Adding upstream version 110.0.1.upstream/110.0.1upstream

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

30 files changed, 10649 insertions, 0 deletions

diff --git a/gfx/layers/apz/test/gtest/APZCBasicTester.h b/gfx/layers/apz/test/gtest/APZCBasicTester.h
new file mode 100644
index 0000000000..621a3d37be
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/APZCBasicTester.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_APZCBasicTester_h
+#define mozilla_layers_APZCBasicTester_h
+
+/**
+ * Defines a test fixture used for testing a single APZC.
+ */
+
+#include "APZTestCommon.h"
+
+#include "mozilla/layers/APZSampler.h"
+#include "mozilla/layers/APZUpdater.h"
+
+class APZCBasicTester : public APZCTesterBase {
+ public:
+  explicit APZCBasicTester(
+      AsyncPanZoomController::GestureBehavior aGestureBehavior =
+          AsyncPanZoomController::DEFAULT_GESTURES)
+      : mGestureBehavior(aGestureBehavior) {}
+
+ protected:
+  virtual void SetUp() {
+    APZCTesterBase::SetUp();
+    APZThreadUtils::SetThreadAssertionsEnabled(false);
+    APZThreadUtils::SetControllerThread(NS_GetCurrentThread());
+
+    tm = new TestAPZCTreeManager(mcc);
+    updater = new APZUpdater(tm, false);
+    sampler = new APZSampler(tm, false);
+    apzc =
+        new TestAsyncPanZoomController(LayersId{0}, mcc, tm, mGestureBehavior);
+    apzc->SetFrameMetrics(TestFrameMetrics());
+    apzc->GetScrollMetadata().SetIsLayersIdRoot(true);
+  }
+
+  /**
+   * Get the APZC's scroll range in CSS pixels.
+   */
+  CSSRect GetScrollRange() const {
+    const FrameMetrics& metrics = apzc->GetFrameMetrics();
+    return CSSRect(metrics.GetScrollableRect().TopLeft(),
+                   metrics.GetScrollableRect().Size() -
+                       metrics.CalculateCompositedSizeInCssPixels());
+  }
+
+  virtual void TearDown() {
+    while (mcc->RunThroughDelayedTasks())
+      ;
+    apzc->Destroy();
+    tm->ClearTree();
+    tm->ClearContentController();
+
+    APZCTesterBase::TearDown();
+  }
+
+  void MakeApzcWaitForMainThread() { apzc->SetWaitForMainThread(); }
+
+  void MakeApzcZoomable() {
+    apzc->UpdateZoomConstraints(ZoomConstraints(
+        true, true, CSSToParentLayerScale(0.25f), CSSToParentLayerScale(4.0f)));
+  }
+
+  void MakeApzcUnzoomable() {
+    apzc->UpdateZoomConstraints(ZoomConstraints(false, false,
+                                                CSSToParentLayerScale(1.0f),
+                                                CSSToParentLayerScale(1.0f)));
+  }
+
+  /**
+   * Sample animations once, 1 ms later than the last sample.
+   */
+  void SampleAnimationOnce() {
+    const TimeDuration increment = TimeDuration::FromMilliseconds(1);
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+    mcc->AdvanceBy(increment);
+    apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  }
+  /**
+   * Sample animations one frame, 17 ms later than the last sample.
+   */
+  void SampleAnimationOneFrame() {
+    const TimeDuration increment = TimeDuration::FromMilliseconds(17);
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+    mcc->AdvanceBy(increment);
+    apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  }
+
+  AsyncPanZoomController::GestureBehavior mGestureBehavior;
+  RefPtr<TestAPZCTreeManager> tm;
+  RefPtr<APZSampler> sampler;
+  RefPtr<APZUpdater> updater;
+  RefPtr<TestAsyncPanZoomController> apzc;
+};
+
+#endif  // mozilla_layers_APZCBasicTester_h
diff --git a/gfx/layers/apz/test/gtest/APZCTreeManagerTester.h b/gfx/layers/apz/test/gtest/APZCTreeManagerTester.h
new file mode 100644
index 0000000000..8a2f9d749b
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/APZCTreeManagerTester.h
@@ -0,0 +1,223 @@
+/* -*- 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_APZCTreeManagerTester_h
+#define mozilla_layers_APZCTreeManagerTester_h
+
+/**
+ * Defines a test fixture used for testing multiple APZCs interacting in
+ * an APZCTreeManager.
