher(doc, event);
+        dispatcher->mOnlyChromeDispatch = ChromeOnlyDispatch::eYes;
+
+        dispatcher->PostDOMEvent();
+      }
+    }
+  }
+}
+
+/* static */
+void APZCCallbackHelper::NotifyPinchGesture(
+    PinchGestureInput::PinchGestureType aType,
+    const LayoutDevicePoint& aFocusPoint, LayoutDeviceCoord aSpanChange,
+    Modifiers aModifiers, const nsCOMPtr<nsIWidget>& aWidget) {
+  APZCCH_LOG("APZCCallbackHelper dispatching pinch gesture\n");
+  EventMessage msg;
+  switch (aType) {
+    case PinchGestureInput::PINCHGESTURE_START:
+      msg = eMagnifyGestureStart;
+      break;
+    case PinchGestureInput::PINCHGESTURE_SCALE:
+      msg = eMagnifyGestureUpdate;
+      break;
+    case PinchGestureInput::PINCHGESTURE_FINGERLIFTED:
+    case PinchGestureInput::PINCHGESTURE_END:
+      msg = eMagnifyGesture;
+      break;
+  }
+
+  WidgetSimpleGestureEvent event(true, msg, aWidget.get());
+  // XXX mDelta for the eMagnifyGesture event is supposed to be the
+  // cumulative magnification over the entire gesture (per docs in
+  // SimpleGestureEvent.webidl) but currently APZ just sends us a zero
+  // aSpanChange for that event, so the mDelta is wrong. Nothing relies
+  // on that currently, but we might want to fix it at some point.
+  event.mDelta = aSpanChange;
+  event.mModifiers = aModifiers;
+  event.mRefPoint = RoundedToInt(aFocusPoint);
+
+  DispatchWidgetEvent(event);
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/APZCCallbackHelper.h b/gfx/layers/apz/util/APZCCallbackHelper.h
new file mode 100644
index 0000000000..7b1f7cb88b
--- /dev/null
+++ b/gfx/layers/apz/util/APZCCallbackHelper.h
@@ -0,0 +1,195 @@
+/* -*- 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/. */
+
+#ifndef mozilla_layers_APZCCallbackHelper_h
+#define mozilla_layers_APZCCallbackHelper_h
+
+#include "InputData.h"
+#include "LayersTypes.h"
+#include "Units.h"
+#include "mozilla/EventForwards.h"
+#include "mozilla/layers/MatrixMessage.h"
+#include "nsRefreshObservers.h"
+
+#include <functional>
+
+class nsIContent;
+class nsIScrollableFrame;
+class nsIWidget;
+class nsPresContext;
+template <class T>
+struct already_AddRefed;
+template <class T>
+class nsCOMPtr;
+
+namespace mozilla {
+
+class PresShell;
+enum class PreventDefaultResult : uint8_t;
+
+namespace layers {
+
+struct RepaintRequest;
+
+/* Refer to documentation on SendSetTargetAPZCNotification for this class */
+class DisplayportSetListener : public ManagedPostRefreshObserver {
+ public:
+  DisplayportSetListener(nsIWidget* aWidget, nsPresContext*,
+                         const uint64_t& aInputBlockId,
+                         nsTArray<ScrollableLayerGuid>&& aTargets);
+  virtual ~DisplayportSetListener();
+  void Register();
+
+ private:
+  RefPtr<nsIWidget> mWidget;
+  uint64_t mInputBlockId;
+  nsTArray<ScrollableLayerGuid> mTargets;
+
+  void OnPostRefresh();
+};
+
+/* This class contains some helper methods that facilitate implementing the
+   GeckoContentController callback interface required by the
+   AsyncPanZoomController. Since different platforms need to implement this
+   interface in similar-but- not-quite-the-same ways, this utility class
+   provides some helpful methods to hold code that can be shared across the
+   different platform implementations.
+ */
+class APZCCallbackHelper {
+  typedef mozilla::layers::ScrollableLayerGuid ScrollableLayerGuid;
+
+ public:
+  static void NotifyLayerTransforms(const nsTArray<MatrixMessage>& aTransforms);
+
+  /* Applies the scroll and zoom parameters from the given RepaintRequest object
+     to the root frame for the given metrics' scrollId. If tiled thebes layers
+     are enabled, this will align the displayport to tile boundaries. Setting
+     the scroll position can cause some small adjustments to be made to the
+     actual scroll position. */
+  static void UpdateRootFrame(const RepaintRequest& aRequest);
+
+  /* Applies the scroll parameters from the given RepaintRequest object to the
+     subframe corresponding to given metrics' scrollId. If tiled thebes
+     layers are enabled, this will align the displayport to tile boundaries.
+     Setting the scroll position can cause some small adjustments to be made
+     to the actual scroll position. */
+  static void UpdateSubFrame(const RepaintRequest& aRequest);
+
+  /* Get the presShellId and view ID for the given content element.
+   * If the view ID does not exist, one is created.
+   * The pres shell ID should generally already exist; if it doesn't for some
+   * reason, false is returned. */
+  static bool GetOrCreateScrollIdentifiers(
+      nsIContent* aContent, uint32_t* aPresShellIdOut,
+      ScrollableLayerGuid::ViewID* aViewIdOut);
+
+  /* Initialize a zero-margin displayport on the root document element of the
+     given presShell. */
+  static void InitializeRootDisplayport(PresShell* aPresShell);
+
+  /* Get the pres context associated with the document enclosing |aContent|. */
+  static nsPresContext* GetPresContextForContent(nsIContent* aContent);
+
+  /* Get the pres shell associated with the root content document enclosing
+   * |aContent|. */
+  static PresShell* GetRootContentDocumentPresShellForContent(
+      nsIContent* aContent);
+
+  /* Dispatch a widget event via the widget stored in the event, if any.
+   * In a child process, allows the BrowserParent event-capture mechanism to
+   * intercept the event. */
+  static nsEventStatus DispatchWidgetEvent(WidgetGUIEvent& aEvent);
+
+  /* Synthesize a mouse event with the given parameters, and dispatch it
+   * via the given widget. */
+  static nsEventStatus DispatchSynthesizedMouseEvent(
+      EventMessage aMsg, const LayoutDevicePoint& aRefPoint,
+      Modifiers aModifiers, int32_t aClickCount, nsIWidget* aWidget);
+
+  /* Dispatch a mouse event with the given parameters.
+   * Return whether or not any listeners have called preventDefault on the
+   * event.
+   * This is a lightweight wrapper around nsContentUtils::SendMouseEvent()
+   * and as such expects |aPoint| to be in layout coordinates. */
+  MOZ_CAN_RUN_SCRIPT
+  static PreventDefaultResult DispatchMouseEvent(
+      PresShell* aPresShell, const nsString& aType, const CSSPoint& aPoint,
+      int32_t aButton, int32_t aClickCount, int32_t aModifiers,
+      unsigned short aInputSourceArg, uint32_t aPointerId);
+
+  /* Fire a single-tap event at the given point. The event is dispatched
+   * via the given widget. */
+  static void FireSingleTapEvent(const LayoutDevicePoint& aPoint,
+                                 Modifiers aModifiers, int32_t aClickCount,
+                                 nsIWidget* aWidget);
+
+  /* Perform hit-testing on the touch points of |aEvent| to determine
+   * which scrollable frames they target. If any of these frames don't have
+   * a displayport, set one.
+   *
+   * If any displayports need to be set, this function returns a heap-allocated
+   * object. The caller is responsible for calling Register() on that object.
+   *
+   * The object registers itself as a post-refresh observer on the presShell
+   * and ensures that notifications get sent to APZ correctly after the
+   * refresh.
+   *
+   * Having the caller manage this object is desirable in case they want to
+   * (a) know about the fact that a displayport needs to be set, and
+   * (b) register a post-refresh observer of their own that will run in
+   *     a defined ordering relative to the APZ messages.
+   */
+  static already_AddRefed<DisplayportSetListener> SendSetTargetAPZCNotification(
+      nsIWidget* aWidget, mozilla::dom::Document* aDocument,
+      const WidgetGUIEvent& aEvent, const LayersId& aLayersId,
+      uint64_t aInputBlockId);
+
+  /* Notify content of a mouse scroll testing event. */
+  static void NotifyMozMouseScrollEvent(
+      const ScrollableLayerGuid::ViewID& aScrollId, const nsString& aEvent);
+
+  /* Notify content that the repaint flush is complete. */
+  static void NotifyFlushComplete(PresShell* aPresShell);
+
+  static void NotifyAsyncScrollbarDragInitiated(
+      uint64_t aDragBlockId, const ScrollableLayerGuid::ViewID& aScrollId,
+      ScrollDirection aDirection);
+  static void NotifyAsyncScrollbarDragRejected(
+      const ScrollableLayerGuid::ViewID& aScrollId);
+  static void NotifyAsyncAutoscrollRejected(
+      const ScrollableLayerGuid::ViewID& aScrollId);
+
+  static void CancelAutoscroll(const ScrollableLayerGuid::ViewID& aScrollId);
+  static void NotifyScaleGestureComplete(const nsCOMPtr<nsIWidget>& aWidget,
+                                         float aScale);
+
+  /*
+   * Check if the scrollable frame is currently in the middle of a main thread
+   * async or smooth scroll, or has already requested some other apz scroll that
+   * hasn't been acknowledged by apz.
+   *
+   * We want to discard apz updates to the main-thread scroll offset if this is
+   * true to prevent clobbering higher priority origins.
+   */
+  static bool IsScrollInProgress(nsIScrollableFrame* aFrame);
+
+  /* Notify content of the progress of a pinch gesture that APZ won't do
+   * zooming for (because the apz.allow_zooming pref is false). This function
+   * will dispatch appropriate WidgetSimpleGestureEvent events to gecko.
+   */
+  static void NotifyPinchGesture(PinchGestureInput::PinchGestureType aType,
+                                 const LayoutDevicePoint& aFocusPoint,
+                                 LayoutDeviceCoord aSpanChange,
+                                 Modifiers aModifiers,
+                                 const nsCOMPtr<nsIWidget>& aWidget);
+
+ private:
+  static uint64_t sLastTargetAPZCNotificationInputBlock;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_APZCCallbackHelper_h */
diff --git a/gfx/layers/apz/util/APZEventState.cpp b/gfx/layers/apz/util/APZEventState.cpp
new file mode 100644
index 0000000000..c2bf624dda
--- /dev/null
+++ b/gfx/layers/apz/util/APZEventState.cpp
@@ -0,0 +1,603 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "APZEventState.h"
+
+#include <utility>
+
+#include "APZCCallbackHelper.h"
+#include "ActiveElementManager.h"
+#include "TouchManager.h"
+#include "mozilla/BasicEvents.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/IntegerPrintfMacros.h"
+#include "mozilla/PositionedEventTargeting.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StaticPrefs_ui.h"
+#include "mozilla/ToString.h"
+#include "mozilla/TouchEvents.h"
+#include "mozilla/ViewportUtils.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/dom/MouseEventBinding.h"
+#include "mozilla/layers/APZCCallbackHelper.h"
+#include "mozilla/layers/IAPZCTreeManager.h"
+#include "mozilla/widget/nsAutoRollup.h"
+#include "nsCOMPtr.h"
+#include "nsDocShell.h"
+#include "nsIDOMWindowUtils.h"
+#include "nsINamed.h"
+#include "nsIScrollableFrame.h"
+#include "nsIScrollbarMediator.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsIWidget.h"
+#include "nsLayoutUtils.h"
+#include "nsQueryFrame.h"
+
+static mozilla::LazyLogModule sApzEvtLog("apz.eventstate");
+#define APZES_LOG(...) MOZ_LOG(sApzEvtLog, LogLevel::Debug, (__VA_ARGS__))
+
+// Static helper functions
+namespace {
+
+int32_t WidgetModifiersToDOMModifiers(mozilla::Modifiers aModifiers) {
+  int32_t result = 0;
+  if (aModifiers & mozilla::MODIFIER_SHIFT) {
+    result |= nsIDOMWindowUtils::MODIFIER_SHIFT;
+  }
+  if (aModifiers & mozilla::MODIFIER_CONTROL) {
+    result |= nsIDOMWindowUtils::MODIFIER_CONTROL;
+  }
+  if (aModifiers & mozilla::MODIFIER_ALT) {
+    result |= nsIDOMWindowUtils::MODIFIER_ALT;
+  }
+  if (aModifiers & mozilla::MODIFIER_META) {
+    result |= nsIDOMWindowUtils::MODIFIER_META;
+  }
+  if (aModifiers & mozilla::MODIFIER_ALTGRAPH) {
+    result |= nsIDOMWindowUtils::MODIFIER_ALTGRAPH;
+  }
+  if (aModifiers & mozilla::MODIFIER_CAPSLOCK) {
+    result |= nsIDOMWindowUtils::MODIFIER_CAPSLOCK;
+  }
+  if (aModifiers & mozilla::MODIFIER_FN) {
+    result |= nsIDOMWindowUtils::MODIFIER_FN;
+  }
+  if (aModifiers & mozilla::MODIFIER_FNLOCK) {
+    result |= nsIDOMWindowUtils::MODIFIER_FNLOCK;
+  }
+  if (aModifiers & mozilla::MODIFIER_NUMLOCK) {
+    result |= nsIDOMWindowUtils::MODIFIER_NUMLOCK;
+  }
+  if (aModifiers & mozilla::MODIFIER_SCROLLLOCK) {
+    result |= nsIDOMWindowUtils::MODIFIER_SCROLLLOCK;
+  }
+  if (aModifiers & mozilla::MODIFIER_SYMBOL) {
+    result |= nsIDOMWindowUtils::MODIFIER_SYMBOL;
+  }
+  if (aModifiers & mozilla::MODIFIER_SYMBOLLOCK) {
+    result |= nsIDOMWindowUtils::MODIFIER_SYMBOLLOCK;
+  }
+  if (aModifiers & mozilla::MODIFIER_OS) {
+    result |= nsIDOMWindowUtils::MODIFIER_OS;
+  }
+  return result;
+}
+
+}  // namespace
+
+namespace mozilla {
+namespace layers {
+
+APZEventState::APZEventState(nsIWidget* aWidget,
+                             ContentReceivedInputBlockCallback&& aCallback)
+    : mWidget(nullptr)  // initialized in constructor body
+      ,
+      mActiveElementManager(new ActiveElementManager()),
+      mContentReceivedInputBlockCallback(std::move(aCallback)),
+      mPendingTouchPreventedResponse(false),
+      mPendingTouchPreventedBlockId(0),
+      mEndTouchIsClick(false),
+      mFirstTouchCancelled(false),
+      mTouchEndCancelled(false),
+      mSingleTapsPendingTargetInfo(),
+      mLastTouchIdentifier(0) {
+  nsresult rv;
+  mWidget = do_GetWeakReference(aWidget, &rv);
+  MOZ_ASSERT(NS_SUCCEEDED(rv),
+             "APZEventState constructed with a widget that"
+             " does not support weak references. APZ will NOT work!");
+}
+
+APZEventState::~APZEventState() = default;
+
+RefPtr<DelayedFireSingleTapEvent> DelayedFireSingleTapEvent::Create(
+    Maybe<SingleTapTargetInfo>&& aTargetInfo) {
+  nsCOMPtr<nsITimer> timer = NS_NewTimer();
+  RefPtr<DelayedFireSingleTapEvent> event =
+      new DelayedFireSingleTapEvent(std::move(aTargetInfo), timer);
+  nsresult rv = timer->InitWithCallback(
+      event, StaticPrefs::ui_touch_activation_duration_ms(),
+      nsITimer::TYPE_ONE_SHOT);
+  if (NS_FAILED(rv)) {
+    event->ClearTimer();
+    event = nullptr;
+  }
+  return event;
+}
+
+NS_IMETHODIMP DelayedFireSingleTapEvent::Notify(nsITimer*) {
+  APZES_LOG("DelayedFireSingeTapEvent notification ready=%d",
+            mTargetInfo.isSome());
+  // If the required information to fire the synthesized events has not
+  // been populated yet, we have not received the touch-end. In this case
+  // we should not fire the synthesized events here. The synthesized events
+  // will be fired on touch-end in this case.
+  if (mTargetInfo.isSome()) {
+    FireSingleTapEvent();
+  }
+  mTimer = nullptr;
+  return NS_OK;
+}
+
+NS_IMETHODIMP DelayedFireSingleTapEvent::GetName(nsACString& aName) {
+  aName.AssignLiteral("DelayedFireSingleTapEvent");
+  return NS_OK;
+}
+
+void DelayedFireSingleTapEvent::PopulateTargetInfo(
+    SingleTapTargetInfo&& aTargetInfo) {
+  MOZ_ASSERT(!mTargetInfo.isSome());
+  mTargetInfo = Some(std::move(aTargetInfo));
+  // If the timer no longer exists, we have surpassed the minimum elapsed
+  // time to delay the synthesized click. We can immediately fire the
+  // synthesized events in this case.
+  if (!mTimer) {
+    FireSingleTapEvent();
+  }
+}
+
+void DelayedFireSingleTapEvent::FireSingleTapEvent() {
+  MOZ_ASSERT(mTargetInfo.isSome());
+  nsCOMPtr<nsIWidget> widget = do_QueryReferent(mTargetInfo->mWidget);
+  if (widget) {
+    widget::nsAutoRollup rollup(mTargetInfo->mTouchRollup.get());
+    APZCCallbackHelper::FireSingleTapEvent(mTargetInfo->mPoint,
+                                           mTargetInfo->mModifiers,
+                                           mTargetInfo->mClickCount, widget);
+  }
+}
+
+NS_IMPL_ISUPPORTS(DelayedFireSingleTapEvent, nsITimerCallback, nsINamed)
+
+void APZEventState::ProcessSingleTap(const CSSPoint& aPoint,
+                                     const CSSToLayoutDeviceScale& aScale,
+                                     Modifiers aModifiers, int32_t aClickCount,
+                                     uint64_t aInputBlockId) {
+  APZES_LOG("Handling single tap at %s with %d\n", ToString(aPoint).c_str(),
+            mTouchEndCancelled);
+
+  RefPtr<nsIContent> touchRollup = GetTouchRollup();
+  mTouchRollup = nullptr;
+
+  nsCOMPtr<nsIWidget> widget = GetWidget();
+  if (!widget) {
+    return;
+  }
+
+  if (mTouchEndCancelled) {
+    return;
+  }
+
+  SingleTapTargetInfo targetInfo(mWidget, aPoint * aScale, aModifiers,
+                                 aClickCount, touchRollup);
+
+  auto delayedEvent = mSingleTapsPendingTargetInfo.find(aInputBlockId);
+  if (delayedEvent != mSingleTapsPendingTargetInfo.end()) {
+    APZES_LOG("Found tap for block=%" PRIu64, aInputBlockId);
+
+    // With the target info populated, the event will be fired as
+    // soon as the delay timer expires (or now, if it has already expired).
+    delayedEvent->second->PopulateTargetInfo(std::move(targetInfo));
+    mSingleTapsPendingTargetInfo.erase(delayedEvent);
+  } else {
+    APZES_LOG("Scheduling timer for click event\n");
+
+    // We don't need to keep a reference to the event, because the
+    // event and its timer keep each other alive until the timer expires
+    DelayedFireSingleTapEvent::Create(Some(std::move(targetInfo)));
+  }
+}
+
+PreventDefaultResult APZEventState::FireContextmenuEvents(
+    PresShell* aPresShell, const CSSPoint& aPoint,
+    const CSSToLayoutDeviceScale& aScale, Modifiers aModifiers,
+    const nsCOMPtr<nsIWidget>& aWidget) {
+  // Suppress retargeting for mouse events generated by a long-press
+  EventRetargetSuppression suppression;
+
+  // Synthesize mousemove event for allowing users to emulate to move mouse
+  // cursor over the element.  As a result, users can open submenu UI which
+  // is opened when mouse cursor is moved over a link (i.e., it's a case that
+  // users cannot stay in the page after tapping it).  So, this improves
+  // accessibility in websites which are designed for desktop.
+  // Note that we don't need to check whether mousemove event is consumed or
+  // not because Chrome also ignores the result.
+  APZCCallbackHelper::DispatchSynthesizedMouseEvent(
+      eMouseMove, aPoint * aScale, aModifiers, 0 /* clickCount */, aWidget);
+
+  // Converting the modifiers to DOM format for the DispatchMouseEvent call
+  // is the most useless thing ever because nsDOMWindowUtils::SendMouseEvent
+  // just converts them back to widget format, but that API has many callers,
+  // including in JS code, so it's not trivial to change.
+  CSSPoint point = CSSPoint::FromAppUnits(
+      ViewportUtils::VisualToLayout(CSSPoint::ToAppUnits(aPoint), aPresShell));
+  PreventDefaultResult preventDefaultResult =
+      APZCCallbackHelper::DispatchMouseEvent(
+          aPresShell, u"contextmenu"_ns, point, 2, 1,
+          WidgetModifiersToDOMModifiers(aModifiers),
+          dom::MouseEvent_Binding::MOZ_SOURCE_TOUCH,
+          0 /* Use the default value here. */);
+
+  APZES_LOG("Contextmenu event %s\n", ToString(preventDefaultResult).c_str());
+  if (preventDefaultResult != PreventDefaultResult::No) {
+    // If the contextmenu event was handled then we're showing a contextmenu,
+    // and so we should remove any activation
+    mActiveElementManager->ClearActivation();
+#ifndef XP_WIN
+  } else {
+    // If the contextmenu wasn't consumed, fire the eMouseLongTap event.
+    nsEventStatus status = APZCCallbackHelper::DispatchSynthesizedMouseEvent(
+        eMouseLongTap, aPoint * aScale, aModifiers,
+        /*clickCount*/ 1, aWidget);
+    if (status == nsEventStatus_eConsumeNoDefault) {
+      // Assuming no JS actor listens eMouseLongTap events.
+      preventDefaultResult = PreventDefaultResult::ByContent;
+    } else {
+      preventDefaultResult = PreventDefaultResult::No;
+    }
+    APZES_LOG("eMouseLongTap event %s\n",
+              ToString(preventDefaultResult).c_str());
+#endif
+  }
+
+  return preventDefaultResult;
+}
+
+void APZEventState::ProcessLongTap(PresShell* aPresShell,
+                                   const CSSPoint& aPoint,
+                                   const CSSToLayoutDeviceScale& aScale,
+                                   Modifiers aModifiers,
+                                   uint64_t aInputBlockId) {
+  APZES_LOG("Handling long tap at %s\n", ToString(aPoint).c_str());
+
+  nsCOMPtr<nsIWidget> widget = GetWidget();
+  if (!widget) {
+    return;
+  }
+
+  SendPendingTouchPreventedResponse(false);
+
+#ifdef XP_WIN
+  // On Windows, we fire the contextmenu events when the user lifts their
+  // finger, in keeping with the platform convention. This happens in the
+  // ProcessLongTapUp function. However, we still fire the eMouseLongTap event
+  // at this time, because things like text selection or dragging may want
+  // to know about it.
+  nsEventStatus status = APZCCallbackHelper::DispatchSynthesizedMouseEvent(
+      eMouseLongTap, aPoint * aScale, aModifiers, /*clickCount*/ 1, widget);
+
+  PreventDefaultResult preventDefaultResult =
+      (status == nsEventStatus_eConsumeNoDefault)
+          ? PreventDefaultResult::ByContent
+          : PreventDefaultResult::No;
+#else
+  PreventDefaultResult preventDefaultResult =
+      FireContextmenuEvents(aPresShell, aPoint, aScale, aModifiers, widget);
+#endif
+  mContentReceivedInputBlockCallback(
+      aInputBlockId, preventDefaultResult != PreventDefaultResult::No);
+
+  const bool eventHandled =
+#ifdef MOZ_WIDGET_ANDROID
+      // On Android, GeckoView calls preventDefault() in a JSActor
+      // (ContentDelegateChild.jsm) when opening context menu so that we can
+      // tell whether contextmenu opens in response to the contextmenu event by
+      // checking where preventDefault() got called.
+      preventDefaultResult == PreventDefaultResult::ByChrome;
+#else
+      // Unfortunately on desktop platforms other than Windows we can't use
+      // the same approach for Android since we no longer call preventDefault()
+      // since bug 1558506. So for now, we keep the current behavior that is
+      // sending a touchcancel event if the contextmenu event was
+      // preventDefault-ed in an event handler in the content itself.
+      preventDefaultResult == PreventDefaultResult::ByContent;
+#endif
+  if (eventHandled) {
+    // Also send a touchcancel to content
+    //  a) on Android if browser's contextmenu is open
+    //  b) on Windows if the long tap event was consumed
+    //  c) on other platforms if preventDefault() was called for the contextmenu
+    //     event
+    // so that listeners that might be waiting for a touchend don't trigger.
+    WidgetTouchEvent cancelTouchEvent(true, eTouchCancel, widget.get());
+    cancelTouchEvent.mModifiers = aModifiers;
+    auto ldPoint = LayoutDeviceIntPoint::Round(aPoint * aScale);
+    cancelTouchEvent.mTouches.AppendElement(new mozilla::dom::Touch(
+        mLastTouchIdentifier, ldPoint, LayoutDeviceIntPoint(), 0, 0));
+    APZCCallbackHelper::DispatchWidgetEvent(cancelTouchEvent);
+  }
+}
+
+void APZEventState::ProcessLongTapUp(PresShell* aPresShell,
+                                     const CSSPoint& aPoint,
+                                     const CSSToLayoutDeviceScale& aScale,
+                                     Modifiers aModifiers) {
+#ifdef XP_WIN
+  nsCOMPtr<nsIWidget> widget = GetWidget();
+  if (widget) {
+    FireContextmenuEvents(aPresShell, aPoint, aScale, aModifiers, widget);
+  }
+#endif
+}
+
+void APZEventState::ProcessTouchEvent(
+    const WidgetTouchEvent& aEvent, const ScrollableLayerGuid& aGuid,
+    uint64_t aInputBlockId, nsEventStatus aApzResponse,
+    nsEventStatus aContentResponse,
+    nsTArray<TouchBehaviorFlags>&& aAllowedTouchBehaviors) {
+  if (aEvent.mMessage == eTouchStart && aEvent.mTouches.Length() > 0) {
+    mActiveElementManager->SetTargetElement(
+        aEvent.mTouches[0]->GetOriginalTarget());
+    mLastTouchIdentifier = aEvent.mTouches[0]->Identifier();
+  }
+  if (aEvent.mMessage == eTouchStart) {
+    // We get the allowed touch behaviors on a touchstart, but may not actually
+    // use them until the first touchmove, so we stash them in a member
+    // variable.
+    mTouchBlockAllowedBehaviors = std::move(aAllowedTouchBehaviors);
+  }
+
+  bool isTouchPrevented = aContentResponse == nsEventStatus_eConsumeNoDefault;
+  bool sentContentResponse = false;
+  APZES_LOG("Handling event type %d isPrevented=%d\n", aEvent.mMessage,
+            isTouchPrevented);
+  switch (aEvent.mMessage) {
+    case eTouchStart: {
+      mTouchEndCancelled = false;
+      mTouchRollup = do_GetWeakReference(widget::nsAutoRollup::GetLastRollup());
+
+      SendPendingTouchPreventedResponse(false);
+      // The above call may have sent a message to APZ if we get two
+      // TOUCH_STARTs in a row and just responded to the first one.
+
+      // We're about to send a response back to APZ, but we should only do it
+      // for events that went through APZ (which should be all of them).
+      MOZ_ASSERT(aEvent.mFlags.mHandledByAPZ);
+
+      // If the first touchstart event was preventDefaulted, ensure that any
+      // subsequent additional touchstart events also get preventDefaulted. This
+      // ensures that e.g. pinch zooming is prevented even if just the first
+      // touchstart was prevented by content.
+      if (mTouchCounter.GetActiveTouchCount() == 0) {
+        mFirstTouchCancelled = isTouchPrevented;
+      } else {
+        if (mFirstTouchCancelled && !isTouchPrevented) {
+          APZES_LOG(
+              "Propagating prevent-default from first-touch for block %" PRIu64
+              "\n",
+              aInputBlockId);
+        }
+        isTouchPrevented |= mFirstTouchCancelled;
+      }
+
+      if (isTouchPrevented) {
+        mContentReceivedInputBlockCallback(aInputBlockId, isTouchPrevented);
+        sentContentResponse = true;
+      } else {
+        APZES_LOG("Event not prevented; pending response for %" PRIu64 " %s\n",
+                  aInputBlockId, ToString(aGuid).c_str());
+        mPendingTouchPreventedResponse = true;
+        mPendingTouchPreventedGuid = aGuid;
+        mPendingTouchPreventedBlockId = aInputBlockId;
+      }
+      break;
+    }
+
+    case eTouchEnd:
+      if (isTouchPrevented) {
+        mTouchEndCancelled = true;
+        mEndTouchIsClick = false;
+      }
+      [[fallthrough]];
+    case eTouchCancel:
+      mActiveElementManager->HandleTouchEndEvent(mEndTouchIsClick);
+      [[fallthrough]];
+    case eTouchMove: {
+      if (mPendingTouchPreventedResponse) {
+        MOZ_ASSERT(aGuid == mPendingTouchPreventedGuid);
+      }
+      sentContentResponse = SendPendingTouchPreventedResponse(isTouchPrevented);
+      break;
+    }
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unknown touch event type");
+      break;
+  }
+
+  mTouchCounter.Update(aEvent);
+  if (mTouchCounter.GetActiveTouchCount() == 0) {
+    mFirstTouchCancelled = false;
+  }
+
+  APZES_LOG("Pointercancel if %d %d %d %d\n", sentContentResponse,
+            !isTouchPrevented, aApzResponse == nsEventStatus_eConsumeDoDefault,
+            MainThreadAgreesEventsAreConsumableByAPZ());
+  if (sentContentResponse && !isTouchPrevented &&
+      aApzResponse == nsEventStatus_eConsumeDoDefault &&
+      MainThreadAgreesEventsAreConsumableByAPZ()) {
+    WidgetTouchEvent cancelEvent(aEvent);
+    cancelEvent.mMessage = eTouchPointerCancel;
+    cancelEvent.mFlags.mCancelable = false;  // mMessage != eTouchCancel;
+    for (uint32_t i = 0; i < cancelEvent.mTouches.Length(); ++i) {
+      if (mozilla::dom::Touch* touch = cancelEvent.mTouches[i]) {
+        touch->convertToPointer = true;
+      }
+    }
+    nsEventStatus status;
+    cancelEvent.mWidget->DispatchEvent(&cancelEvent, status);
+  }
+}
+
+bool APZEventState::MainThreadAgreesEventsAreConsumableByAPZ() const {
+  // APZ errs on the side of saying it can consume touch events to perform
+  // default user-agent behaviours. In particular it may say this if it hasn't
+  // received accurate touch-action information. Here we double-check using
+  // accurate touch-action information. This code is kinda-sorta the main
+  // thread equivalent of AsyncPanZoomController::ArePointerEventsConsumable().
+
+  switch (mTouchBlockAllowedBehaviors.Length()) {
+    case 0:
+      // If we don't have any touch-action (e.g. because it is disabled) then
+      // APZ has no restrictions.
+      return true;
+
+    case 1: {
+      // If there's one touch point in this touch block, then check the pan-x
+      // and pan-y flags. If neither is allowed, then we disagree with APZ and
+      // say that it can't do anything with this touch block. Note that it would
+      // be even better if we could check the allowed scroll directions of the
+      // scrollframe at this point and refine this further.
+      TouchBehaviorFlags flags = mTouchBlockAllowedBehaviors[0];
+      return (flags & AllowedTouchBehavior::HORIZONTAL_PAN) ||
+             (flags & AllowedTouchBehavior::VERTICAL_PAN);
+    }
+
+    case 2: {
+      // If there's two touch points in this touch block, check that they both
+      // allow zooming.
+      for (const auto& allowed : mTouchBlockAllowedBehaviors) {
+        if (!(allowed & AllowedTouchBehavior::PINCH_ZOOM)) {
+          return false;
+        }
+      }
+      return true;
+    }
+
+    default:
+      // More than two touch points? APZ shouldn't be doing anything with this,
+      // so APZ shouldn't be consuming them.
+      return false;
+  }
+}
+
+void APZEventState::ProcessWheelEvent(const WidgetWheelEvent& aEvent,
+                                      uint64_t aInputBlockId) {
+  // If this event starts a swipe, indicate that it shouldn't result in a
+  // scroll by setting defaultPrevented to true.
+  bool defaultPrevented = aEvent.DefaultPrevented() || aEvent.TriggersSwipe();
+  mContentReceivedInputBlockCallback(aInputBlockId, defaultPrevented);
+}
+
+void APZEventState::ProcessMouseEvent(const WidgetMouseEvent& aEvent,
+                                      uint64_t aInputBlockId) {
+  bool defaultPrevented = false;
+  mContentReceivedInputBlockCallback(aInputBlockId, defaultPrevented);
+}
+
+void APZEventState::ProcessAPZStateChange(ViewID aViewId,
+                                          APZStateChange aChange, int aArg,
+                                          Maybe<uint64_t> aInputBlockId) {
+  switch (aChange) {
+    case APZStateChange::eTransformBegin: {
+      nsIScrollableFrame* sf = nsLayoutUtils::FindScrollableFrameFor(aViewId);
+      if (sf) {
+        sf->SetTransformingByAPZ(true);
+        sf->ScrollbarActivityStarted();
+      }
+
+      nsIContent* content = nsLayoutUtils::FindContentFor(aViewId);
+      dom::Document* doc = content ? content->GetComposedDoc() : nullptr;
+      nsCOMPtr<nsIDocShell> docshell(doc ? doc->GetDocShell() : nullptr);
+      if (docshell && sf) {
+        nsDocShell* nsdocshell = static_cast<nsDocShell*>(docshell.get());
+        nsdocshell->NotifyAsyncPanZoomStarted();
+      }
+      break;
+    }
+    case APZStateChange::eTransformEnd: {
+      nsIScrollableFrame* sf = nsLayoutUtils::FindScrollableFrameFor(aViewId);
+      if (sf) {
+        sf->SetTransformingByAPZ(false);
+        sf->ScrollbarActivityStopped();
+      }
+
+      nsIContent* content = nsLayoutUtils::FindContentFor(aViewId);
+      dom::Document* doc = content ? content->GetComposedDoc() : nullptr;
+      nsCOMPtr<nsIDocShell> docshell(doc ? doc->GetDocShell() : nullptr);
+      if (docshell && sf) {
+        nsDocShell* nsdocshell = static_cast<nsDocShell*>(docshell.get());
+        nsdocshell->NotifyAsyncPanZoomStopped();
+      }
+      break;
+    }
+    case APZStateChange::eStartTouch: {
+      bool canBePan = aArg;
+      mActiveElementManager->HandleTouchStart(canBePan);
+      // If this is a non-scrollable content, set a timer for the amount of
+      // time specified by ui.touch_activation.duration_ms to fire the
+      // synthesized click and mouse events.
+      APZES_LOG("%s: can-be-pan=%d", __FUNCTION__, aArg);
+      if (!canBePan) {
+        MOZ_ASSERT(aInputBlockId.isSome());
+        RefPtr<DelayedFireSingleTapEvent> delayedEvent =
+            DelayedFireSingleTapEvent::Create(Nothing());
+        DebugOnly<bool> insertResult =
+            mSingleTapsPendingTargetInfo.emplace(*aInputBlockId, delayedEvent)
+                .second;
+        MOZ_ASSERT(insertResult, "Failed to insert delayed tap event.");
+      }
+      break;
+    }
+    case APZStateChange::eStartPanning: {
+      // The user started to pan, so we don't want anything to be :active.