+ */
+
+#include "APZTestAccess.h"
+#include "APZTestCommon.h"
+#include "gfxPlatform.h"
+#include "MockHitTester.h"
+#include "apz/src/WRHitTester.h"
+
+#include "mozilla/layers/APZSampler.h"
+#include "mozilla/layers/APZUpdater.h"
+#include "mozilla/layers/WebRenderScrollDataWrapper.h"
+
+class APZCTreeManagerTester : public APZCTesterBase {
+ protected:
+  APZCTreeManagerTester() : mHitTester(MakeUnique<WRHitTester>()) {}
+
+  virtual void SetUp() {
+    APZCTesterBase::SetUp();
+
+    APZThreadUtils::SetThreadAssertionsEnabled(false);
+    APZThreadUtils::SetControllerThread(NS_GetCurrentThread());
+
+    manager = new TestAPZCTreeManager(mcc, std::move(mHitTester));
+    updater = new APZUpdater(manager, false);
+    sampler = new APZSampler(manager, false);
+  }
+
+  virtual void TearDown() {
+    while (mcc->RunThroughDelayedTasks())
+      ;
+    manager->ClearTree();
+    manager->ClearContentController();
+
+    APZCTesterBase::TearDown();
+  }
+
+  /**
+   * Sample animations once for all APZCs, 1 ms later than the last sample and
+   * return whether there is still any active animations or not.
+   */
+  bool SampleAnimationsOnce() {
+    const TimeDuration increment = TimeDuration::FromMilliseconds(1);
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+    mcc->AdvanceBy(increment);
+
+    bool activeAnimations = false;
+
+    for (size_t i = 0; i < layers.GetLayerCount(); ++i) {
+      if (TestAsyncPanZoomController* apzc = ApzcOf(layers[i])) {
+        activeAnimations |=
+            apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+      }
+    }
+
+    return activeAnimations;
+  }
+
+  // A convenience function for letting a test modify the frame metrics
+  // stored on a particular layer.
+  template <typename Callback>
+  void ModifyFrameMetrics(WebRenderLayerScrollData* aLayer,
+                          Callback aCallback) {
+    MOZ_ASSERT(aLayer->GetScrollMetadataCount() == 1);
+    ScrollMetadata& metadataRef =
+        APZTestAccess::GetScrollMetadataMut(*aLayer, layers, 0);
+    aCallback(metadataRef, metadataRef.GetMetrics());
+  }
+
+  // A convenience wrapper for manager->UpdateHitTestingTree().
+  void UpdateHitTestingTree(uint32_t aPaintSequenceNumber = 0) {
+    manager->UpdateHitTestingTree(WebRenderScrollDataWrapper{*updater, &layers},
+                                  /* is first paint = */ false, LayersId{0},
+                                  aPaintSequenceNumber);
+  }
+
+  void CreateScrollData(const char* aTreeShape,
+                        const LayerIntRegion* aVisibleRegions = nullptr,
+                        const gfx::Matrix4x4* aTransforms = nullptr) {
+    layers = TestWRScrollData::Create(aTreeShape, *updater, aVisibleRegions,
+                                      aTransforms);
+    root = layers[0];
+  }
+
+  void CreateMockHitTester() {
+    mHitTester = MakeUnique<MockHitTester>();
+    // Save a pointer in a separate variable, because SetUp() will
+    // move the value out of mHitTester.
+    mMockHitTester = static_cast<MockHitTester*>(mHitTester.get());
+  }
+  void QueueMockHitResult(ScrollableLayerGuid::ViewID aScrollId,
+                          gfx::CompositorHitTestInfo aHitInfo =
+                              gfx::CompositorHitTestFlags::eVisibleToHitTest) {
+    MOZ_ASSERT(mMockHitTester);
+    mMockHitTester->QueueHitResult(aScrollId, aHitInfo);
+  }
+
+  RefPtr<TestAPZCTreeManager> manager;
+  RefPtr<APZSampler> sampler;
+  RefPtr<APZUpdater> updater;
+  TestWRScrollData layers;
+  WebRenderLayerScrollData* root = nullptr;
+
+  UniquePtr<IAPZHitTester> mHitTester;
+  MockHitTester* mMockHitTester = nullptr;
+
+ protected:
+  static ScrollMetadata BuildScrollMetadata(
+      ScrollableLayerGuid::ViewID aScrollId, const CSSRect& aScrollableRect,
+      const ParentLayerRect& aCompositionBounds) {
+    ScrollMetadata metadata;
+    FrameMetrics& metrics = metadata.GetMetrics();
+    metrics.SetScrollId(aScrollId);
+    // By convention in this test file, START_SCROLL_ID is the root, so mark it
+    // as such.
+    if (aScrollId == ScrollableLayerGuid::START_SCROLL_ID) {
+      metadata.SetIsLayersIdRoot(true);
+    }
+    metrics.SetCompositionBounds(aCompositionBounds);
+    metrics.SetScrollableRect(aScrollableRect);
+    metrics.SetLayoutScrollOffset(CSSPoint(0, 0));
+    metadata.SetPageScrollAmount(LayoutDeviceIntSize(50, 100));
+    metadata.SetLineScrollAmount(LayoutDeviceIntSize(5, 10));
+    return metadata;
+  }
+
+  void SetScrollMetadata(WebRenderLayerScrollData* aLayer,
+                         const ScrollMetadata& aMetadata) {
+    MOZ_ASSERT(aLayer->GetScrollMetadataCount() <= 1,
+               "This function does not support multiple ScrollMetadata on a "
+               "single layer");
+    if (aLayer->GetScrollMetadataCount() == 0) {
+      // Add new metrics
+      aLayer->AppendScrollMetadata(layers, aMetadata);
+    } else {
+      // Overwrite existing metrics
+      ModifyFrameMetrics(
+          aLayer, [&](ScrollMetadata& aSm, FrameMetrics&) { aSm = aMetadata; });
+    }
+  }
+
+  void SetScrollMetadata(WebRenderLayerScrollData* aLayer,
+                         const nsTArray<ScrollMetadata>& aMetadata) {
+    // The reason for this restriction is that WebRenderLayerScrollData does not
+    // have an API to *remove* previous metadata.
+    MOZ_ASSERT(aLayer->GetScrollMetadataCount() == 0,
+               "This function can only be used on layers which do not yet have "
+               "scroll metadata");
+    for (const ScrollMetadata& metadata : aMetadata) {
+      aLayer->AppendScrollMetadata(layers, metadata);
+    }
+  }
+
+  void SetScrollableFrameMetrics(WebRenderLayerScrollData* aLayer,
+                                 ScrollableLayerGuid::ViewID aScrollId,
+                                 CSSRect aScrollableRect = CSSRect(-1, -1, -1,
+                                                                   -1)) {
+    auto localTransform = aLayer->GetTransformTyped() * AsyncTransformMatrix();
+    ParentLayerIntRect compositionBounds =
+        RoundedToInt(localTransform.TransformBounds(
+            LayerRect(aLayer->GetVisibleRegion().GetBounds())));
+    ScrollMetadata metadata = BuildScrollMetadata(
+        aScrollId, aScrollableRect, ParentLayerRect(compositionBounds));
+    SetScrollMetadata(aLayer, metadata);
+  }
+
+  bool HasScrollableFrameMetrics(const WebRenderLayerScrollData* aLayer) const {
+    for (uint32_t i = 0; i < aLayer->GetScrollMetadataCount(); i++) {
+      if (aLayer->GetScrollMetadata(layers, i).GetMetrics().IsScrollable()) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  void SetScrollHandoff(WebRenderLayerScrollData* aChild,
+                        WebRenderLayerScrollData* aParent) {
+    ModifyFrameMetrics(aChild, [&](ScrollMetadata& aSm, FrameMetrics&) {
+      aSm.SetScrollParentId(
+          aParent->GetScrollMetadata(layers, 0).GetMetrics().GetScrollId());
+    });
+  }
+
+  TestAsyncPanZoomController* ApzcOf(WebRenderLayerScrollData* aLayer) {
+    EXPECT_EQ(1u, aLayer->GetScrollMetadataCount());
+    return ApzcOf(aLayer, 0);
+  }
+
+  TestAsyncPanZoomController* ApzcOf(WebRenderLayerScrollData* aLayer,
+                                     uint32_t aIndex) {
+    EXPECT_LT(aIndex, aLayer->GetScrollMetadataCount());
+    // Unlike Layer, WebRenderLayerScrollData does not store the associated
+    // APZCs, so look it up using the tree manager instead.