+      mActiveElementManager->ClearActivation();
+      break;
+    }
+    case APZStateChange::eEndTouch: {
+      mEndTouchIsClick = aArg;
+      mActiveElementManager->HandleTouchEnd();
+      break;
+    }
+  }
+}
+
+bool APZEventState::SendPendingTouchPreventedResponse(bool aPreventDefault) {
+  if (mPendingTouchPreventedResponse) {
+    APZES_LOG("Sending response %d for pending guid: %s\n", aPreventDefault,
+              ToString(mPendingTouchPreventedGuid).c_str());
+    mContentReceivedInputBlockCallback(mPendingTouchPreventedBlockId,
+                                       aPreventDefault);
+    mPendingTouchPreventedResponse = false;
+    return true;
+  }
+  return false;
+}
+
+already_AddRefed<nsIWidget> APZEventState::GetWidget() const {
+  nsCOMPtr<nsIWidget> result = do_QueryReferent(mWidget);
+  return result.forget();
+}
+
+already_AddRefed<nsIContent> APZEventState::GetTouchRollup() const {
+  nsCOMPtr<nsIContent> result = do_QueryReferent(mTouchRollup);
+  return result.forget();
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/APZEventState.h b/gfx/layers/apz/util/APZEventState.h
new file mode 100644
index 0000000000..e4f6c98303
--- /dev/null
+++ b/gfx/layers/apz/util/APZEventState.h
@@ -0,0 +1,190 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_APZEventState_h
+#define mozilla_layers_APZEventState_h
+
+#include <stdint.h>
+
+#include "Units.h"
+#include "mozilla/EventForwards.h"
+#include "mozilla/layers/GeckoContentControllerTypes.h"  // for APZStateChange
+#include "mozilla/layers/ScrollableLayerGuid.h"  // for ScrollableLayerGuid
+#include "mozilla/layers/TouchCounter.h"         // for TouchCounter
+#include "mozilla/RefPtr.h"
+#include "mozilla/StaticPrefs_ui.h"
+#include "nsCOMPtr.h"
+#include "nsISupportsImpl.h"  // for NS_INLINE_DECL_REFCOUNTING
+#include "nsITimer.h"
+#include "nsIWeakReferenceUtils.h"  // for nsWeakPtr
+
+#include <functional>
+#include <unordered_map>
+
+template <class>
+class nsCOMPtr;
+class nsIContent;
+class nsIWidget;
+
+namespace mozilla {
+
+class PresShell;
+enum class PreventDefaultResult : uint8_t;
+
+namespace layers {
+
+class ActiveElementManager;
+
+typedef std::function<void(uint64_t /* input block id */,
+                           bool /* prevent default */)>
+    ContentReceivedInputBlockCallback;
+
+struct SingleTapTargetInfo {
+  nsWeakPtr mWidget;
+  LayoutDevicePoint mPoint;
+  Modifiers mModifiers;
+  int32_t mClickCount;
+  RefPtr<nsIContent> mTouchRollup;
+
+  explicit SingleTapTargetInfo(nsWeakPtr aWidget, LayoutDevicePoint aPoint,
+                               Modifiers aModifiers, int32_t aClickCount,
+                               RefPtr<nsIContent> aTouchRollup)
+      : mWidget(std::move(aWidget)),
+        mPoint(aPoint),
+        mModifiers(aModifiers),
+        mClickCount(aClickCount),
+        mTouchRollup(std::move(aTouchRollup)) {}
+
+  SingleTapTargetInfo(SingleTapTargetInfo&&) = default;
+  SingleTapTargetInfo& operator=(SingleTapTargetInfo&&) = default;
+};
+
+class DelayedFireSingleTapEvent final : public nsITimerCallback,
+                                        public nsINamed {
+ private:
+  explicit DelayedFireSingleTapEvent(Maybe<SingleTapTargetInfo>&& aTargetInfo,
+                                     const nsCOMPtr<nsITimer>& aTimer)
+      : mTargetInfo(std::move(aTargetInfo))
+        // Hold the reference count until we are called back.
+        ,
+        mTimer(aTimer) {}
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  static RefPtr<DelayedFireSingleTapEvent> Create(
+      Maybe<SingleTapTargetInfo>&& aTargetInfo);
+
+  NS_IMETHOD Notify(nsITimer*) override;
+
+  NS_IMETHOD GetName(nsACString& aName) override;
+
+  void PopulateTargetInfo(SingleTapTargetInfo&& aTargetInfo);
+
+  void FireSingleTapEvent();
+
+  void ClearTimer() { mTimer = nullptr; }
+
+ private:
+  ~DelayedFireSingleTapEvent() = default;
+
+  Maybe<SingleTapTargetInfo> mTargetInfo;
+  nsCOMPtr<nsITimer> mTimer;
+};
+
+/**
+ * A content-side component that keeps track of state for handling APZ
+ * gestures and sending APZ notifications.
+ */
+class APZEventState final {
+  typedef GeckoContentController_APZStateChange APZStateChange;
+  typedef ScrollableLayerGuid::ViewID ViewID;
+
+ public:
+  APZEventState(nsIWidget* aWidget,
+                ContentReceivedInputBlockCallback&& aCallback);
+
+  NS_INLINE_DECL_REFCOUNTING(APZEventState);
+
+  void ProcessSingleTap(const CSSPoint& aPoint,
+                        const CSSToLayoutDeviceScale& aScale,
+                        Modifiers aModifiers, int32_t aClickCount,
+                        uint64_t aInputBlockId);
+  MOZ_CAN_RUN_SCRIPT
+  void ProcessLongTap(PresShell* aPresShell, const CSSPoint& aPoint,
+                      const CSSToLayoutDeviceScale& aScale,
+                      Modifiers aModifiers, uint64_t aInputBlockId);
+  MOZ_CAN_RUN_SCRIPT
+  void ProcessLongTapUp(PresShell* aPresShell, const CSSPoint& aPoint,
+                        const CSSToLayoutDeviceScale& aScale,
+                        Modifiers aModifiers);
+  void ProcessTouchEvent(const WidgetTouchEvent& aEvent,
+                         const ScrollableLayerGuid& aGuid,
+                         uint64_t aInputBlockId, nsEventStatus aApzResponse,
+                         nsEventStatus aContentResponse,
+                         nsTArray<TouchBehaviorFlags>&& aAllowedTouchBehaviors);
+  void ProcessWheelEvent(const WidgetWheelEvent& aEvent,
+                         uint64_t aInputBlockId);
+  void ProcessMouseEvent(const WidgetMouseEvent& aEvent,
+                         uint64_t aInputBlockId);
+  void ProcessAPZStateChange(ViewID aViewId, APZStateChange aChange, int aArg,
+                             Maybe<uint64_t> aInputBlockId);
+
+ private:
+  ~APZEventState();
+  bool SendPendingTouchPreventedResponse(bool aPreventDefault);
+  MOZ_CAN_RUN_SCRIPT
+  PreventDefaultResult FireContextmenuEvents(
+      PresShell* aPresShell, const CSSPoint& aPoint,
+      const CSSToLayoutDeviceScale& aScale, Modifiers aModifiers,
+      const nsCOMPtr<nsIWidget>& aWidget);
+  already_AddRefed<nsIWidget> GetWidget() const;
+  already_AddRefed<nsIContent> GetTouchRollup() const;
+  bool MainThreadAgreesEventsAreConsumableByAPZ() const;
+
+ private:
+  nsWeakPtr mWidget;
+  RefPtr<ActiveElementManager> mActiveElementManager;
+  ContentReceivedInputBlockCallback mContentReceivedInputBlockCallback;
+  TouchCounter mTouchCounter;
+  bool mPendingTouchPreventedResponse;
+  ScrollableLayerGuid mPendingTouchPreventedGuid;
+  uint64_t mPendingTouchPreventedBlockId;
+  bool mEndTouchIsClick;
+  bool mFirstTouchCancelled;
+  bool mTouchEndCancelled;
+
+  // Store pending single tap event dispatch tasks keyed on the
+  // tap gesture's input block id. In the case where multiple taps
+  // occur in quick succession, we may receive a later tap while the
+  // dispatch for an earlier tap is still pending.
+  std::unordered_map<uint64_t, RefPtr<DelayedFireSingleTapEvent>>
+      mSingleTapsPendingTargetInfo;
+
+  int32_t mLastTouchIdentifier;
+  nsTArray<TouchBehaviorFlags> mTouchBlockAllowedBehaviors;
+
+  // Because touch-triggered mouse events (e.g. mouse events from a tap
+  // gesture) happen asynchronously from the touch events themselves, we
+  // need to stash and replicate some of the state from the touch events
+  // to the mouse events. One piece of state is the rollup content, which
+  // is the content for which a popup window was recently closed. If we
+  // don't replicate this state properly during the mouse events, the
+  // synthetic click might reopen a popup window that was just closed by
+  // the touch event, which is undesirable. See also documentation in
+  // nsAutoRollup.h
+  // Note that in cases where we get multiple touch blocks interleaved with
+  // their single-tap event notifications, mTouchRollup may hold an incorrect
+  // value. This is kind of an edge case, and falls in the same category of
+  // problems as bug 1227241. I intend that fixing that bug will also take
+  // care of this potential problem.
+  nsWeakPtr mTouchRollup;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_APZEventState_h */
diff --git a/gfx/layers/apz/util/APZTaskRunnable.cpp b/gfx/layers/apz/util/APZTaskRunnable.cpp
new file mode 100644
index 0000000000..6192f385a7
--- /dev/null
+++ b/gfx/layers/apz/util/APZTaskRunnable.cpp
@@ -0,0 +1,142 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "APZTaskRunnable.h"
+
+#include "mozilla/PresShell.h"
+#include "nsRefreshDriver.h"
+
+namespace mozilla::layers {
+
+NS_IMETHODIMP
+APZTaskRunnable::Run() {
+  if (!mController) {
+    mRegisteredPresShellId = 0;
+    return NS_OK;
+  }
+
+  // Move these variables first since below RequestContentPaint and
+  // NotifyFlushComplete might spin event loop so that any new incoming requests
+  // will be properly queued and run in the next refresh driver's tick.
+  const bool needsFlushCompleteNotification = mNeedsFlushCompleteNotification;
+  auto requests = std::move(mPendingRepaintRequestQueue);
+  mPendingRepaintRequestMap.clear();
+  mNeedsFlushCompleteNotification = false;
+  mRegisteredPresShellId = 0;
+  RefPtr<GeckoContentController> controller = mController;
+
+  // We need to process pending RepaintRequests first.
+  while (!requests.empty()) {
+    controller->RequestContentRepaint(requests.front());
+    requests.pop_front();
+  }
+
+  if (needsFlushCompleteNotification) {
+    // Then notify "apz-repaints-flushed" so that we can ensure that all pending
+    // scroll position updates have finished when the "apz-repaints-flushed"
+    // arrives.
+    controller->NotifyFlushComplete();
+  }
+
+  return NS_OK;
+}
+
+void APZTaskRunnable::QueueRequest(const RepaintRequest& aRequest) {
+  // If we are in test-controlled refreshes mode, process this |aRequest|
+  // synchronously.
+  if (IsTestControllingRefreshesEnabled()) {
+    // Flush all pending requests and notification just in case the refresh
+    // driver mode was changed before flushing them.
+    RefPtr<GeckoContentController> controller = mController;
+    Run();
+    controller->RequestContentRepaint(aRequest);
+    return;
+  }
+  EnsureRegisterAsEarlyRunner();
+
+  RepaintRequestKey key{aRequest.GetScrollId(), aRequest.GetScrollUpdateType()};
+
+  auto lastDiscardableRequest = mPendingRepaintRequestMap.find(key);
+  // If there's an existing request with the same key, we can discard it and we
+  // push the incoming one into the queue's tail so that we can ensure the order
+  // of processing requests.
+  if (lastDiscardableRequest != mPendingRepaintRequestMap.end()) {
+    for (auto it = mPendingRepaintRequestQueue.begin();
+         it != mPendingRepaintRequestQueue.end(); it++) {
+      if (RepaintRequestKey{it->GetScrollId(), it->GetScrollUpdateType()} ==
+          key) {
+        mPendingRepaintRequestQueue.erase(it);
+        break;
+      }
+    }
+  }
+  mPendingRepaintRequestMap.insert(key);
+  mPendingRepaintRequestQueue.push_back(aRequest);
+}
+
+void APZTaskRunnable::QueueFlushCompleteNotification() {
+  // If we are in test-controlled refreshes mode, notify apz-repaints-flushed
+  // synchronously.
+  if (IsTestControllingRefreshesEnabled()) {
+    // Flush all pending requests and notification just in case the refresh
+    // driver mode was changed before flushing them.
+    RefPtr<GeckoContentController> controller = mController;
+    Run();
+    controller->NotifyFlushComplete();
+    return;
+  }
+
+  EnsureRegisterAsEarlyRunner();
+
+  mNeedsFlushCompleteNotification = true;
+}
+
+bool APZTaskRunnable::IsRegisteredWithCurrentPresShell() const {
+  MOZ_ASSERT(mController);
+
+  uint32_t current = 0;
+  if (PresShell* presShell = mController->GetTopLevelPresShell()) {
+    current = presShell->GetPresShellId();
+  }
+  return mRegisteredPresShellId == current;
+}
+
+void APZTaskRunnable::EnsureRegisterAsEarlyRunner() {
+  if (IsRegisteredWithCurrentPresShell()) {
+    return;
+  }
+
+  // If the registered presshell id has been changed, we need to discard pending
+  // requests and notification since all of them are for documents which
+  // have been torn down.
+  if (mRegisteredPresShellId) {
+    mPendingRepaintRequestMap.clear();
+    mPendingRepaintRequestQueue.clear();
+    mNeedsFlushCompleteNotification = false;
+  }
+
+  if (PresShell* presShell = mController->GetTopLevelPresShell()) {
+    if (nsRefreshDriver* driver = presShell->GetRefreshDriver()) {
+      driver->AddEarlyRunner(this);
+      mRegisteredPresShellId = presShell->GetPresShellId();
+    }
+  }
+}
+
+bool APZTaskRunnable::IsTestControllingRefreshesEnabled() const {
+  if (!mController) {
+    return false;
+  }
+
+  if (PresShell* presShell = mController->GetTopLevelPresShell()) {
+    if (nsRefreshDriver* driver = presShell->GetRefreshDriver()) {
+      return driver->IsTestControllingRefreshesEnabled();
+    }
+  }
+  return false;
+}
+
+}  // namespace mozilla::layers
diff --git a/gfx/layers/apz/util/APZTaskRunnable.h b/gfx/layers/apz/util/APZTaskRunnable.h
new file mode 100644
index 0000000000..f5de21abd4
--- /dev/null
+++ b/gfx/layers/apz/util/APZTaskRunnable.h
@@ -0,0 +1,89 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_RepaintRequestRunnable_h
+#define mozilla_layers_RepaintRequestRunnable_h
+
+#include <deque>
+#include <unordered_set>
+
+#include "mozilla/layers/GeckoContentController.h"
+#include "mozilla/layers/RepaintRequest.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+namespace layers {
+
+class GeckoContentController;
+
+// A runnable invoked in nsRefreshDriver::Tick as an early runnable.
+class APZTaskRunnable final : public Runnable {
+ public:
+  explicit APZTaskRunnable(GeckoContentController* aController)
+      : Runnable("RepaintRequestRunnable"),
+        mController(aController),
+        mRegisteredPresShellId(0),
+        mNeedsFlushCompleteNotification(false) {}
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY NS_DECL_NSIRUNNABLE
+
+      // Queue a RepaintRequest.
+      // If there's already a RepaintRequest having the same scroll id, the old
+      // one will be discarded.
+      void
+      QueueRequest(const RepaintRequest& aRequest);
+  void QueueFlushCompleteNotification();
+  void Revoke() {
+    mController = nullptr;
+    mRegisteredPresShellId = 0;
+  }
+
+ private:
+  void EnsureRegisterAsEarlyRunner();
+  bool IsRegisteredWithCurrentPresShell() const;
+  bool IsTestControllingRefreshesEnabled() const;
+
+  // Use a GeckoContentController raw pointer here since the owner of the
+  // GeckoContentController instance (an APZChild instance) holds a strong
+  // reference of this APZTaskRunnable instance and will call Revoke() before
+  // the GeckoContentController gets destroyed in the dtor of the APZChild
+  // instance.
+  GeckoContentController* mController;
+
+  struct RepaintRequestKey {
+    ScrollableLayerGuid::ViewID mScrollId;
+    RepaintRequest::ScrollOffsetUpdateType mScrollUpdateType;
+    bool operator==(const RepaintRequestKey& aOther) const {
+      return mScrollId == aOther.mScrollId &&
+             mScrollUpdateType == aOther.mScrollUpdateType;
+    }
+    struct HashFn {
+      std::size_t operator()(const RepaintRequestKey& aKey) const {
+        return HashGeneric(aKey.mScrollId, aKey.mScrollUpdateType);
+      }
+    };
+  };
+  using RepaintRequests =
+      std::unordered_set<RepaintRequestKey, RepaintRequestKey::HashFn>;
+  // We have an unordered_map and a deque for pending RepaintRequests. The
+  // unordered_map is for quick lookup and the deque is for processing the
+  // pending RepaintRequests in the order we queued.
+  RepaintRequests mPendingRepaintRequestMap;
+  std::deque<RepaintRequest> mPendingRepaintRequestQueue;
+  // This APZTaskRunnable instance is per APZChild instance, which means its
+  // lifetime is tied to the APZChild instance, thus this APZTaskRunnable
+  // instance will be (re-)used for different pres shells so we'd need to
+  // have to remember the pres shell which is currently tied to the APZChild
+  // to deliver queued requests and notifications to the proper pres shell.
+  uint32_t mRegisteredPresShellId;
+  bool mNeedsFlushCompleteNotification;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif  // mozilla_layers_RepaintRequestRunnable_h
diff --git a/gfx/layers/apz/util/APZThreadUtils.cpp b/gfx/layers/apz/util/APZThreadUtils.cpp
new file mode 100644
index 0000000000..d3bf43e61d
--- /dev/null
+++ b/gfx/layers/apz/util/APZThreadUtils.cpp
@@ -0,0 +1,119 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "APZThreadUtils.h"
+
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/ProfilerRunnable.h"
+#include "mozilla/StaticMutex.h"
+
+#include "nsISerialEventTarget.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+
+namespace mozilla {
+namespace layers {
+
+static bool sThreadAssertionsEnabled = true;
+static StaticRefPtr<nsISerialEventTarget> sControllerThread;
+static StaticMutex sControllerThreadMutex MOZ_UNANNOTATED;
+
+/*static*/
+void APZThreadUtils::SetThreadAssertionsEnabled(bool aEnabled) {
+  StaticMutexAutoLock lock(sControllerThreadMutex);
+  sThreadAssertionsEnabled = aEnabled;
+}
+
+/*static*/
+bool APZThreadUtils::GetThreadAssertionsEnabled() {
+  StaticMutexAutoLock lock(sControllerThreadMutex);
+  return sThreadAssertionsEnabled;
+}
+
+/*static*/
+void APZThreadUtils::SetControllerThread(nsISerialEventTarget* aThread) {
+  // We must either be setting the initial controller thread, or removing it,
+  // or re-using an existing controller thread.
+  StaticMutexAutoLock lock(sControllerThreadMutex);
+  MOZ_ASSERT(!sControllerThread || !aThread || sControllerThread == aThread);
+  if (aThread != sControllerThread) {
+    // This can only happen once, on startup.