+    RefPtr<AsyncPanZoomController> apzc = manager->GetTargetAPZC(
+        LayersId{0},
+        aLayer->GetScrollMetadata(layers, aIndex).GetMetrics().GetScrollId());
+    return (TestAsyncPanZoomController*)apzc.get();
+  }
+
+  void CreateSimpleScrollingLayer() {
+    const char* treeShape = "x";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 200, 200),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(layers[0], ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 500, 500));
+  }
+};
+
+#endif  // mozilla_layers_APZCTreeManagerTester_h
diff --git a/gfx/layers/apz/test/gtest/APZTestAccess.cpp b/gfx/layers/apz/test/gtest/APZTestAccess.cpp
new file mode 100644
index 0000000000..d55d7711f8
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/APZTestAccess.cpp
@@ -0,0 +1,27 @@
+/* -*- 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 "APZTestAccess.h"
+#include "mozilla/layers/WebRenderScrollData.h"
+
+namespace mozilla {
+namespace layers {
+
+/*static*/
+void APZTestAccess::InitializeForTest(WebRenderLayerScrollData& aLayer,
+                                      int32_t aDescendantCount) {
+  aLayer.InitializeForTest(aDescendantCount);
+}
+
+/*static*/
+ScrollMetadata& APZTestAccess::GetScrollMetadataMut(
+    WebRenderLayerScrollData& aLayer, WebRenderScrollData& aOwner,
+    size_t aIndex) {
+  return aLayer.GetScrollMetadataMut(aOwner, aIndex);
+}
+
+}  // namespace layers
+}  // namespace mozilla
diff --git a/gfx/layers/apz/test/gtest/APZTestAccess.h b/gfx/layers/apz/test/gtest/APZTestAccess.h
new file mode 100644
index 0000000000..a56fb10a1a
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/APZTestAccess.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_APZTestAccess_h
+#define mozilla_layers_APZTestAccess_h
+
+#include <cstddef>  // for size_t
+#include <cstdint>  // for int32_t
+
+namespace mozilla {
+namespace layers {
+
+struct ScrollMetadata;
+class WebRenderLayerScrollData;
+class WebRenderScrollData;
+
+// The only purpose of this class is to serve as a single type that can be
+// the target of a "friend class" declaration in APZ classes that want to
+// give APZ test code access to their private members.
+// APZ test code can then access those members via this class.
+class APZTestAccess {
+ public:
+  static void InitializeForTest(WebRenderLayerScrollData& aLayer,
+                                int32_t aDescendantCount);
+  static ScrollMetadata& GetScrollMetadataMut(WebRenderLayerScrollData& aLayer,
+                                              WebRenderScrollData& aOwner,
+                                              size_t aIndex);
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif
diff --git a/gfx/layers/apz/test/gtest/APZTestCommon.cpp b/gfx/layers/apz/test/gtest/APZTestCommon.cpp
new file mode 100644
index 0000000000..5276531a26
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/APZTestCommon.cpp
@@ -0,0 +1,15 @@
+/* -*- 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 "APZTestCommon.h"
+
+AsyncPanZoomController* TestAPZCTreeManager::NewAPZCInstance(
+    LayersId aLayersId, GeckoContentController* aController) {
+  MockContentControllerDelayed* mcc =
+      static_cast<MockContentControllerDelayed*>(aController);
+  return new TestAsyncPanZoomController(
+      aLayersId, mcc, this, AsyncPanZoomController::USE_GESTURE_DETECTOR);
+}
diff --git a/gfx/layers/apz/test/gtest/APZTestCommon.h b/gfx/layers/apz/test/gtest/APZTestCommon.h
new file mode 100644
index 0000000000..de47d0d6a5
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/APZTestCommon.h
@@ -0,0 +1,1050 @@
+/* -*- 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_APZTestCommon_h
+#define mozilla_layers_APZTestCommon_h
+
+/**
+ * Defines a set of mock classes and utility functions/classes for
+ * writing APZ gtests.
+ */
+
+#include "gtest/gtest.h"
+#include "gmock/gmock.h"
+
+#include "mozilla/Attributes.h"
+#include "mozilla/layers/GeckoContentController.h"
+#include "mozilla/layers/CompositorBridgeParent.h"
+#include "mozilla/layers/APZThreadUtils.h"
+#include "mozilla/layers/MatrixMessage.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/TypedEnumBits.h"
+#include "mozilla/UniquePtr.h"
+#include "apz/src/APZCTreeManager.h"
+#include "apz/src/AsyncPanZoomController.h"
+#include "apz/src/HitTestingTreeNode.h"
+#include "base/task.h"
+#include "gfxPlatform.h"
+#include "TestWRScrollData.h"
+#include "UnitTransforms.h"
+
+using namespace mozilla;
+using namespace mozilla::gfx;
+using namespace mozilla::layers;
+using ::testing::_;
+using ::testing::AtLeast;
+using ::testing::AtMost;
+using ::testing::InSequence;
+using ::testing::MockFunction;
+using ::testing::NiceMock;
+typedef mozilla::layers::GeckoContentController::TapType TapType;
+
+inline TimeStamp GetStartupTime() {
+  static TimeStamp sStartupTime = TimeStamp::Now();
+  return sStartupTime;
+}
+
+inline uint32_t MillisecondsSinceStartup(TimeStamp aTime) {
+  return (aTime - GetStartupTime()).ToMilliseconds();
+}
+
+// Some helper functions for constructing input event objects suitable to be
+// passed either to an APZC (which expects an transformed point), or to an APZTM
+// (which expects an untransformed point). We handle both cases by setting both
+// the transformed and untransformed fields to the same value.