+    sControllerThread = aThread;
+    ClearOnShutdown(&sControllerThread);
+  }
+}
+
+/*static*/
+void APZThreadUtils::AssertOnControllerThread() {
+#if DEBUG
+  if (!GetThreadAssertionsEnabled()) {
+    return;
+  }
+  StaticMutexAutoLock lock(sControllerThreadMutex);
+  MOZ_ASSERT(sControllerThread && sControllerThread->IsOnCurrentThread());
+#endif
+}
+
+/*static*/
+void APZThreadUtils::RunOnControllerThread(RefPtr<Runnable>&& aTask,
+                                           uint32_t flags) {
+  RefPtr<nsISerialEventTarget> thread;
+  {
+    StaticMutexAutoLock lock(sControllerThreadMutex);
+    thread = sControllerThread;
+  }
+  RefPtr<Runnable> task = std::move(aTask);
+
+  if (!thread) {
+    // Could happen on startup or if Shutdown() got called.
+    NS_WARNING("Dropping task posted to controller thread");
+    return;
+  }
+
+  if (thread->IsOnCurrentThread()) {
+    AUTO_PROFILE_FOLLOWING_RUNNABLE(task);
+    task->Run();
+  } else {
+    thread->Dispatch(task.forget(), flags);
+  }
+}
+
+/*static*/
+bool APZThreadUtils::IsControllerThread() {
+  StaticMutexAutoLock lock(sControllerThreadMutex);
+  return sControllerThread && sControllerThread->IsOnCurrentThread();
+}
+
+/*static*/
+bool APZThreadUtils::IsControllerThreadAlive() {
+  StaticMutexAutoLock lock(sControllerThreadMutex);
+  return !!sControllerThread;
+}
+
+/*static*/
+void APZThreadUtils::DelayedDispatch(already_AddRefed<Runnable> aRunnable,
+                                     int aDelayMs) {
+  MOZ_ASSERT(!XRE_IsContentProcess(),
+             "ContentProcessController should only be used remotely.");
+  RefPtr<nsISerialEventTarget> thread;
+  {
+    StaticMutexAutoLock lock(sControllerThreadMutex);
+    thread = sControllerThread;
+  }
+  if (!thread) {
+    // Could happen on startup
+    NS_WARNING("Dropping task posted to controller thread");
+    return;
+  }
+  if (aDelayMs) {
+    thread->DelayedDispatch(std::move(aRunnable), aDelayMs);
+  } else {
+    thread->Dispatch(std::move(aRunnable));
+  }
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/APZThreadUtils.h b/gfx/layers/apz/util/APZThreadUtils.h
new file mode 100644
index 0000000000..f1560eee8c
--- /dev/null
+++ b/gfx/layers/apz/util/APZThreadUtils.h
@@ -0,0 +1,75 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_APZThreadUtils_h
+#define mozilla_layers_APZThreadUtils_h
+
+#include "nsIEventTarget.h"
+#include "nsINamed.h"
+#include "nsITimer.h"
+#include "nsString.h"
+
+class nsISerialEventTarget;
+
+namespace mozilla {
+
+class Runnable;
+
+namespace layers {
+
+class APZThreadUtils {
+ public:
+  /**
+   * In the gtest environment everything runs on one thread, so we
+   * shouldn't assert that we're on a particular thread. This enables
+   * that behaviour.
+   */
+  static void SetThreadAssertionsEnabled(bool aEnabled);
+  static bool GetThreadAssertionsEnabled();
+
+  /**
+   * Set the controller thread.
+   */
+  static void SetControllerThread(nsISerialEventTarget* aThread);
+
+  /**
+   * This can be used to assert that the current thread is the
+   * controller/UI thread (on which input events are received).
+   * This does nothing if thread assertions are disabled.
+   */
+  static void AssertOnControllerThread();
+
+  /**
+   * Run the given task on the APZ "controller thread" for this platform. If
+   * this function is called from the controller thread itself then the task is
+   * run immediately without getting queued.
+   */
+  static void RunOnControllerThread(
+      RefPtr<Runnable>&& aTask,
+      uint32_t flags = nsIEventTarget::DISPATCH_NORMAL);
+
+  /**
+   * Returns true if currently on APZ "controller thread".
+   */
+  static bool IsControllerThread();
+
+  /**
+   * Returns true if the controller thread is still alive.
+   */
+  static bool IsControllerThreadAlive();
+
+  /**
+   * Schedules a runnable to run on the controller thread at some time
+   * in the future.
+   */
+  static void DelayedDispatch(already_AddRefed<Runnable> aRunnable,
+                              int aDelayMs);
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_APZThreadUtils_h */
diff --git a/gfx/layers/apz/util/ActiveElementManager.cpp b/gfx/layers/apz/util/ActiveElementManager.cpp
new file mode 100644
index 0000000000..8da36bb2c0
--- /dev/null
+++ b/gfx/layers/apz/util/ActiveElementManager.cpp
@@ -0,0 +1,178 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "ActiveElementManager.h"
+#include "mozilla/EventStateManager.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/StaticPrefs_ui.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/Document.h"
+
+static mozilla::LazyLogModule sApzAemLog("apz.activeelement");
+#define AEM_LOG(...) MOZ_LOG(sApzAemLog, LogLevel::Debug, (__VA_ARGS__))
+
+namespace mozilla {
+namespace layers {
+
+ActiveElementManager::ActiveElementManager()
+    : mCanBePan(false), mCanBePanSet(false), mSetActiveTask(nullptr) {}
+
+ActiveElementManager::~ActiveElementManager() = default;
+
+void ActiveElementManager::SetTargetElement(dom::EventTarget* aTarget) {
+  if (mTarget) {
+    // Multiple fingers on screen (since HandleTouchEnd clears mTarget).
+    AEM_LOG("Multiple fingers on-screen, clearing target element\n");
+    CancelTask();
+    ResetActive();
+    ResetTouchBlockState();
+    return;
+  }
+
+  mTarget = dom::Element::FromEventTargetOrNull(aTarget);
+  AEM_LOG("Setting target element to %p\n", mTarget.get());
+  TriggerElementActivation();
+}
+
+void ActiveElementManager::HandleTouchStart(bool aCanBePan) {
+  AEM_LOG("Touch start, aCanBePan: %d\n", aCanBePan);
+  if (mCanBePanSet) {
+    // Multiple fingers on screen (since HandleTouchEnd clears mCanBePanSet).
+    AEM_LOG("Multiple fingers on-screen, clearing touch block state\n");
+    CancelTask();
+    ResetActive();
+    ResetTouchBlockState();
+    return;
+  }
+
+  mCanBePan = aCanBePan;
+  mCanBePanSet = true;
+  TriggerElementActivation();
+}
+
+void ActiveElementManager::TriggerElementActivation() {
+  // Both HandleTouchStart() and SetTargetElement() call this. They can be
+  // called in either order. One will set mCanBePanSet, and the other, mTarget.
+  // We want to actually trigger the activation once both are set.
+  if (!(mTarget && mCanBePanSet)) {
+    return;
+  }
+
+  // If the touch cannot be a pan, make mTarget :active right away.
+  // Otherwise, wait a bit to see if the user will pan or not.
+  if (!mCanBePan) {
+    SetActive(mTarget);
+  } else {
+    CancelTask();  // this is only needed because of bug 1169802. Fixing that
+                   // bug properly should make this unnecessary.
+    MOZ_ASSERT(mSetActiveTask == nullptr);
+
+    RefPtr<CancelableRunnable> task =
+        NewCancelableRunnableMethod<nsCOMPtr<dom::Element>>(
+            "layers::ActiveElementManager::SetActiveTask", this,
+            &ActiveElementManager::SetActiveTask, mTarget);
+    mSetActiveTask = task;
+    NS_GetCurrentThread()->DelayedDispatch(
+        task.forget(), StaticPrefs::ui_touch_activation_delay_ms());
+    AEM_LOG("Scheduling mSetActiveTask %p\n", mSetActiveTask.get());
+  }
+}
+
+void ActiveElementManager::ClearActivation() {
+  AEM_LOG("Clearing element activation\n");
+  CancelTask();
+  ResetActive();
+}
+
+void ActiveElementManager::HandleTouchEndEvent(bool aWasClick) {
+  AEM_LOG("Touch end event, aWasClick: %d\n", aWasClick);
+
+  // If the touch was a click, make mTarget :active right away.
+  // nsEventStateManager will reset the active element when processing
+  // the mouse-down event generated by the click.
+  CancelTask();
+  if (aWasClick) {
+    // Scrollbar thumbs use a different mechanism for their active
+    // highlight (the "active" attribute), so don't set the active state
+    // on them because nothing will clear it.
+    if (!(mTarget && mTarget->IsXULElement(nsGkAtoms::thumb))) {
+      SetActive(mTarget);
+    }
+  } else {
+    // We might reach here if mCanBePan was false on touch-start and
+    // so we set the element active right away. Now it turns out the
+    // action was not a click so we need to reset the active element.
+    ResetActive();
+  }
+
+  ResetTouchBlockState();
+}
+
+void ActiveElementManager::HandleTouchEnd() {
+  AEM_LOG("Touch end, clearing pan state\n");
+  mCanBePanSet = false;
+}
+
+static nsPresContext* GetPresContextFor(nsIContent* aContent) {
+  if (!aContent) {
+    return nullptr;
+  }
+  PresShell* presShell = aContent->OwnerDoc()->GetPresShell();
+  if (!presShell) {
+    return nullptr;
+  }
+  return presShell->GetPresContext();
+}
+
+void ActiveElementManager::SetActive(dom::Element* aTarget) {
+  AEM_LOG("Setting active %p\n", aTarget);
+
+  if (nsPresContext* pc = GetPresContextFor(aTarget)) {
+    pc->EventStateManager()->SetContentState(aTarget,
+                                             dom::ElementState::ACTIVE);
+  }
+}
+
+void ActiveElementManager::ResetActive() {
+  AEM_LOG("Resetting active from %p\n", mTarget.get());
+
+  // Clear the :active flag from mTarget by setting it on the document root.
+  if (mTarget) {
+    dom::Element* root = mTarget->OwnerDoc()->GetDocumentElement();
+    if (root) {
+      AEM_LOG("Found root %p, making active\n", root);
+      SetActive(root);
+    }
+  }
+}
+
+void ActiveElementManager::ResetTouchBlockState() {
+  mTarget = nullptr;
+  mCanBePanSet = false;
+}
+
+void ActiveElementManager::SetActiveTask(
+    const nsCOMPtr<dom::Element>& aTarget) {
+  AEM_LOG("mSetActiveTask %p running\n", mSetActiveTask.get());
+
+  // This gets called from mSetActiveTask's Run() method. The message loop
+  // deletes the task right after running it, so we need to null out
+  // mSetActiveTask to make sure we're not left with a dangling pointer.
+  mSetActiveTask = nullptr;
+  SetActive(aTarget);
+}
+
+void ActiveElementManager::CancelTask() {
+  AEM_LOG("Cancelling task %p\n", mSetActiveTask.get());
+
+  if (mSetActiveTask) {
+    mSetActiveTask->Cancel();
+    mSetActiveTask = nullptr;
+  }
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/ActiveElementManager.h b/gfx/layers/apz/util/ActiveElementManager.h
new file mode 100644
index 0000000000..b783659962
--- /dev/null
+++ b/gfx/layers/apz/util/ActiveElementManager.h
@@ -0,0 +1,97 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_ActiveElementManager_h
+#define mozilla_layers_ActiveElementManager_h
+
+#include "nsCOMPtr.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla {
+
+class CancelableRunnable;
+
+namespace dom {
+class Element;
+class EventTarget;
+}  // namespace dom
+
+namespace layers {
+
+/**
+ * Manages setting and clearing the ':active' CSS pseudostate in the presence
+ * of touch input.
+ */
+class ActiveElementManager final {
+  ~ActiveElementManager();
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(ActiveElementManager)
+
+  ActiveElementManager();
+
+  /**
+   * Specify the target of a touch. Typically this should be called right
+   * after HandleTouchStart(), but in cases where the APZ needs to wait for
+   * a content response the HandleTouchStart() may be delayed, in which case
+   * this function can be called first.
+   * |aTarget| may be nullptr.
+   */
+  void SetTargetElement(dom::EventTarget* aTarget);
+  /**
+   * Handle a touch-start state notification from APZ. This notification
+   * may be delayed until after touch listeners have responded to the APZ.
+   * @param aCanBePan whether the touch can be a pan
+   */
+  void HandleTouchStart(bool aCanBePan);
+  /**
+   * Clear the active element.
+   */
+  void ClearActivation();
+  /**
+   * Handle a touch-end or touch-cancel event.
+   * @param aWasClick whether the touch was a click
+   */
+  void HandleTouchEndEvent(bool aWasClick);
+  /**
+   * Handle a touch-end state notification from APZ. This notification may be
+   * delayed until after touch listeners have responded to the APZ.
+   */
+  void HandleTouchEnd();
+
+ private:
+  /**
+   * The target of the first touch point in the current touch block.
+   */
+  nsCOMPtr<dom::Element> mTarget;
+  /**
+   * Whether the current touch block can be a pan. Set in HandleTouchStart().
+   */
+  bool mCanBePan;
+  /**
+   * Whether mCanBePan has been set for the current touch block.
+   * We need to keep track of this to allow HandleTouchStart() and
+   * SetTargetElement() to be called in either order.
+   */
+  bool mCanBePanSet;
+  /**
+   * A task for calling SetActive() after a timeout.
+   */
+  RefPtr<CancelableRunnable> mSetActiveTask;
+
+  // Helpers
+  void TriggerElementActivation();
+  void SetActive(dom::Element* aTarget);
+  void ResetActive();
+  void ResetTouchBlockState();
+  void SetActiveTask(const nsCOMPtr<dom::Element>& aTarget);
+  void CancelTask();
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_ActiveElementManager_h */
diff --git a/gfx/layers/apz/util/CheckerboardReportService.cpp b/gfx/layers/apz/util/CheckerboardReportService.cpp
new file mode 100644
index 0000000000..b6ae712b3f
--- /dev/null
+++ b/gfx/layers/apz/util/CheckerboardReportService.cpp
@@ -0,0 +1,217 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "CheckerboardReportService.h"
+
+#include "jsapi.h"                    // for JS_Now
+#include "MainThreadUtils.h"          // for NS_IsMainThread
+#include "mozilla/Assertions.h"       // for MOZ_ASSERT
+#include "mozilla/ClearOnShutdown.h"  // for ClearOnShutdown
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_apz.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/CheckerboardReportServiceBinding.h"  // for dom::CheckerboardReports
+#include "mozilla/gfx/GPUParent.h"
+#include "mozilla/gfx/GPUProcessManager.h"
+#include "nsContentUtils.h"  // for nsContentUtils
+#include "nsIObserverService.h"
+#include "nsXULAppAPI.h"
+
+namespace mozilla {
+namespace layers {
+
+/*static*/
+StaticRefPtr<CheckerboardEventStorage> CheckerboardEventStorage::sInstance;
+
+/*static*/
+already_AddRefed<CheckerboardEventStorage>
+CheckerboardEventStorage::GetInstance() {
+  // The instance in the parent process does all the work, so if this is getting
+  // called in the child process something is likely wrong.
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  MOZ_ASSERT(NS_IsMainThread());
+  if (!sInstance) {
+    sInstance = new CheckerboardEventStorage();
+    ClearOnShutdown(&sInstance);
+  }
+  RefPtr<CheckerboardEventStorage> instance = sInstance.get();
+  return instance.forget();
+}
+
+void CheckerboardEventStorage::Report(uint32_t aSeverity,
+                                      const std::string& aLog) {
+  if (!NS_IsMainThread()) {
+    RefPtr<Runnable> task = NS_NewRunnableFunction(
+        "layers::CheckerboardEventStorage::Report",
+        [aSeverity, aLog]() -> void {
+          CheckerboardEventStorage::Report(aSeverity, aLog);
+        });
+    NS_DispatchToMainThread(task.forget());
+    return;
+  }
+
+  if (XRE_IsGPUProcess()) {
+    if (gfx::GPUParent* gpu = gfx::GPUParent::GetSingleton()) {
+      nsCString log(aLog.c_str());
+      Unused << gpu->SendReportCheckerboard(aSeverity, log);
+    }
+    return;
+  }
+
+  RefPtr<CheckerboardEventStorage> storage = GetInstance();
+  storage->ReportCheckerboard(aSeverity, aLog);
+}
+
+void CheckerboardEventStorage::ReportCheckerboard(uint32_t aSeverity,
+                                                  const std::string& aLog) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (aSeverity == 0) {
+    // This code assumes all checkerboard reports have a nonzero severity.
+    return;
+  }
+
+  CheckerboardReport severe(aSeverity, JS_Now(), aLog);
+  CheckerboardReport recent;
+
+  // First look in the "severe" reports to see if the new one belongs in that
+  // list.
+  for (int i = 0; i < SEVERITY_MAX_INDEX; i++) {
+    if (mCheckerboardReports[i].mSeverity >= severe.mSeverity) {
+      continue;
+    }
+    // The new one deserves to be in the "severe" list. Take the one getting
+    // bumped off the list, and put it in |recent| for possible insertion into
+    // the recents list.
+    recent = mCheckerboardReports[SEVERITY_MAX_INDEX - 1];
+
+    // Shuffle the severe list down, insert the new one.
+    for (int j = SEVERITY_MAX_INDEX - 1; j > i; j--) {
+      mCheckerboardReports[j] = mCheckerboardReports[j - 1];
+    }
+    mCheckerboardReports[i] = severe;
+    severe.mSeverity = 0;  // mark |severe| as inserted
+    break;
+  }
+
+  // If |severe.mSeverity| is nonzero, the incoming report didn't get inserted
+  // into the severe list; put it into |recent| for insertion into the recent
+  // list.
+  if (severe.mSeverity) {
+    MOZ_ASSERT(recent.mSeverity == 0, "recent should be empty here");
+    recent = severe;
+  }  // else |recent| may hold a report that got knocked out of the severe list.
+
+  if (recent.mSeverity == 0) {
+    // Nothing to be inserted into the recent list.
+    return;
+  }
+
+  // If it wasn't in the "severe" list, add it to the "recent" list.
+  for (int i = SEVERITY_MAX_INDEX; i < RECENT_MAX_INDEX; i++) {
+    if (mCheckerboardReports[i].mTimestamp >= recent.mTimestamp) {
+      continue;
+    }
+    // |recent| needs to be inserted at |i|. Shuffle the remaining ones down
+    // and insert it.
+    for (int j = RECENT_MAX_INDEX - 1; j > i; j--) {
+      mCheckerboardReports[j] = mCheckerboardReports[j - 1];
+    }
+    mCheckerboardReports[i] = recent;
+    break;
+  }
+}
+
+void CheckerboardEventStorage::GetReports(
+    nsTArray<dom::CheckerboardReport>& aOutReports) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  for (int i = 0; i < RECENT_MAX_INDEX; i++) {
+    CheckerboardReport& r = mCheckerboardReports[i];
+    if (r.mSeverity == 0) {
+      continue;
+    }
+    dom::CheckerboardReport report;
+    report.mSeverity.Construct() = r.mSeverity;
+    report.mTimestamp.Construct() = r.mTimestamp / 1000;  // micros to millis
+    report.mLog.Construct() =
+        NS_ConvertUTF8toUTF16(r.mLog.c_str(), r.mLog.size());
+    report.mReason.Construct() = (i < SEVERITY_MAX_INDEX)
+                                     ? dom::CheckerboardReason::Severe
+                                     : dom::CheckerboardReason::Recent;
+    aOutReports.AppendElement(report);
+  }
+}
+
+}  // namespace layers
+
+namespace dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(CheckerboardReportService, mParent)
+
+/*static*/
+bool CheckerboardReportService::IsEnabled(JSContext* aCtx, JSObject* aGlobal) {
+  // Only allow this in the parent process
+  if (!XRE_IsParentProcess()) {
+    return false;
+  }
+  // Allow privileged code or about:checkerboard (unprivileged) to access this.
+  return nsContentUtils::IsSystemCaller(aCtx) ||
+         nsContentUtils::IsSpecificAboutPage(aGlobal, "about:checkerboard");
+}
+
+/*static*/
+already_AddRefed<CheckerboardReportService>
+CheckerboardReportService::Constructor(const dom::GlobalObject& aGlobal) {
+  RefPtr<CheckerboardReportService> ces =
+      new CheckerboardReportService(aGlobal.GetAsSupports());
+  return ces.forget();
+}
+
+CheckerboardReportService::CheckerboardReportService(nsISupports* aParent)
+    : mParent(aParent) {}
+
+JSObject* CheckerboardReportService::WrapObject(
+    JSContext* aCtx, JS::Handle<JSObject*> aGivenProto) {
+  return CheckerboardReportService_Binding::Wrap(aCtx, this, aGivenProto);
+}
+
+nsISupports* CheckerboardReportService::GetParentObject() { return mParent; }
+
+void CheckerboardReportService::GetReports(
+    nsTArray<dom::CheckerboardReport>& aOutReports) {
+  RefPtr<mozilla::layers::CheckerboardEventStorage> instance =
+      mozilla::layers::CheckerboardEventStorage::GetInstance();
+  MOZ_ASSERT(instance);
+  instance->GetReports(aOutReports);
+}
+
+bool CheckerboardReportService::IsRecordingEnabled() const {
+  return StaticPrefs::apz_record_checkerboarding();
+}
+
+void CheckerboardReportService::SetRecordingEnabled(bool aEnabled) {
+  Preferences::SetBool("apz.record_checkerboarding", aEnabled);
+}
+
+void CheckerboardReportService::FlushActiveReports() {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  gfx::GPUProcessManager* gpu = gfx::GPUProcessManager::Get();
+  if (gpu && gpu->NotifyGpuObservers("APZ:FlushActiveCheckerboard")) {
+    return;
+  }
+
+  nsCOMPtr<nsIObserverService> obsSvc = mozilla::services::GetObserverService();
+  MOZ_ASSERT(obsSvc);
+  if (obsSvc) {
+    obsSvc->NotifyObservers(nullptr, "APZ:FlushActiveCheckerboard", nullptr);
+  }
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/CheckerboardReportService.h b/gfx/layers/apz/util/CheckerboardReportService.h
new file mode 100644
index 0000000000..d9b37509c5
--- /dev/null
+++ b/gfx/layers/apz/util/CheckerboardReportService.h
@@ -0,0 +1,138 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_dom_CheckerboardReportService_h
+#define mozilla_dom_CheckerboardReportService_h
+
+#include <string>
+
+#include "js/TypeDecls.h"            // for JSContext, JSObject
+#include "mozilla/StaticPtr.h"       // for StaticRefPtr
+#include "nsCOMPtr.h"                // for nsCOMPtr
+#include "nsISupports.h"             // for NS_INLINE_DECL_REFCOUNTING
+#include "nsTArrayForwardDeclare.h"  // for nsTArray
+#include "nsWrapperCache.h"          // for nsWrapperCache
+
+namespace mozilla {
+
+namespace dom {
+struct CheckerboardReport;
+}
+
+namespace layers {
+
+// CheckerboardEventStorage is a singleton that stores info on checkerboard
+// events, so that they can be accessed from about:checkerboard and visualized.
+// Note that this class is NOT threadsafe, and all methods must be called on
+// the main thread.
+class CheckerboardEventStorage {
+  NS_INLINE_DECL_REFCOUNTING(CheckerboardEventStorage)
+
+ public:
+  /**
+   * Get the singleton instance.
+   */
+  static already_AddRefed<CheckerboardEventStorage> GetInstance();
+
+  /**
+   * Get the stored checkerboard reports.
+   */
+  void GetReports(nsTArray<dom::CheckerboardReport>& aOutReports);
+
+  /**
+   * Save a checkerboard event log, optionally dropping older ones that were
+   * less severe or less recent. Zero-severity reports may be ignored entirely.
+   */
+  static void Report(uint32_t aSeverity, const std::string& aLog);
+
+ private:
+  /* Stuff for refcounted singleton */
+  CheckerboardEventStorage() = default;
+  virtual ~CheckerboardEventStorage() = default;
+
+  static StaticRefPtr<CheckerboardEventStorage> sInstance;
+
+  void ReportCheckerboard(uint32_t aSeverity, const std::string& aLog);
+
+ private:
+  /**
+   * Struct that this class uses internally to store a checkerboard report.
+   */
+  struct CheckerboardReport {
+    uint32_t mSeverity;  // if 0, this report is empty
+    int64_t mTimestamp;  // microseconds since epoch, as from JS_Now()
+    std::string mLog;
+
+    CheckerboardReport() : mSeverity(0), mTimestamp(0) {}
+
+    CheckerboardReport(uint32_t aSeverity, int64_t aTimestamp,
+                       const std::string& aLog)
+        : mSeverity(aSeverity), mTimestamp(aTimestamp), mLog(aLog) {}
+  };
+
+  // The first 5 (indices 0-4) are the most severe ones in decreasing order
+  // of severity; the next 5 (indices 5-9) are the most recent ones that are
+  // not already in the "severe" list.
+  static const int SEVERITY_MAX_INDEX = 5;
+  static const int RECENT_MAX_INDEX = 10;
+  CheckerboardReport mCheckerboardReports[RECENT_MAX_INDEX];
+};
+
+}  // namespace layers
+
+namespace dom {
+
+class GlobalObject;
+
+/**
+ * CheckerboardReportService is a wrapper object that allows access to the
+ * stuff in CheckerboardEventStorage (above). We need this wrapper for proper
+ * garbage/cycle collection, since this can be accessed from JS.
+ */
+class CheckerboardReportService : public nsWrapperCache {
+ public:
+  /**
+   * Check if the given page is allowed to access this object via the WebIDL
+   * bindings. It only returns true if the page is about:checkerboard.
+   */
+  static bool IsEnabled(JSContext* aCtx, JSObject* aGlobal);
+
+  /*
+   * Other standard WebIDL binding glue.
+   */
+
+  static already_AddRefed<CheckerboardReportService> Constructor(
+      const dom::GlobalObject& aGlobal);
+
+  explicit CheckerboardReportService(nsISupports* aSupports);
+
+  JSObject* WrapObject(JSContext* aCtx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  nsISupports* GetParentObject();
+
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(CheckerboardReportService)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(CheckerboardReportService)
+
+ public:
+  /*
+   * The methods exposed via the webidl.
+   */
+  void GetReports(nsTArray<dom::CheckerboardReport>& aOutReports);
+  bool IsRecordingEnabled() const;
+  void SetRecordingEnabled(bool aEnabled);
+  void FlushActiveReports();
+
+ private:
+  virtual ~CheckerboardReportService() = default;
+
+  nsCOMPtr<nsISupports> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* mozilla_layers_CheckerboardReportService_h */
diff --git a/gfx/layers/apz/util/ChromeProcessController.cpp b/gfx/layers/apz/util/ChromeProcessController.cpp
new file mode 100644
index 0000000000..d16466ad7a
--- /dev/null
+++ b/gfx/layers/apz/util/ChromeProcessController.cpp
@@ -0,0 +1,356 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "ChromeProcessController.h"
+
+#include "MainThreadUtils.h"  // for NS_IsMainThread()
+#include "base/task.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/layers/CompositorBridgeParent.h"
+#include "mozilla/layers/APZCCallbackHelper.h"
+#include "mozilla/layers/APZEventState.h"
+#include "mozilla/layers/APZThreadUtils.h"
+#include "mozilla/layers/IAPZCTreeManager.h"
+#include "mozilla/layers/InputAPZContext.h"
+#include "mozilla/layers/DoubleTapToZoom.h"
+#include "mozilla/layers/RepaintRequest.h"
+#include "mozilla/dom/Document.h"
+#include "nsIInterfaceRequestorUtils.h"
+#include "nsLayoutUtils.h"
+#include "nsView.h"
+
+static mozilla::LazyLogModule sApzChromeLog("apz.cc.chrome");
+
+using namespace mozilla;
+using namespace mozilla::layers;
+using namespace mozilla::widget;
+
+ChromeProcessController::ChromeProcessController(
+    nsIWidget* aWidget, APZEventState* aAPZEventState,
+    IAPZCTreeManager* aAPZCTreeManager)
+    : mWidget(aWidget),
+      mAPZEventState(aAPZEventState),
+      mAPZCTreeManager(aAPZCTreeManager),
+      mUIThread(NS_GetCurrentThread()) {
+  // Otherwise we're initializing mUIThread incorrectly.
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aAPZEventState);
+  MOZ_ASSERT(aAPZCTreeManager);
+
+  mUIThread->Dispatch(
+      NewRunnableMethod("layers::ChromeProcessController::InitializeRoot", this,
+                        &ChromeProcessController::InitializeRoot));
+}
+
+ChromeProcessController::~ChromeProcessController() = default;
+
+void ChromeProcessController::InitializeRoot() {
+  APZCCallbackHelper::InitializeRootDisplayport(GetPresShell());
+}
+
+void ChromeProcessController::NotifyLayerTransforms(
+    nsTArray<MatrixMessage>&& aTransforms) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(
+        NewRunnableMethod<StoreCopyPassByRRef<nsTArray<MatrixMessage>>>(
+            "layers::ChromeProcessController::NotifyLayerTransforms", this,
+            &ChromeProcessController::NotifyLayerTransforms,
+            std::move(aTransforms)));
+    return;
+  }
+
+  APZCCallbackHelper::NotifyLayerTransforms(aTransforms);
+}
+
+void ChromeProcessController::RequestContentRepaint(
+    const RepaintRequest& aRequest) {
+  MOZ_ASSERT(IsRepaintThread());
+
+  if (aRequest.IsRootContent()) {
+    APZCCallbackHelper::UpdateRootFrame(aRequest);
+  } else {
+    APZCCallbackHelper::UpdateSubFrame(aRequest);
+  }
+}
+
+bool ChromeProcessController::IsRepaintThread() { return NS_IsMainThread(); }
+
+void ChromeProcessController::DispatchToRepaintThread(
+    already_AddRefed<Runnable> aTask) {
+  NS_DispatchToMainThread(std::move(aTask));
+}
+
+void ChromeProcessController::Destroy() {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(
+        NewRunnableMethod("layers::ChromeProcessController::Destroy", this,
+                          &ChromeProcessController::Destroy));
+    return;
+  }
+
+  MOZ_ASSERT(mUIThread->IsOnCurrentThread());
+  mWidget = nullptr;
+  mAPZEventState = nullptr;
+}
+
+PresShell* ChromeProcessController::GetPresShell() const {
+  if (!mWidget) {
+    return nullptr;
+  }
+  if (nsView* view = nsView::GetViewFor(mWidget)) {
+    return view->GetPresShell();
+  }
+  return nullptr;
+}
+
+dom::Document* ChromeProcessController::GetRootDocument() const {
+  if (PresShell* presShell = GetPresShell()) {
+    return presShell->GetDocument();
+  }
+  return nullptr;
+}
+
+dom::Document* ChromeProcessController::GetRootContentDocument(
+    const ScrollableLayerGuid::ViewID& aScrollId) const {
+  nsIContent* content = nsLayoutUtils::FindContentFor(aScrollId);
+  if (!content) {
+    return nullptr;
+  }
+  if (PresShell* presShell =
+          APZCCallbackHelper::GetRootContentDocumentPresShellForContent(
+              content)) {
+    return presShell->GetDocument();
+  }
+  return nullptr;
+}
+
+void ChromeProcessController::HandleDoubleTap(
+    const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
+    const ScrollableLayerGuid& aGuid) {
+  MOZ_ASSERT(mUIThread->IsOnCurrentThread());
+
+  RefPtr<dom::Document> document = GetRootContentDocument(aGuid.mScrollId);
+  if (!document.get()) {
+    return;
+  }
+
+  ZoomTarget zoomTarget = CalculateRectToZoomTo(document, aPoint);
+
+  uint32_t presShellId;
+  ScrollableLayerGuid::ViewID viewId;
+  if (APZCCallbackHelper::GetOrCreateScrollIdentifiers(
+          document->GetDocumentElement(), &presShellId, &viewId)) {
+    mAPZCTreeManager->ZoomToRect(
+        ScrollableLayerGuid(aGuid.mLayersId, presShellId, viewId), zoomTarget,
+        ZoomToRectBehavior::DEFAULT_BEHAVIOR);
+  }
+}
+
+void ChromeProcessController::HandleTap(
+    TapType aType, const mozilla::LayoutDevicePoint& aPoint,
+    Modifiers aModifiers, const ScrollableLayerGuid& aGuid,
+    uint64_t aInputBlockId) {
+  MOZ_LOG(sApzChromeLog, LogLevel::Debug,
+          ("HandleTap called with %d\n", (int)aType));
+  if (!mUIThread->IsOnCurrentThread()) {
+    MOZ_LOG(sApzChromeLog, LogLevel::Debug, ("HandleTap redispatching\n"));
+    mUIThread->Dispatch(
+        NewRunnableMethod<TapType, mozilla::LayoutDevicePoint, Modifiers,
+                          ScrollableLayerGuid, uint64_t>(
+            "layers::ChromeProcessController::HandleTap", this,
+            &ChromeProcessController::HandleTap, aType, aPoint, aModifiers,
+            aGuid, aInputBlockId));
+    return;
+  }
+
+  if (!mAPZEventState) {
+    return;
+  }
+
+  RefPtr<PresShell> presShell = GetPresShell();
+  if (!presShell) {
+    return;
+  }
+  if (!presShell->GetPresContext()) {
+    return;
+  }
+  CSSToLayoutDeviceScale scale(
+      presShell->GetPresContext()->CSSToDevPixelScale());
+
+  CSSPoint point = aPoint / scale;
+
+  // Stash the guid in InputAPZContext so that when the visual-to-layout
+  // transform is applied to the event's coordinates, we use the right transform
+  // based on the scroll frame being targeted.
+  // The other values don't really matter.
+  InputAPZContext context(aGuid, aInputBlockId, nsEventStatus_eSentinel);
+
+  switch (aType) {
+    case TapType::eSingleTap:
+      mAPZEventState->ProcessSingleTap(point, scale, aModifiers, 1,
+                                       aInputBlockId);
+      break;
+    case TapType::eDoubleTap:
+      HandleDoubleTap(point, aModifiers, aGuid);
+      break;
+    case TapType::eSecondTap:
+      mAPZEventState->ProcessSingleTap(point, scale, aModifiers, 2,
+                                       aInputBlockId);
+      break;
+    case TapType::eLongTap: {
+      RefPtr<APZEventState> eventState(mAPZEventState);
+      eventState->ProcessLongTap(presShell, point, scale, aModifiers,
+                                 aInputBlockId);
+      break;
+    }
+    case TapType::eLongTapUp: {
+      RefPtr<APZEventState> eventState(mAPZEventState);
+      eventState->ProcessLongTapUp(presShell, point, scale, aModifiers);
+      break;
+    }
+  }
+}
+
+void ChromeProcessController::NotifyPinchGesture(
+    PinchGestureInput::PinchGestureType aType, const ScrollableLayerGuid& aGuid,
+    const LayoutDevicePoint& aFocusPoint, LayoutDeviceCoord aSpanChange,
+    Modifiers aModifiers) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(
+        NewRunnableMethod<PinchGestureInput::PinchGestureType,
+                          ScrollableLayerGuid, LayoutDevicePoint,
+                          LayoutDeviceCoord, Modifiers>(
+            "layers::ChromeProcessController::NotifyPinchGesture", this,
+            &ChromeProcessController::NotifyPinchGesture, aType, aGuid,
+            aFocusPoint, aSpanChange, aModifiers));
+    return;
+  }
+
+  if (mWidget) {
+    // Dispatch the call to APZCCallbackHelper::NotifyPinchGesture to the main
+    // thread so that it runs asynchronously from the current call. This is
+    // because the call can run arbitrary JS code, which can also spin the event
+    // loop and cause undesirable re-entrancy in APZ.