+inline SingleTouchData CreateSingleTouchData(int32_t aIdentifier,
+                                             const ScreenIntPoint& aPoint) {
+  SingleTouchData touch(aIdentifier, aPoint, ScreenSize(0, 0), 0, 0);
+  touch.mLocalScreenPoint = ParentLayerPoint(aPoint.x, aPoint.y);
+  return touch;
+}
+
+// Convenience wrapper for CreateSingleTouchData() that takes loose coordinates.
+inline SingleTouchData CreateSingleTouchData(int32_t aIdentifier,
+                                             ScreenIntCoord aX,
+                                             ScreenIntCoord aY) {
+  return CreateSingleTouchData(aIdentifier, ScreenIntPoint(aX, aY));
+}
+
+inline PinchGestureInput CreatePinchGestureInput(
+    PinchGestureInput::PinchGestureType aType, const ScreenPoint& aFocus,
+    float aCurrentSpan, float aPreviousSpan, TimeStamp timestamp) {
+  ParentLayerPoint localFocus(aFocus.x, aFocus.y);
+  PinchGestureInput result(aType, PinchGestureInput::UNKNOWN, timestamp,
+                           ExternalPoint(0, 0), aFocus, aCurrentSpan,
+                           aPreviousSpan, 0);
+  return result;
+}
+
+template <class SetArg, class Storage>
+class ScopedGfxSetting {
+ public:
+  ScopedGfxSetting(const std::function<SetArg(void)>& aGetPrefFunc,
+                   const std::function<void(SetArg)>& aSetPrefFunc, SetArg aVal)
+      : mSetPrefFunc(aSetPrefFunc) {
+    mOldVal = aGetPrefFunc();
+    aSetPrefFunc(aVal);
+  }
+
+  ~ScopedGfxSetting() { mSetPrefFunc(mOldVal); }
+
+ private:
+  std::function<void(SetArg)> mSetPrefFunc;
+  Storage mOldVal;
+};
+
+static inline constexpr auto kDefaultTouchBehavior =
+    AllowedTouchBehavior::VERTICAL_PAN | AllowedTouchBehavior::HORIZONTAL_PAN |
+    AllowedTouchBehavior::PINCH_ZOOM | AllowedTouchBehavior::DOUBLE_TAP_ZOOM;
+
+#define FRESH_PREF_VAR_PASTE(id, line) id##line
+#define FRESH_PREF_VAR_EXPAND(id, line) FRESH_PREF_VAR_PASTE(id, line)
+#define FRESH_PREF_VAR FRESH_PREF_VAR_EXPAND(pref, __LINE__)
+
+#define SCOPED_GFX_PREF_BOOL(prefName, prefValue)                           \
+  ScopedGfxSetting<bool, bool> FRESH_PREF_VAR(                              \
+      [=]() { return Preferences::GetBool(prefName); },                     \
+      [=](bool aPrefValue) { Preferences::SetBool(prefName, aPrefValue); }, \
+      prefValue)
+
+#define SCOPED_GFX_PREF_INT(prefName, prefValue)                              \
+  ScopedGfxSetting<int32_t, int32_t> FRESH_PREF_VAR(                          \
+      [=]() { return Preferences::GetInt(prefName); },                        \
+      [=](int32_t aPrefValue) { Preferences::SetInt(prefName, aPrefValue); }, \
+      prefValue)
+
+#define SCOPED_GFX_PREF_FLOAT(prefName, prefValue)                            \
+  ScopedGfxSetting<float, float> FRESH_PREF_VAR(                              \
+      [=]() { return Preferences::GetFloat(prefName); },                      \
+      [=](float aPrefValue) { Preferences::SetFloat(prefName, aPrefValue); }, \
+      prefValue)
+
+class MockContentController : public GeckoContentController {
+ public:
+  MOCK_METHOD1(NotifyLayerTransforms, void(nsTArray<MatrixMessage>&&));
+  MOCK_METHOD1(RequestContentRepaint, void(const RepaintRequest&));
+  MOCK_METHOD5(HandleTap, void(TapType, const LayoutDevicePoint&, Modifiers,
+                               const ScrollableLayerGuid&, uint64_t));