+    mUIThread->Dispatch(NewRunnableFunction(
+        "layers::ChromeProcessController::NotifyPinchGestureAsync",
+        &APZCCallbackHelper::NotifyPinchGesture, aType, aFocusPoint,
+        aSpanChange, aModifiers, mWidget));
+  }
+}
+
+void ChromeProcessController::NotifyAPZStateChange(
+    const ScrollableLayerGuid& aGuid, APZStateChange aChange, int aArg,
+    Maybe<uint64_t> aInputBlockId) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(NewRunnableMethod<ScrollableLayerGuid, APZStateChange,
+                                          int, Maybe<uint64_t>>(
+        "layers::ChromeProcessController::NotifyAPZStateChange", this,
+        &ChromeProcessController::NotifyAPZStateChange, aGuid, aChange, aArg,
+        aInputBlockId));
+    return;
+  }
+
+  if (!mAPZEventState) {
+    return;
+  }
+
+  mAPZEventState->ProcessAPZStateChange(aGuid.mScrollId, aChange, aArg,
+                                        aInputBlockId);
+}
+
+void ChromeProcessController::NotifyMozMouseScrollEvent(
+    const ScrollableLayerGuid::ViewID& aScrollId, const nsString& aEvent) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(
+        NewRunnableMethod<ScrollableLayerGuid::ViewID, nsString>(
+            "layers::ChromeProcessController::NotifyMozMouseScrollEvent", this,
+            &ChromeProcessController::NotifyMozMouseScrollEvent, aScrollId,
+            aEvent));
+    return;
+  }
+
+  APZCCallbackHelper::NotifyMozMouseScrollEvent(aScrollId, aEvent);
+}
+
+void ChromeProcessController::NotifyFlushComplete() {
+  MOZ_ASSERT(IsRepaintThread());
+
+  APZCCallbackHelper::NotifyFlushComplete(GetPresShell());
+}
+
+void ChromeProcessController::NotifyAsyncScrollbarDragInitiated(
+    uint64_t aDragBlockId, const ScrollableLayerGuid::ViewID& aScrollId,
+    ScrollDirection aDirection) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(NewRunnableMethod<uint64_t, ScrollableLayerGuid::ViewID,
+                                          ScrollDirection>(
+        "layers::ChromeProcessController::NotifyAsyncScrollbarDragInitiated",
+        this, &ChromeProcessController::NotifyAsyncScrollbarDragInitiated,
+        aDragBlockId, aScrollId, aDirection));
+    return;
+  }
+
+  APZCCallbackHelper::NotifyAsyncScrollbarDragInitiated(aDragBlockId, aScrollId,
+                                                        aDirection);
+}
+
+void ChromeProcessController::NotifyAsyncScrollbarDragRejected(
+    const ScrollableLayerGuid::ViewID& aScrollId) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(NewRunnableMethod<ScrollableLayerGuid::ViewID>(
+        "layers::ChromeProcessController::NotifyAsyncScrollbarDragRejected",
+        this, &ChromeProcessController::NotifyAsyncScrollbarDragRejected,
+        aScrollId));
+    return;
+  }
+
+  APZCCallbackHelper::NotifyAsyncScrollbarDragRejected(aScrollId);
+}
+
+void ChromeProcessController::NotifyAsyncAutoscrollRejected(
+    const ScrollableLayerGuid::ViewID& aScrollId) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(NewRunnableMethod<ScrollableLayerGuid::ViewID>(
+        "layers::ChromeProcessController::NotifyAsyncAutoscrollRejected", this,
+        &ChromeProcessController::NotifyAsyncAutoscrollRejected, aScrollId));
+    return;
+  }
+
+  APZCCallbackHelper::NotifyAsyncAutoscrollRejected(aScrollId);
+}
+
+void ChromeProcessController::CancelAutoscroll(
+    const ScrollableLayerGuid& aGuid) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(NewRunnableMethod<ScrollableLayerGuid>(
+        "layers::ChromeProcessController::CancelAutoscroll", this,
+        &ChromeProcessController::CancelAutoscroll, aGuid));
+    return;
+  }
+
+  APZCCallbackHelper::CancelAutoscroll(aGuid.mScrollId);
+}
+
+void ChromeProcessController::NotifyScaleGestureComplete(
+    const ScrollableLayerGuid& aGuid, float aScale) {
+  if (!mUIThread->IsOnCurrentThread()) {
+    mUIThread->Dispatch(NewRunnableMethod<ScrollableLayerGuid, float>(
+        "layers::ChromeProcessController::NotifyScaleGestureComplete", this,
+        &ChromeProcessController::NotifyScaleGestureComplete, aGuid, aScale));
+    return;
+  }
+
+  if (mWidget) {
+    // Dispatch the call to APZCCallbackHelper::NotifyScaleGestureComplete
+    // to the main thread so that it runs asynchronously from the current call.
+    // This is because the call can run arbitrary JS code, which can also spin
+    // the event loop and cause undesirable re-entrancy in APZ.
+    mUIThread->Dispatch(NewRunnableFunction(
+        "layers::ChromeProcessController::NotifyScaleGestureComplete",
+        &APZCCallbackHelper::NotifyScaleGestureComplete, mWidget, aScale));
+  }
+}
diff --git a/gfx/layers/apz/util/ChromeProcessController.h b/gfx/layers/apz/util/ChromeProcessController.h
new file mode 100644
index 0000000000..7328d62adb
--- /dev/null
+++ b/gfx/layers/apz/util/ChromeProcessController.h
@@ -0,0 +1,102 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_ChromeProcessController_h
+#define mozilla_layers_ChromeProcessController_h
+
+#include "mozilla/layers/GeckoContentController.h"
+#include "nsCOMPtr.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/layers/MatrixMessage.h"
+
+class nsIDOMWindowUtils;
+class nsISerialEventTarget;
+class nsIWidget;
+
+namespace mozilla {
+class PresShell;
+namespace dom {
+class Document;
+}
+
+namespace layers {
+
+class IAPZCTreeManager;
+class APZEventState;
+
+/**
+ * ChromeProcessController is a GeckoContentController attached to the root of
+ * a compositor's layer tree. It's used directly by APZ by default, and remoted
+ * using PAPZ if there is a gpu process.
+ *
+ * If ChromeProcessController needs to implement a new method on
+ * GeckoContentController PAPZ, APZChild, and RemoteContentController must be
+ * updated to handle it.
+ */
+class ChromeProcessController : public mozilla::layers::GeckoContentController {
+ protected:
+  typedef mozilla::layers::FrameMetrics FrameMetrics;
+  typedef mozilla::layers::ScrollableLayerGuid ScrollableLayerGuid;
+
+ public:
+  explicit ChromeProcessController(nsIWidget* aWidget,
+                                   APZEventState* aAPZEventState,
+                                   IAPZCTreeManager* aAPZCTreeManager);
+  virtual ~ChromeProcessController();
+  void Destroy() override;
+
+  // GeckoContentController interface
+  void NotifyLayerTransforms(nsTArray<MatrixMessage>&& aTransforms) override;
+  void RequestContentRepaint(const RepaintRequest& aRequest) override;
+  bool IsRepaintThread() override;
+  void DispatchToRepaintThread(already_AddRefed<Runnable> aTask) override;
+  MOZ_CAN_RUN_SCRIPT
+  void HandleTap(TapType aType, const mozilla::LayoutDevicePoint& aPoint,
+                 Modifiers aModifiers, const ScrollableLayerGuid& aGuid,
+                 uint64_t aInputBlockId) override;
+  void NotifyPinchGesture(PinchGestureInput::PinchGestureType aType,
+                          const ScrollableLayerGuid& aGuid,
+                          const LayoutDevicePoint& aFocusPoint,
+                          LayoutDeviceCoord aSpanChange,
+                          Modifiers aModifiers) override;
+  void NotifyAPZStateChange(const ScrollableLayerGuid& aGuid,
+                            APZStateChange aChange, int aArg,
+                            Maybe<uint64_t> aInputBlockId) override;
+  void NotifyMozMouseScrollEvent(const ScrollableLayerGuid::ViewID& aScrollId,
+                                 const nsString& aEvent) override;
+  void NotifyFlushComplete() override;
+  void NotifyAsyncScrollbarDragInitiated(
+      uint64_t aDragBlockId, const ScrollableLayerGuid::ViewID& aScrollId,
+      ScrollDirection aDirection) override;
+  void NotifyAsyncScrollbarDragRejected(
+      const ScrollableLayerGuid::ViewID& aScrollId) override;
+  void NotifyAsyncAutoscrollRejected(
+      const ScrollableLayerGuid::ViewID& aScrollId) override;
+  void CancelAutoscroll(const ScrollableLayerGuid& aGuid) override;
+  void NotifyScaleGestureComplete(const ScrollableLayerGuid& aGuid,
+                                  float aScale) override;
+
+  PresShell* GetTopLevelPresShell() const override { return GetPresShell(); }
+
+ private:
+  nsCOMPtr<nsIWidget> mWidget;
+  RefPtr<APZEventState> mAPZEventState;
+  RefPtr<IAPZCTreeManager> mAPZCTreeManager;
+  nsCOMPtr<nsISerialEventTarget> mUIThread;
+
+  void InitializeRoot();
+  PresShell* GetPresShell() const;
+  dom::Document* GetRootDocument() const;
+  dom::Document* GetRootContentDocument(
+      const ScrollableLayerGuid::ViewID& aScrollId) const;
+  void HandleDoubleTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
+                       const ScrollableLayerGuid& aGuid);
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_ChromeProcessController_h */
diff --git a/gfx/layers/apz/util/ContentProcessController.cpp b/gfx/layers/apz/util/ContentProcessController.cpp
new file mode 100644
index 0000000000..332d0523fe
--- /dev/null
+++ b/gfx/layers/apz/util/ContentProcessController.cpp
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "ContentProcessController.h"
+
+#include "mozilla/PresShell.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/layers/APZCCallbackHelper.h"
+#include "mozilla/layers/APZChild.h"
+#include "nsIContentInlines.h"
+
+#include "InputData.h"  // for InputData
+
+namespace mozilla {
+namespace layers {
+
+ContentProcessController::ContentProcessController(
+    const RefPtr<dom::BrowserChild>& aBrowser)
+    : mBrowser(aBrowser) {
+  MOZ_ASSERT(mBrowser);
+}
+
+void ContentProcessController::NotifyLayerTransforms(
+    nsTArray<MatrixMessage>&& aTransforms) {
+  // This should never get called
+  MOZ_ASSERT(false);
+}
+
+void ContentProcessController::RequestContentRepaint(
+    const RepaintRequest& aRequest) {
+  if (mBrowser) {
+    mBrowser->UpdateFrame(aRequest);
+  }
+}
+
+void ContentProcessController::HandleTap(TapType aType,
+                                         const LayoutDevicePoint& aPoint,
+                                         Modifiers aModifiers,
+                                         const ScrollableLayerGuid& aGuid,
+                                         uint64_t aInputBlockId) {
+  // This should never get called
+  MOZ_ASSERT(false);
+}
+
+void ContentProcessController::NotifyPinchGesture(
+    PinchGestureInput::PinchGestureType aType, const ScrollableLayerGuid& aGuid,
+    const LayoutDevicePoint& aFocusPoint, LayoutDeviceCoord aSpanChange,
+    Modifiers aModifiers) {
+  // This should never get called
+  MOZ_ASSERT_UNREACHABLE("Unexpected message to content process");
+}
+
+void ContentProcessController::NotifyAPZStateChange(
+    const ScrollableLayerGuid& aGuid, APZStateChange aChange, int aArg,
+    Maybe<uint64_t> aInputBlockId) {
+  if (mBrowser) {
+    mBrowser->NotifyAPZStateChange(aGuid.mScrollId, aChange, aArg,
+                                   aInputBlockId);
+  }
+}
+
+void ContentProcessController::NotifyMozMouseScrollEvent(
+    const ScrollableLayerGuid::ViewID& aScrollId, const nsString& aEvent) {
+  if (mBrowser) {
+    APZCCallbackHelper::NotifyMozMouseScrollEvent(aScrollId, aEvent);
+  }
+}
+
+void ContentProcessController::NotifyFlushComplete() {
+  if (mBrowser) {
+    RefPtr<PresShell> presShell = mBrowser->GetTopLevelPresShell();
+    APZCCallbackHelper::NotifyFlushComplete(presShell);
+  }
+}
+
+void ContentProcessController::NotifyAsyncScrollbarDragInitiated(
+    uint64_t aDragBlockId, const ScrollableLayerGuid::ViewID& aScrollId,
+    ScrollDirection aDirection) {
+  APZCCallbackHelper::NotifyAsyncScrollbarDragInitiated(aDragBlockId, aScrollId,
+                                                        aDirection);
+}
+
+void ContentProcessController::NotifyAsyncScrollbarDragRejected(
+    const ScrollableLayerGuid::ViewID& aScrollId) {
+  APZCCallbackHelper::NotifyAsyncScrollbarDragRejected(aScrollId);
+}
+
+void ContentProcessController::NotifyAsyncAutoscrollRejected(
+    const ScrollableLayerGuid::ViewID& aScrollId) {
+  APZCCallbackHelper::NotifyAsyncAutoscrollRejected(aScrollId);
+}
+
+void ContentProcessController::CancelAutoscroll(
+    const ScrollableLayerGuid& aGuid) {
+  // This should never get called
+  MOZ_ASSERT_UNREACHABLE("Unexpected message to content process");
+}
+
+void ContentProcessController::NotifyScaleGestureComplete(
+    const ScrollableLayerGuid& aGuid, float aScale) {
+  // This should never get called
+  MOZ_ASSERT_UNREACHABLE("Unexpected message to content process");
+}
+
+bool ContentProcessController::IsRepaintThread() { return NS_IsMainThread(); }
+
+void ContentProcessController::DispatchToRepaintThread(
+    already_AddRefed<Runnable> aTask) {
+  NS_DispatchToMainThread(std::move(aTask));
+}
+
+PresShell* ContentProcessController::GetTopLevelPresShell() const {
+  if (!mBrowser) {
+    return nullptr;
+  }
+  return mBrowser->GetTopLevelPresShell();
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/ContentProcessController.h b/gfx/layers/apz/util/ContentProcessController.h
new file mode 100644
index 0000000000..02d32df72e
--- /dev/null
+++ b/gfx/layers/apz/util/ContentProcessController.h
@@ -0,0 +1,93 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_ContentProcessController_h
+#define mozilla_layers_ContentProcessController_h
+
+#include "mozilla/layers/GeckoContentController.h"
+
+class nsIObserver;
+
+namespace mozilla {
+
+namespace dom {
+class BrowserChild;
+}  // namespace dom
+
+namespace layers {
+
+class APZChild;
+
+/**
+ * ContentProcessController is a GeckoContentController for a BrowserChild, and
+ * is always remoted using PAPZ/APZChild.
+ *
+ * ContentProcessController is created in ContentChild when a layer tree id has
+ * been allocated for a PBrowser that lives in that content process, and is
+ * destroyed when the Destroy message is received, or when the tab dies.
+ *
+ * If ContentProcessController needs to implement a new method on
+ * GeckoContentController PAPZ, APZChild, and RemoteContentController must be
+ * updated to handle it.
+ */
+class ContentProcessController final : public GeckoContentController {
+ public:
+  explicit ContentProcessController(const RefPtr<dom::BrowserChild>& aBrowser);
+
+  // GeckoContentController
+
+  void NotifyLayerTransforms(nsTArray<MatrixMessage>&& aTransforms) override;
+
+  void RequestContentRepaint(const RepaintRequest& aRequest) override;
+
+  void HandleTap(TapType aType, const LayoutDevicePoint& aPoint,
+                 Modifiers aModifiers, const ScrollableLayerGuid& aGuid,
+                 uint64_t aInputBlockId) override;
+
+  void NotifyPinchGesture(PinchGestureInput::PinchGestureType aType,
+                          const ScrollableLayerGuid& aGuid,
+                          const LayoutDevicePoint& aFocusPoint,
+                          LayoutDeviceCoord aSpanChange,
+                          Modifiers aModifiers) override;
+
+  void NotifyAPZStateChange(const ScrollableLayerGuid& aGuid,
+                            APZStateChange aChange, int aArg,
+                            Maybe<uint64_t> aInputBlockId) override;
+
+  void NotifyMozMouseScrollEvent(const ScrollableLayerGuid::ViewID& aScrollId,
+                                 const nsString& aEvent) override;
+
+  void NotifyFlushComplete() override;
+
+  void NotifyAsyncScrollbarDragInitiated(
+      uint64_t aDragBlockId, const ScrollableLayerGuid::ViewID& aScrollId,
+      ScrollDirection aDirection) override;
+  void NotifyAsyncScrollbarDragRejected(
+      const ScrollableLayerGuid::ViewID& aScrollId) override;
+
+  void NotifyAsyncAutoscrollRejected(
+      const ScrollableLayerGuid::ViewID& aScrollId) override;
+
+  void CancelAutoscroll(const ScrollableLayerGuid& aGuid) override;
+
+  void NotifyScaleGestureComplete(const ScrollableLayerGuid& aGuid,
+                                  float aScale) override;
+
+  bool IsRepaintThread() override;
+
+  void DispatchToRepaintThread(already_AddRefed<Runnable> aTask) override;
+
+  PresShell* GetTopLevelPresShell() const override;
+
+ private:
+  RefPtr<dom::BrowserChild> mBrowser;
+};
+
+}  // namespace layers
+
+}  // namespace mozilla
+
+#endif  // mozilla_layers_ContentProcessController_h
diff --git a/gfx/layers/apz/util/DoubleTapToZoom.cpp b/gfx/layers/apz/util/DoubleTapToZoom.cpp
new file mode 100644
index 0000000000..c40d79ced3
--- /dev/null
+++ b/gfx/layers/apz/util/DoubleTapToZoom.cpp
@@ -0,0 +1,376 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "DoubleTapToZoom.h"
+
+#include <algorithm>  // for std::min, std::max
+
+#include "mozilla/PresShell.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/dom/Element.h"
+#include "nsCOMPtr.h"
+#include "nsIContent.h"
+#include "mozilla/dom/Document.h"
+#include "nsIFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsIScrollableFrame.h"
+#include "nsTableCellFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsStyleConsts.h"
+#include "mozilla/ViewportUtils.h"
+#include "mozilla/EventListenerManager.h"
+
+namespace mozilla {
+namespace layers {
+
+namespace {
+
+using FrameForPointOption = nsLayoutUtils::FrameForPointOption;
+
+static bool IsGeneratedContent(nsIContent* aContent) {
+  // We exclude marks because making them double tap targets does not seem
+  // desirable.
+  return aContent->IsGeneratedContentContainerForBefore() ||
+         aContent->IsGeneratedContentContainerForAfter();
+}
+
+// Returns the DOM element found at |aPoint|, interpreted as being relative to
+// the root frame of |aPresShell| in visual coordinates. If the point is inside
+// a subdocument, returns an element inside the subdocument, rather than the
+// subdocument element (and does so recursively). The implementation was adapted
+// from DocumentOrShadowRoot::ElementFromPoint(), with the notable exception
+// that we don't pass nsLayoutUtils::IGNORE_CROSS_DOC to GetFrameForPoint(), so
+// as to get the behaviour described above in the presence of subdocuments.
+static already_AddRefed<dom::Element> ElementFromPoint(
+    const RefPtr<PresShell>& aPresShell, const CSSPoint& aPoint) {
+  nsIFrame* rootFrame = aPresShell->GetRootFrame();
+  if (!rootFrame) {
+    return nullptr;
+  }
+  nsIFrame* frame = nsLayoutUtils::GetFrameForPoint(
+      RelativeTo{rootFrame, ViewportType::Visual}, CSSPoint::ToAppUnits(aPoint),
+      {{FrameForPointOption::IgnorePaintSuppression}});
+  while (frame && (!frame->GetContent() ||
+                   (frame->GetContent()->IsInNativeAnonymousSubtree() &&
+                    !IsGeneratedContent(frame->GetContent())))) {
+    frame = nsLayoutUtils::GetParentOrPlaceholderFor(frame);
+  }
+  if (!frame) {
+    return nullptr;
+  }
+  // FIXME(emilio): This should probably use the flattened tree, GetParent() is
+  // not guaranteed to be an element in presence of shadow DOM.
+  nsIContent* content = frame->GetContent();
+  if (!content) {
+    return nullptr;
+  }
+  if (dom::Element* element = content->GetAsElementOrParentElement()) {
+    return do_AddRef(element);
+  }
+  return nullptr;
+}
+
+// Get table cell from element, parent or grand parent.
+static dom::Element* GetNearbyTableCell(
+    const nsCOMPtr<dom::Element>& aElement) {
+  nsTableCellFrame* tableCell = do_QueryFrame(aElement->GetPrimaryFrame());
+  if (tableCell) {
+    return aElement.get();
+  }
+  if (dom::Element* parent = aElement->GetFlattenedTreeParentElement()) {
+    nsTableCellFrame* tableCell = do_QueryFrame(parent->GetPrimaryFrame());
+    if (tableCell) {
+      return parent;
+    }
+    if (dom::Element* grandParent = parent->GetFlattenedTreeParentElement()) {
+      tableCell = do_QueryFrame(grandParent->GetPrimaryFrame());
+      if (tableCell) {
+        return grandParent;
+      }
+    }
+  }
+  return nullptr;
+}
+
+static bool ShouldZoomToElement(
+    const nsCOMPtr<dom::Element>& aElement,
+    const RefPtr<dom::Document>& aRootContentDocument,
+    nsIScrollableFrame* aRootScrollFrame, const FrameMetrics& aMetrics) {
+  if (nsIFrame* frame = aElement->GetPrimaryFrame()) {
+    if (frame->StyleDisplay()->IsInlineFlow() &&
+        // Replaced elements are suitable zoom targets because they act like
+        // inline-blocks instead of inline. (textarea's are the specific reason
+        // we do this)
+        !frame->IsFrameOfType(nsIFrame::eReplaced)) {
+      return false;
+    }
+  }
+  // Trying to zoom to the html element will just end up scrolling to the start
+  // of the document, return false and we'll run out of elements and just
+  // zoomout (without scrolling to the start).
+  if (aElement->OwnerDoc() == aRootContentDocument &&
+      aElement->IsHTMLElement(nsGkAtoms::html)) {
+    return false;
+  }
+  if (aElement->IsAnyOfHTMLElements(nsGkAtoms::li, nsGkAtoms::q)) {
+    return false;
+  }
+
+  // Ignore elements who are table cells or their parents are table cells, and
+  // they take up less than 30% of page rect width because they are likely cells
+  // in data tables (as opposed to tables used for layout purposes), and we
+  // don't want to zoom to them. This heuristic is quite naive and leaves a lot
+  // to be desired.
+  if (dom::Element* tableCell = GetNearbyTableCell(aElement)) {
+    CSSRect rect =
+        nsLayoutUtils::GetBoundingContentRect(tableCell, aRootScrollFrame);
+    if (rect.width < 0.3 * aMetrics.GetScrollableRect().width) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+// Calculates if zooming to aRect would have almost the same zoom level as
+// aCompositedArea currently has. If so we would want to zoom out instead.
+static bool RectHasAlmostSameZoomLevel(const CSSRect& aRect,
+                                       const CSSRect& aCompositedArea) {
+  // This functions checks to see if the area of the rect visible in the
+  // composition bounds (i.e. the overlapArea variable below) is approximately
+  // the max area of the rect we can show.
+
+  // AsyncPanZoomController::ZoomToRect will adjust the zoom and scroll offset
+  // so that the zoom to rect fills the composited area. If after adjusting the
+  // scroll offset _only_ the rect would fill the composited area we want to
+  // zoom out (we don't want to _just_ scroll, we want to do some amount of
+  // zooming, either in or out it doesn't matter which). So translate both rects
+  // to the same origin and then compute their overlap, which is what the
+  // following calculation does.
+
+  float overlapArea = std::min(aRect.width, aCompositedArea.width) *
+                      std::min(aRect.height, aCompositedArea.height);
+  float availHeight = std::min(
+      aRect.Width() * aCompositedArea.Height() / aCompositedArea.Width(),
+      aRect.Height());
+  float showing = overlapArea / (aRect.Width() * availHeight);
+  float ratioW = aRect.Width() / aCompositedArea.Width();
+  float ratioH = aRect.Height() / aCompositedArea.Height();
+
+  return showing > 0.9 && (ratioW > 0.9 || ratioH > 0.9);
+}
+
+}  // namespace
+
+static CSSRect AddHMargin(const CSSRect& aRect, const CSSCoord& aMargin,
+                          const FrameMetrics& aMetrics) {
+  CSSRect rect =
+      CSSRect(std::max(aMetrics.GetScrollableRect().X(), aRect.X() - aMargin),
+              aRect.Y(), aRect.Width() + 2 * aMargin, aRect.Height());
+  // Constrict the rect to the screen's right edge
+  rect.SetWidth(
+      std::min(rect.Width(), aMetrics.GetScrollableRect().XMost() - rect.X()));
+  return rect;
+}
+
+static CSSRect AddVMargin(const CSSRect& aRect, const CSSCoord& aMargin,
+                          const FrameMetrics& aMetrics) {
+  CSSRect rect =
+      CSSRect(aRect.X(),
+              std::max(aMetrics.GetScrollableRect().Y(), aRect.Y() - aMargin),
+              aRect.Width(), aRect.Height() + 2 * aMargin);
+  // Constrict the rect to the screen's bottom edge
+  rect.SetHeight(
+      std::min(rect.Height(), aMetrics.GetScrollableRect().YMost() - rect.Y()));
+  return rect;
+}
+
+static bool IsReplacedElement(const nsCOMPtr<dom::Element>& aElement) {
+  if (nsIFrame* frame = aElement->GetPrimaryFrame()) {
+    if (frame->IsFrameOfType(nsIFrame::eReplaced)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool HasNonPassiveWheelListenerOnAncestor(nsIContent* aContent) {
+  for (nsIContent* content = aContent; content;
+       content = content->GetFlattenedTreeParent()) {
+    EventListenerManager* elm = content->GetExistingListenerManager();
+    if (elm && elm->HasNonPassiveWheelListener()) {
+      return true;
+    }
+  }
+  return false;
+}
+
+ZoomTarget CalculateRectToZoomTo(
+    const RefPtr<dom::Document>& aRootContentDocument, const CSSPoint& aPoint) {
+  // Ensure the layout information we get is up-to-date.
+  aRootContentDocument->FlushPendingNotifications(FlushType::Layout);
+
+  // An empty rect as return value is interpreted as "zoom out".
+  const CSSRect zoomOut;
+
+  RefPtr<PresShell> presShell = aRootContentDocument->GetPresShell();
+  if (!presShell) {
+    return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn};
+  }
+
+  nsIScrollableFrame* rootScrollFrame =
+      presShell->GetRootScrollFrameAsScrollable();
+  if (!rootScrollFrame) {
+    return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn};
+  }
+
+  CSSPoint documentRelativePoint =
+      CSSPoint::FromAppUnits(ViewportUtils::VisualToLayout(
+          CSSPoint::ToAppUnits(aPoint), presShell)) +
+      CSSPoint::FromAppUnits(rootScrollFrame->GetScrollPosition());
+
+  nsCOMPtr<dom::Element> element = ElementFromPoint(presShell, aPoint);
+  if (!element) {
+    return ZoomTarget{zoomOut, CantZoomOutBehavior::ZoomIn, Nothing(),
+                      Some(documentRelativePoint)};
+  }
+
+  CantZoomOutBehavior cantZoomOutBehavior =
+      HasNonPassiveWheelListenerOnAncestor(element)
+          ? CantZoomOutBehavior::Nothing
+          : CantZoomOutBehavior::ZoomIn;
+
+  FrameMetrics metrics =
+      nsLayoutUtils::CalculateBasicFrameMetrics(rootScrollFrame);
+
+  while (element && !ShouldZoomToElement(element, aRootContentDocument,
+                                         rootScrollFrame, metrics)) {
+    element = element->GetFlattenedTreeParentElement();
+  }
+
+  if (!element) {
+    return ZoomTarget{zoomOut, cantZoomOutBehavior, Nothing(),
+                      Some(documentRelativePoint)};
+  }
+
+  CSSPoint visualScrollOffset = metrics.GetVisualScrollOffset();
+  CSSRect compositedArea(visualScrollOffset,
+                         metrics.CalculateCompositedSizeInCssPixels());
+  Maybe<CSSRect> nearestScrollClip;
+  CSSRect rect = nsLayoutUtils::GetBoundingContentRect(element, rootScrollFrame,
+                                                       &nearestScrollClip);
+
+  // In some cases, like overflow: visible and overflowing content, the bounding
+  // client rect of the targeted element won't contain the point the user double
+  // tapped on. In that case we use the scrollable overflow rect if it contains
+  // the user point.
+  if (!rect.Contains(documentRelativePoint)) {
+    if (nsIFrame* scrolledFrame = rootScrollFrame->GetScrolledFrame()) {
+      if (nsIFrame* f = element->GetPrimaryFrame()) {
+        nsRect overflowRect = f->ScrollableOverflowRect();
+        nsLayoutUtils::TransformResult res =
+            nsLayoutUtils::TransformRect(f, scrolledFrame, overflowRect);
+        MOZ_ASSERT(res == nsLayoutUtils::TRANSFORM_SUCCEEDED ||
+                   res == nsLayoutUtils::NONINVERTIBLE_TRANSFORM);
+        if (res == nsLayoutUtils::TRANSFORM_SUCCEEDED) {
+          CSSRect overflowRectCSS = CSSRect::FromAppUnits(overflowRect);
+          if (nearestScrollClip.isSome()) {
+            overflowRectCSS = nearestScrollClip->Intersect(overflowRectCSS);
+          }
+          if (overflowRectCSS.Contains(documentRelativePoint)) {
+            rect = overflowRectCSS;
+          }
+        }
+      }
+    }
+  }
+
+  CSSRect elementBoundingRect = rect;
+
+  // Generally we zoom to the width of some element, but sometimes we zoom to
+  // the height. We set this to true when that happens so that we can add a
+  // vertical margin to the rect, otherwise it looks weird.
+  bool heightConstrained = false;
+
+  // If the element is taller than the visible area of the page scale
+  // the height of the |rect| so that it has the same aspect ratio as
+  // the root frame.  The clipped |rect| is centered on the y value of
+  // the touch point. This allows tall narrow elements to be zoomed.
+  if (!rect.IsEmpty() && compositedArea.Width() > 0.0f &&
+      compositedArea.Height() > 0.0f) {
+    // Calculate the height of the rect if it had the same aspect ratio as
+    // compositedArea.
+    const float widthRatio = rect.Width() / compositedArea.Width();
+    float targetHeight = compositedArea.Height() * widthRatio;
+
+    // We don't want to cut off the top or bottoms of replaced elements that are
+    // square or wider in aspect ratio.
+
+    // If it's a replaced element and we would otherwise trim it's height below
+    if (IsReplacedElement(element) && targetHeight < rect.Height() &&
+        // If the target rect is at most 1.1x away from being square or wider
+        // aspect ratio
+        rect.Height() < 1.1 * rect.Width() &&
+        // and our compositedArea is wider than it is tall
+        compositedArea.Width() >= compositedArea.Height()) {
+      heightConstrained = true;
+      // Expand the width of the rect so that it fills compositedArea so that if
+      // we are already zoomed to this element then the IsRectZoomedIn call
+      // below returns true so that we zoom out. This won't change what we
+      // actually zoom to as we are just making the rect the same aspect ratio
+      // as compositedArea.
+      float targetWidth =
+          rect.Height() * compositedArea.Width() / compositedArea.Height();
+      MOZ_ASSERT(targetWidth > rect.Width());
+      if (targetWidth > rect.Width()) {
+        rect.x -= (targetWidth - rect.Width()) / 2;
+        rect.SetWidth(targetWidth);
+        // keep elementBoundingRect containing rect
+        elementBoundingRect = rect;
+      }
+
+    } else if (targetHeight < rect.Height()) {
+      // Trim the height so that the target rect has the same aspect ratio as
+      // compositedArea, centering it around the user tap point.
+      float newY = documentRelativePoint.y - (targetHeight * 0.5f);
+      if ((newY + targetHeight) > rect.YMost()) {
+        rect.MoveByY(rect.Height() - targetHeight);
+      } else if (newY > rect.Y()) {
+        rect.MoveToY(newY);
+      }
+      rect.SetHeight(targetHeight);
+    }
+  }
+
+  const CSSCoord margin = 15;
+  rect = AddHMargin(rect, margin, metrics);
+
+  if (heightConstrained) {
+    rect = AddVMargin(rect, margin, metrics);
+  }
+
+  // If the rect is already taking up most of the visible area and is
+  // stretching the width of the page, then we want to zoom out instead.
+  if (RectHasAlmostSameZoomLevel(rect, compositedArea)) {
+    return ZoomTarget{zoomOut, cantZoomOutBehavior, Nothing(),
+                      Some(documentRelativePoint)};
+  }
+
+  elementBoundingRect = AddHMargin(elementBoundingRect, margin, metrics);
+
+  // Unlike rect, elementBoundingRect is the full height of the element we are
+  // zooming to. If we zoom to it without a margin it can look a weird, so give
+  // it a vertical margin.
+  elementBoundingRect = AddVMargin(elementBoundingRect, margin, metrics);
+
+  rect.Round();
+  elementBoundingRect.Round();
+  return ZoomTarget{rect, cantZoomOutBehavior, Some(elementBoundingRect),
+                    Some(documentRelativePoint)};
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/DoubleTapToZoom.h b/gfx/layers/apz/util/DoubleTapToZoom.h
new file mode 100644
index 0000000000..91264deef9
--- /dev/null
+++ b/gfx/layers/apz/util/DoubleTapToZoom.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_DoubleTapToZoom_h
+#define mozilla_layers_DoubleTapToZoom_h
+
+#include "Units.h"
+
+template <class T>
+class RefPtr;
+
+namespace mozilla {
+namespace dom {
+class Document;
+}
+
+namespace layers {
+
+enum class CantZoomOutBehavior : int8_t { Nothing = 0, ZoomIn };
+
+struct ZoomTarget {
+  // The preferred target rect that we'd like to zoom in on, if possible. An
+  // empty rect means the browser should zoom out.
+  CSSRect targetRect;
+
+  // If we are asked to zoom out but cannot (due to zoom constraints, etc), then
+  // zoom in some small amount to provide feedback to the user.
+  CantZoomOutBehavior cantZoomOutBehavior = CantZoomOutBehavior::Nothing;
+
+  // If zooming all the way in on |targetRect| is not possible (for example, due
+  // to a max zoom constraint), |elementBoundingRect| may be used to inform a
+  // more optimal target scroll position (for example, we may try to maximize
+  // the area of |elementBoundingRect| that's showing, while keeping
+  // |targetRect| in view and keeping the zoom as close to the desired zoom as
+  // possible).
+  Maybe<CSSRect> elementBoundingRect;
+
+  // The document relative (ie if the content inside the root scroll frame
+  // existed without that scroll frame) pointer position at the time of the
+  // double tap or location of the double tap if we can compute it. Only used if
+  // the rest of this ZoomTarget is asking to zoom out but we are already at the
+  // minimum zoom. In which case we zoom in a small amount on this point.
+  Maybe<CSSPoint> documentRelativePointerPosition;
+};
+
+/**
+ * For a double tap at |aPoint|, return a ZoomTarget struct with contains a rect
+ * to which the browser should zoom in response (see ZoomTarget definition for
+ * more details). An empty rect means the browser should zoom out. |aDocument|
+ * should be the root content document for the content that was tapped.
+ */
+ZoomTarget CalculateRectToZoomTo(
+    const RefPtr<mozilla::dom::Document>& aRootContentDocument,
+    const CSSPoint& aPoint);
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_DoubleTapToZoom_h */
diff --git a/gfx/layers/apz/util/InputAPZContext.cpp b/gfx/layers/apz/util/InputAPZContext.cpp
new file mode 100644
index 0000000000..77573221ff
--- /dev/null
+++ b/gfx/layers/apz/util/InputAPZContext.cpp
@@ -0,0 +1,65 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "InputAPZContext.h"
+
+namespace mozilla {
+namespace layers {
+
+ScrollableLayerGuid InputAPZContext::sGuid;
+uint64_t InputAPZContext::sBlockId = 0;
+nsEventStatus InputAPZContext::sApzResponse = nsEventStatus_eSentinel;
+bool InputAPZContext::sPendingLayerization = false;
+bool InputAPZContext::sRoutedToChildProcess = false;
+
+/*static*/
+ScrollableLayerGuid InputAPZContext::GetTargetLayerGuid() { return sGuid; }
+
+/*static*/
+uint64_t InputAPZContext::GetInputBlockId() { return sBlockId; }
+
+/*static*/
+nsEventStatus InputAPZContext::GetApzResponse() { return sApzResponse; }
+
+/*static*/
+bool InputAPZContext::HavePendingLayerization() { return sPendingLayerization; }
+
+/*static*/
+bool InputAPZContext::WasRoutedToChildProcess() {
+  return sRoutedToChildProcess;
+}
+
+InputAPZContext::InputAPZContext(const ScrollableLayerGuid& aGuid,
+                                 const uint64_t& aBlockId,
+                                 const nsEventStatus& aApzResponse,
+                                 bool aPendingLayerization)
+    : mOldGuid(sGuid),
+      mOldBlockId(sBlockId),
+      mOldApzResponse(sApzResponse),
+      mOldPendingLayerization(sPendingLayerization),
+      mOldRoutedToChildProcess(sRoutedToChildProcess) {
+  sGuid = aGuid;
+  sBlockId = aBlockId;
+  sApzResponse = aApzResponse;
+  sPendingLayerization = aPendingLayerization;
+  sRoutedToChildProcess = false;
+}
+
+InputAPZContext::~InputAPZContext() {
+  sGuid = mOldGuid;
+  sBlockId = mOldBlockId;
+  sApzResponse = mOldApzResponse;
+  sPendingLayerization = mOldPendingLayerization;
+  sRoutedToChildProcess = mOldRoutedToChildProcess;
+}
+
+/*static*/
+void InputAPZContext::SetRoutedToChildProcess() {
+  sRoutedToChildProcess = true;
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/InputAPZContext.h b/gfx/layers/apz/util/InputAPZContext.h
new file mode 100644
index 0000000000..928359ab1d
--- /dev/null
+++ b/gfx/layers/apz/util/InputAPZContext.h
@@ -0,0 +1,69 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_InputAPZContext_h
+#define mozilla_layers_InputAPZContext_h
+
+#include "mozilla/EventForwards.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+
+namespace mozilla {
+namespace layers {
+
+// InputAPZContext is used to communicate various pieces of information
+// around the codebase without having to plumb it through lots of functions
+// and codepaths. Conceptually it is attached to a WidgetInputEvent that is
+// relevant to APZ.