+  MOCK_METHOD5(NotifyPinchGesture,
+               void(PinchGestureInput::PinchGestureType,
+                    const ScrollableLayerGuid&, const LayoutDevicePoint&,
+                    LayoutDeviceCoord, Modifiers));
+  // Can't use the macros with already_AddRefed :(
+  void PostDelayedTask(already_AddRefed<Runnable> aTask, int aDelayMs) {
+    RefPtr<Runnable> task = aTask;
+  }
+  bool IsRepaintThread() { return NS_IsMainThread(); }
+  void DispatchToRepaintThread(already_AddRefed<Runnable> aTask) {
+    NS_DispatchToMainThread(std::move(aTask));
+  }
+  MOCK_METHOD3(NotifyAPZStateChange, void(const ScrollableLayerGuid& aGuid,
+                                          APZStateChange aChange, int aArg));
+  MOCK_METHOD0(NotifyFlushComplete, void());
+  MOCK_METHOD3(NotifyAsyncScrollbarDragInitiated,
+               void(uint64_t, const ScrollableLayerGuid::ViewID&,
+                    ScrollDirection aDirection));
+  MOCK_METHOD1(NotifyAsyncScrollbarDragRejected,
+               void(const ScrollableLayerGuid::ViewID&));
+  MOCK_METHOD1(NotifyAsyncAutoscrollRejected,
+               void(const ScrollableLayerGuid::ViewID&));
+  MOCK_METHOD1(CancelAutoscroll, void(const ScrollableLayerGuid&));
+  MOCK_METHOD2(NotifyScaleGestureComplete,
+               void(const ScrollableLayerGuid&, float aScale));
+  MOCK_METHOD4(UpdateOverscrollVelocity,
+               void(const ScrollableLayerGuid&, float, float, bool));
+  MOCK_METHOD4(UpdateOverscrollOffset,
+               void(const ScrollableLayerGuid&, float, float, bool));
+};
+
+class MockContentControllerDelayed : public MockContentController {
+ public:
+  MockContentControllerDelayed()
+      : mTime(SampleTime::FromTest(GetStartupTime())) {}
+
+  const TimeStamp& Time() { return mTime.Time(); }
+  const SampleTime& GetSampleTime() { return mTime; }
+
+  void AdvanceByMillis(int aMillis) {
+    AdvanceBy(TimeDuration::FromMilliseconds(aMillis));
+  }
+
+  void AdvanceBy(const TimeDuration& aIncrement) {
+    SampleTime target = mTime + aIncrement;
+    while (mTaskQueue.Length() > 0 && mTaskQueue[0].second <= target) {
+      RunNextDelayedTask();
+    }
+    mTime = target;
+  }
+
+  void PostDelayedTask(already_AddRefed<Runnable> aTask, int aDelayMs) {
+    RefPtr<Runnable> task = aTask;
+    SampleTime runAtTime = mTime + TimeDuration::FromMilliseconds(aDelayMs);
+    int insIndex = mTaskQueue.Length();
+    while (insIndex > 0) {
+      if (mTaskQueue[insIndex - 1].second <= runAtTime) {
+        break;
+      }
+      insIndex--;
+    }
+    mTaskQueue.InsertElementAt(insIndex, std::make_pair(task, runAtTime));
+  }
+
+  // Run all the tasks in the queue, returning the number of tasks
+  // run. Note that if a task queues another task while running, that
+  // new task will not be run. Therefore, there may be still be tasks
+  // in the queue after this function is called. Only when the return
+  // value is 0 is the queue guaranteed to be empty.
+  int RunThroughDelayedTasks() {
+    nsTArray<std::pair<RefPtr<Runnable>, SampleTime>> runQueue =
+        std::move(mTaskQueue);
+    int numTasks = runQueue.Length();
+    for (int i = 0; i < numTasks; i++) {
+      mTime = runQueue[i].second;
+      runQueue[i].first->Run();
+
+      // Deleting the task is important in order to release the reference to
+      // the callee object.