+//
+// There are two types of information bits propagated using this class. One
+// type is propagated "downwards" (from a process entry point like nsBaseWidget
+// or BrowserChild) into deeper code that is run during complicated operations
+// like event dispatch. The other type is information that is propagated
+// "upwards", from the deeper code back to the entry point.
+class MOZ_STACK_CLASS InputAPZContext {
+ private:
+  // State that is propagated downwards from InputAPZContext creation into
+  // "deeper" code.
+  static ScrollableLayerGuid sGuid;
+  static uint64_t sBlockId;
+  static nsEventStatus sApzResponse;
+  static bool sPendingLayerization;
+
+  // State that is set in deeper code and propagated upwards.
+  static bool sRoutedToChildProcess;
+
+ public:
+  // Functions to access downwards-propagated data
+  static ScrollableLayerGuid GetTargetLayerGuid();
+  static uint64_t GetInputBlockId();
+  static nsEventStatus GetApzResponse();
+  static bool HavePendingLayerization();
+
+  // Functions to access upwards-propagated data
+  static bool WasRoutedToChildProcess();
+
+  // Constructor sets the data to be propagated downwards
+  InputAPZContext(const ScrollableLayerGuid& aGuid, const uint64_t& aBlockId,
+                  const nsEventStatus& aApzResponse,
+                  bool aPendingLayerization = false);
+  ~InputAPZContext();
+
+  // Functions to set data to be propagated upwards
+  static void SetRoutedToChildProcess();
+
+ private:
+  ScrollableLayerGuid mOldGuid;
+  uint64_t mOldBlockId;
+  nsEventStatus mOldApzResponse;
+  bool mOldPendingLayerization;
+
+  bool mOldRoutedToChildProcess;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_InputAPZContext_h */
diff --git a/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp b/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp
new file mode 100644
index 0000000000..eb456fa243
--- /dev/null
+++ b/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "ScrollLinkedEffectDetector.h"
+
+#include "mozilla/dom/Document.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+namespace layers {
+
+uint32_t ScrollLinkedEffectDetector::sDepth = 0;
+bool ScrollLinkedEffectDetector::sFoundScrollLinkedEffect = false;
+
+/* static */
+void ScrollLinkedEffectDetector::PositioningPropertyMutated() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (sDepth > 0) {
+    // We are inside a scroll event dispatch
+    sFoundScrollLinkedEffect = true;
+  }
+}
+
+ScrollLinkedEffectDetector::ScrollLinkedEffectDetector(
+    dom::Document* aDoc, const TimeStamp& aTimeStamp)
+    : mDocument(aDoc), mTimeStamp(aTimeStamp) {
+  MOZ_ASSERT(NS_IsMainThread());
+  sDepth++;
+}
+
+ScrollLinkedEffectDetector::~ScrollLinkedEffectDetector() {
+  sDepth--;
+  if (sDepth == 0) {
+    // We have exited all (possibly-nested) scroll event dispatches,
+    // record whether or not we found an effect, and reset state
+    if (sFoundScrollLinkedEffect) {
+      mDocument->ReportHasScrollLinkedEffect(mTimeStamp);
+      sFoundScrollLinkedEffect = false;
+    }
+  }
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/ScrollLinkedEffectDetector.h b/gfx/layers/apz/util/ScrollLinkedEffectDetector.h
new file mode 100644
index 0000000000..4568fe649b
--- /dev/null
+++ b/gfx/layers/apz/util/ScrollLinkedEffectDetector.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_ScrollLinkedEffectDetector_h
+#define mozilla_layers_ScrollLinkedEffectDetector_h
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/TimeStamp.h"
+
+namespace mozilla {
+
+namespace dom {
+class Document;
+}
+
+namespace layers {
+
+// ScrollLinkedEffectDetector is used to detect the existence of a scroll-linked
+// effect on a webpage. Generally speaking, a scroll-linked effect is something
+// on the page that animates or changes with respect to the scroll position.
+// Content authors usually rely on running some JS in response to the scroll
+// event in order to implement such effects, and therefore it tends to be laggy
+// or work improperly with APZ enabled. This class helps us detect such an
+// effect so that we can warn the author and/or take other preventative
+// measures.
+class MOZ_STACK_CLASS ScrollLinkedEffectDetector final {
+ private:
+  static uint32_t sDepth;
+  static bool sFoundScrollLinkedEffect;
+
+ public:
+  static void PositioningPropertyMutated();
+
+  ScrollLinkedEffectDetector(dom::Document*, const TimeStamp& aTimeStamp);
+  ~ScrollLinkedEffectDetector();
+
+ private:
+  RefPtr<dom::Document> mDocument;
+  TimeStamp mTimeStamp;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_ScrollLinkedEffectDetector_h */
diff --git a/gfx/layers/apz/util/ScrollingInteractionContext.cpp b/gfx/layers/apz/util/ScrollingInteractionContext.cpp
new file mode 100644
index 0000000000..1a92a9eb07
--- /dev/null
+++ b/gfx/layers/apz/util/ScrollingInteractionContext.cpp
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "ScrollingInteractionContext.h"
+
+namespace mozilla::layers {
+
+/*static*/
+bool ScrollingInteractionContext::sScrollingToAnchor = false;
+
+/*static*/
+bool ScrollingInteractionContext::IsScrollingToAnchor() {
+  return sScrollingToAnchor;
+}
+
+ScrollingInteractionContext::ScrollingInteractionContext(
+    bool aScrollingToAnchor)
+    : mOldScrollingToAnchor(sScrollingToAnchor) {
+  sScrollingToAnchor = aScrollingToAnchor;
+}
+
+ScrollingInteractionContext::~ScrollingInteractionContext() {
+  sScrollingToAnchor = mOldScrollingToAnchor;
+}
+
+}  // namespace mozilla::layers
diff --git a/gfx/layers/apz/util/ScrollingInteractionContext.h b/gfx/layers/apz/util/ScrollingInteractionContext.h
new file mode 100644
index 0000000000..cae953008b
--- /dev/null
+++ b/gfx/layers/apz/util/ScrollingInteractionContext.h
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_ScrollingInteractionContext_h
+#define mozilla_layers_ScrollingInteractionContext_h
+
+#include "mozilla/EventForwards.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+
+namespace mozilla {
+namespace layers {
+
+// The ScrollingInteractionContext is used to store minor details of the
+// current scrolling interaction on the stack to avoid having to pass them
+// though the callstack
+class MOZ_STACK_CLASS ScrollingInteractionContext {
+ private:
+  static bool sScrollingToAnchor;
+
+ public:
+  // Functions to access downwards-propagated data
+  static bool IsScrollingToAnchor();
+
+  // Constructor sets the data to be propagated downwards
+  explicit ScrollingInteractionContext(bool aScrollingToAnchor);
+
+  // Destructor restores the previous state
+  ~ScrollingInteractionContext();
+
+ private:
+  bool mOldScrollingToAnchor;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_ScrollingInteractionContext_h */
diff --git a/gfx/layers/apz/util/TouchActionHelper.cpp b/gfx/layers/apz/util/TouchActionHelper.cpp
new file mode 100644
index 0000000000..4598e30a6a
--- /dev/null
+++ b/gfx/layers/apz/util/TouchActionHelper.cpp
@@ -0,0 +1,131 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "TouchActionHelper.h"
+
+#include "mozilla/layers/IAPZCTreeManager.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/TouchEvents.h"
+#include "nsContainerFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsIScrollableFrame.h"
+#include "nsLayoutUtils.h"
+
+namespace mozilla::layers {
+
+static void UpdateAllowedBehavior(StyleTouchAction aTouchActionValue,
+                                  bool aConsiderPanning,
+                                  TouchBehaviorFlags& aOutBehavior) {
+  if (aTouchActionValue != StyleTouchAction::AUTO) {
+    // Double-tap-zooming need property value AUTO
+    aOutBehavior &= ~AllowedTouchBehavior::ANIMATING_ZOOM;
+    if (aTouchActionValue != StyleTouchAction::MANIPULATION &&
+        !(aTouchActionValue & StyleTouchAction::PINCH_ZOOM)) {
+      // Pinch-zooming needs value AUTO or MANIPULATION, or the PINCH_ZOOM bit
+      // set
+      aOutBehavior &= ~AllowedTouchBehavior::PINCH_ZOOM;
+    }
+  }
+
+  if (aConsiderPanning) {
+    if (aTouchActionValue == StyleTouchAction::NONE) {
+      aOutBehavior &= ~AllowedTouchBehavior::VERTICAL_PAN;
+      aOutBehavior &= ~AllowedTouchBehavior::HORIZONTAL_PAN;
+    }
+
+    // Values pan-x and pan-y set at the same time to the same element do not
+    // affect panning constraints. Therefore we need to check whether pan-x is
+    // set without pan-y and the same for pan-y.
+    if ((aTouchActionValue & StyleTouchAction::PAN_X) &&
+        !(aTouchActionValue & StyleTouchAction::PAN_Y)) {
+      aOutBehavior &= ~AllowedTouchBehavior::VERTICAL_PAN;
+    } else if ((aTouchActionValue & StyleTouchAction::PAN_Y) &&
+               !(aTouchActionValue & StyleTouchAction::PAN_X)) {
+      aOutBehavior &= ~AllowedTouchBehavior::HORIZONTAL_PAN;
+    }
+  }
+}
+
+static TouchBehaviorFlags GetAllowedTouchBehaviorForPoint(
+    nsIWidget* aWidget, RelativeTo aRootFrame,
+    const LayoutDeviceIntPoint& aPoint) {
+  nsPoint relativePoint =
+      nsLayoutUtils::GetEventCoordinatesRelativeTo(aWidget, aPoint, aRootFrame);
+
+  nsIFrame* target = nsLayoutUtils::GetFrameForPoint(aRootFrame, relativePoint);
+
+  return TouchActionHelper::GetAllowedTouchBehaviorForFrame(target);
+}
+
+nsTArray<TouchBehaviorFlags> TouchActionHelper::GetAllowedTouchBehavior(
+    nsIWidget* aWidget, dom::Document* aDocument,
+    const WidgetTouchEvent& aEvent) {
+  nsTArray<TouchBehaviorFlags> flags;
+  if (!aWidget || !aDocument) {
+    return flags;
+  }
+  if (PresShell* presShell = aDocument->GetPresShell()) {
+    if (nsIFrame* rootFrame = presShell->GetRootFrame()) {
+      for (const auto& touch : aEvent.mTouches) {
+        flags.AppendElement(GetAllowedTouchBehaviorForPoint(
+            aWidget, RelativeTo{rootFrame, ViewportType::Visual},
+            touch->mRefPoint));
+      }
+    }
+  }
+  return flags;
+}
+
+TouchBehaviorFlags TouchActionHelper::GetAllowedTouchBehaviorForFrame(
+    nsIFrame* aFrame) {
+  TouchBehaviorFlags behavior = AllowedTouchBehavior::VERTICAL_PAN |
+                                AllowedTouchBehavior::HORIZONTAL_PAN |
+                                AllowedTouchBehavior::PINCH_ZOOM |
+                                AllowedTouchBehavior::ANIMATING_ZOOM;
+
+  if (!aFrame) {
+    return behavior;
+  }
+
+  nsIScrollableFrame* nearestScrollableParent =
+      nsLayoutUtils::GetNearestScrollableFrame(aFrame, 0);
+  nsIFrame* nearestScrollableFrame = do_QueryFrame(nearestScrollableParent);
+
+  // We're walking up the DOM tree until we meet the element with touch behavior
+  // and accumulating touch-action restrictions of all elements in this chain.
+  // The exact quote from the spec, that clarifies more:
+  // To determine the effect of a touch, find the nearest ancestor (starting
+  // from the element itself) that has a default touch behavior. Then examine
+  // the touch-action property of each element between the hit tested element
+  // and the element with the default touch behavior (including both the hit
+  // tested element and the element with the default touch behavior). If the
+  // touch-action property of any of those elements disallows the default touch
+  // behavior, do nothing. Otherwise allow the element to start considering the
+  // touch for the purposes of executing a default touch behavior.
+
+  // Currently we support only two touch behaviors: panning and zooming.
+  // For panning we walk up until we meet the first scrollable element (the
+  // element that supports panning) or root element. For zooming we walk up
+  // until the root element since Firefox currently supports only zooming of the
+  // root frame but not the subframes.
+
+  bool considerPanning = true;
+
+  for (nsIFrame* frame = aFrame; frame && frame->GetContent() && behavior;
+       frame = frame->GetInFlowParent()) {
+    UpdateAllowedBehavior(frame->UsedTouchAction(), considerPanning, behavior);
+
+    if (frame == nearestScrollableFrame) {
+      // We met the scrollable element, after it we shouldn't consider
+      // touch-action values for the purpose of panning but only for zooming.
+      considerPanning = false;
+    }
+  }
+
+  return behavior;
+}
+
+}  // namespace mozilla::layers
diff --git a/gfx/layers/apz/util/TouchActionHelper.h b/gfx/layers/apz/util/TouchActionHelper.h
new file mode 100644
index 0000000000..b83d0d9ecb
--- /dev/null
+++ b/gfx/layers/apz/util/TouchActionHelper.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef __mozilla_layers_TouchActionHelper_h__
+#define __mozilla_layers_TouchActionHelper_h__
+
+#include "mozilla/layers/LayersTypes.h"  // for TouchBehaviorFlags
+#include "RelativeTo.h"                  // for RelativeTo
+
+class nsIWidget;
+namespace mozilla {
+
+namespace dom {
+class Document;
+}  // namespace dom
+
+class WidgetTouchEvent;
+}  // namespace mozilla
+
+namespace mozilla::layers {
+
+/*
+ * Helper class to figure out the allowed touch behavior for frames, as per
+ * the touch-action spec.
+ */
+class TouchActionHelper {
+ public:
+  /*
+   * Performs hit testing on content, finds frame that corresponds to the touch
+   * points of aEvent and retrieves touch-action CSS property value from it
+   * according the rules specified in the spec:
+   * http://www.w3.org/TR/pointerevents/#the-touch-action-css-property.
+   */
+  static nsTArray<TouchBehaviorFlags> GetAllowedTouchBehavior(
+      nsIWidget* aWidget, dom::Document* aDocument,
+      const WidgetTouchEvent& aPoint);
+
+  static TouchBehaviorFlags GetAllowedTouchBehaviorForFrame(nsIFrame* aFrame);
+};
+
+}  // namespace mozilla::layers
+
+#endif /*__mozilla_layers_TouchActionHelper_h__ */
diff --git a/gfx/layers/apz/util/TouchCounter.cpp b/gfx/layers/apz/util/TouchCounter.cpp
new file mode 100644
index 0000000000..9e4d6f1ba6
--- /dev/null
+++ b/gfx/layers/apz/util/TouchCounter.cpp
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "TouchCounter.h"
+
+#include "InputData.h"
+#include "mozilla/TouchEvents.h"
+
+namespace mozilla {
+namespace layers {
+
+TouchCounter::TouchCounter() : mActiveTouchCount(0) {}
+
+void TouchCounter::Update(const MultiTouchInput& aInput) {
+  switch (aInput.mType) {
+    case MultiTouchInput::MULTITOUCH_START:
+      // touch-start event contains all active touches of the current session
+      mActiveTouchCount = aInput.mTouches.Length();
+      break;
+    case MultiTouchInput::MULTITOUCH_END:
+      if (mActiveTouchCount >= aInput.mTouches.Length()) {
+        // touch-end event contains only released touches
+        mActiveTouchCount -= aInput.mTouches.Length();
+      } else {
+        NS_WARNING("Got an unexpected touchend");
+        mActiveTouchCount = 0;
+      }
+      break;
+    case MultiTouchInput::MULTITOUCH_CANCEL:
+      mActiveTouchCount = 0;
+      break;
+    case MultiTouchInput::MULTITOUCH_MOVE:
+      break;
+  }
+}
+
+void TouchCounter::Update(const WidgetTouchEvent& aEvent) {
+  switch (aEvent.mMessage) {
+    case eTouchStart:
+      // touch-start event contains all active touches of the current session
+      mActiveTouchCount = aEvent.mTouches.Length();
+      break;
+    case eTouchEnd: {
+      // touch-end contains all touches, but ones being lifted are marked as
+      // changed
+      uint32_t liftedTouches = 0;
+      for (const auto& touch : aEvent.mTouches) {
+        if (touch->mChanged) {
+          liftedTouches++;
+        }
+      }
+      if (mActiveTouchCount >= liftedTouches) {
+        mActiveTouchCount -= liftedTouches;
+      } else {
+        NS_WARNING("Got an unexpected touchend");
+        mActiveTouchCount = 0;
+      }
+      break;
+    }
+    case eTouchCancel:
+      mActiveTouchCount = 0;
+      break;
+    default:
+      break;
+  }
+}
+
+uint32_t TouchCounter::GetActiveTouchCount() const { return mActiveTouchCount; }
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/util/TouchCounter.h b/gfx/layers/apz/util/TouchCounter.h
new file mode 100644
index 0000000000..c13f475355
--- /dev/null
+++ b/gfx/layers/apz/util/TouchCounter.h
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_layers_TouchCounter_h
+#define mozilla_layers_TouchCounter_h
+
+#include "mozilla/EventForwards.h"
+
+namespace mozilla {
+
+class MultiTouchInput;
+
+namespace layers {
+
+// TouchCounter simply tracks the number of active touch points. Feed it
+// your input events to update the internal state. Generally you should
+// only be calling one of the Update functions, depending on which type
+// of touch inputs you have access to.
+class TouchCounter {
+ public:
+  TouchCounter();
+  void Update(const MultiTouchInput& aInput);
+  void Update(const WidgetTouchEvent& aEvent);
+  uint32_t GetActiveTouchCount() const;
+
+ private:
+  uint32_t mActiveTouchCount;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_TouchCounter_h */