+      runQueue[i].first = nullptr;
+    }
+    return numTasks;
+  }
+
+ private:
+  void RunNextDelayedTask() {
+    std::pair<RefPtr<Runnable>, SampleTime> next = mTaskQueue[0];
+    mTaskQueue.RemoveElementAt(0);
+    mTime = next.second;
+    next.first->Run();
+    // Deleting the task is important in order to release the reference to
+    // the callee object.
+    next.first = nullptr;
+  }
+
+  // The following array is sorted by timestamp (tasks are inserted in order by
+  // timestamp).
+  nsTArray<std::pair<RefPtr<Runnable>, SampleTime>> mTaskQueue;
+  SampleTime mTime;
+};
+
+class TestAPZCTreeManager : public APZCTreeManager {
+ public:
+  explicit TestAPZCTreeManager(MockContentControllerDelayed* aMcc,
+                               UniquePtr<IAPZHitTester> aHitTester = nullptr)
+      : APZCTreeManager(LayersId{0}, std::move(aHitTester)), mcc(aMcc) {}
+
+  RefPtr<InputQueue> GetInputQueue() const { return mInputQueue; }
+
+  void ClearContentController() { mcc = nullptr; }
+
+  /**
+   * This function is not currently implemented.
+   * See bug 1468804 for more information.
+   **/
+  void CancelAnimation() { EXPECT_TRUE(false); }
+
+  APZEventResult ReceiveInputEvent(
+      InputData& aEvent,
+      InputBlockCallback&& aCallback = InputBlockCallback()) override {
+    APZEventResult result =
+        APZCTreeManager::ReceiveInputEvent(aEvent, std::move(aCallback));
+    if (aEvent.mInputType == PANGESTURE_INPUT &&
+        // In the APZCTreeManager::ReceiveInputEvent some type of pan gesture
+        // events are marked as `mHandledByAPZ = false` (e.g. with Ctrl key
+        // modifier which causes reflow zoom), in such cases the events will
+        // never be processed by InputQueue so we shouldn't try to invoke
+        // AllowsSwipe() here.
+        aEvent.AsPanGestureInput().mHandledByAPZ &&
+        aEvent.AsPanGestureInput().AllowsSwipe()) {
+      SetBrowserGestureResponse(result.mInputBlockId,
+                                BrowserGestureResponse::NotConsumed);
+    }
+    return result;
+  }
+
+ protected:
+  AsyncPanZoomController* NewAPZCInstance(
+      LayersId aLayersId, GeckoContentController* aController) override;
+
+  SampleTime GetFrameTime() override { return mcc->GetSampleTime(); }
+
+ private:
+  RefPtr<MockContentControllerDelayed> mcc;
+};
+
+class TestAsyncPanZoomController : public AsyncPanZoomController {
+ public:
+  TestAsyncPanZoomController(LayersId aLayersId,
+                             MockContentControllerDelayed* aMcc,
+                             TestAPZCTreeManager* aTreeManager,
+                             GestureBehavior aBehavior = DEFAULT_GESTURES)
+      : AsyncPanZoomController(aLayersId, aTreeManager,
+                               aTreeManager->GetInputQueue(), aMcc, aBehavior),
+        mWaitForMainThread(false),
+        mcc(aMcc) {}
+
+  APZEventResult ReceiveInputEvent(
+      InputData& aEvent,
+      const Maybe<nsTArray<uint32_t>>& aTouchBehaviors = Nothing()) {
+    // This is a function whose signature matches exactly the ReceiveInputEvent
+    // on APZCTreeManager. This allows us to templates for functions like
+    // TouchDown, TouchUp, etc so that we can reuse the code for dispatching
+    // events into both APZC and APZCTM.
+    APZEventResult result = GetInputQueue()->ReceiveInputEvent(
+        this, TargetConfirmationFlags{!mWaitForMainThread}, aEvent,
+        aTouchBehaviors);
+
+    if (aEvent.mInputType == PANGESTURE_INPUT &&
+        aEvent.AsPanGestureInput().AllowsSwipe()) {
+      GetInputQueue()->SetBrowserGestureResponse(
+          result.mInputBlockId, BrowserGestureResponse::NotConsumed);
+    }
+    return result;
+  }
+
+  void ContentReceivedInputBlock(uint64_t aInputBlockId, bool aPreventDefault) {
+    GetInputQueue()->ContentReceivedInputBlock(aInputBlockId, aPreventDefault);
+  }
+
+  void ConfirmTarget(uint64_t aInputBlockId) {
+    RefPtr<AsyncPanZoomController> target = this;
+    GetInputQueue()->SetConfirmedTargetApzc(aInputBlockId, target);
+  }
+
+  void SetAllowedTouchBehavior(uint64_t aInputBlockId,
+                               const nsTArray<TouchBehaviorFlags>& aBehaviors) {
+    GetInputQueue()->SetAllowedTouchBehavior(aInputBlockId, aBehaviors);
+  }
+
+  void SetFrameMetrics(const FrameMetrics& metrics) {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    Metrics() = metrics;
+  }
+
+  void SetScrollMetadata(const ScrollMetadata& aMetadata) {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    mScrollMetadata = aMetadata;
+  }
+
+  FrameMetrics& GetFrameMetrics() {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    return mScrollMetadata.GetMetrics();
+  }
+
+  ScrollMetadata& GetScrollMetadata() {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    return mScrollMetadata;
+  }
+
+  const FrameMetrics& GetFrameMetrics() const {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    return mScrollMetadata.GetMetrics();
+  }
+
+  using AsyncPanZoomController::GetOverscrollAmount;
+  using AsyncPanZoomController::GetVelocityVector;
+
+  void AssertStateIsReset() const {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(NOTHING, mState);
+  }
+
+  void AssertStateIsFling() const {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(FLING, mState);
+  }
+
+  void AssertStateIsSmoothScroll() const {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(SMOOTH_SCROLL, mState);
+  }
+
+  void AssertStateIsSmoothMsdScroll() const {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(SMOOTHMSD_SCROLL, mState);
+  }
+
+  void AssertStateIsPanningLockedY() {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(PANNING_LOCKED_Y, mState);
+  }
+
+  void AssertStateIsPanningLockedX() {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(PANNING_LOCKED_X, mState);
+  }
+
+  void AssertStateIsPanning() {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(PANNING, mState);
+  }
+
+  void AssertStateIsPanMomentum() {
+    RecursiveMutexAutoLock lock(mRecursiveMutex);
+    EXPECT_EQ(PAN_MOMENTUM, mState);
+  }
+
+  void SetAxisLocked(ScrollDirections aDirections, bool aLockValue) {
+    if (aDirections.contains(ScrollDirection::eVertical)) {
+      mY.SetAxisLocked(aLockValue);
+    }
+    if (aDirections.contains(ScrollDirection::eHorizontal)) {
+      mX.SetAxisLocked(aLockValue);
+    }
+  }
+
+  void AssertNotAxisLocked() const {
+    EXPECT_FALSE(mY.IsAxisLocked());
+    EXPECT_FALSE(mX.IsAxisLocked());
+  }
+
+  void AssertAxisLocked(ScrollDirection aDirection) const {
+    switch (aDirection) {
+      case ScrollDirection::eHorizontal:
+        EXPECT_TRUE(mY.IsAxisLocked());
+        EXPECT_FALSE(mX.IsAxisLocked());
+        break;
+      case ScrollDirection::eVertical:
+        EXPECT_TRUE(mX.IsAxisLocked());
+        EXPECT_FALSE(mY.IsAxisLocked());
+        break;
+      default:
+        FAIL() << "input direction must be either vertical or horizontal";
+    }
+  }
+
+  void AdvanceAnimationsUntilEnd(
+      const TimeDuration& aIncrement = TimeDuration::FromMilliseconds(10)) {
+    while (AdvanceAnimations(mcc->GetSampleTime())) {
+      mcc->AdvanceBy(aIncrement);
+    }
+  }
+
+  bool SampleContentTransformForFrame(
+      AsyncTransform* aOutTransform, ParentLayerPoint& aScrollOffset,
+      const TimeDuration& aIncrement = TimeDuration::FromMilliseconds(0)) {
+    mcc->AdvanceBy(aIncrement);
+    bool ret = AdvanceAnimations(mcc->GetSampleTime());
+    if (aOutTransform) {
+      *aOutTransform =
+          GetCurrentAsyncTransform(AsyncPanZoomController::eForHitTesting);
+    }
+    aScrollOffset =
+        GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+    return ret;
+  }
+
+  CSSPoint GetCompositedScrollOffset() const {
+    return GetCurrentAsyncScrollOffset(
+               AsyncPanZoomController::eForCompositing) /
+           GetFrameMetrics().GetZoom();
+  }
+
+  void SetWaitForMainThread() { mWaitForMainThread = true; }
+
+  bool IsOverscrollAnimationRunning() const {
+    return mState == PanZoomState::OVERSCROLL_ANIMATION;
+  }
+
+ private:
+  bool mWaitForMainThread;
+  MockContentControllerDelayed* mcc;
+};
+
+class APZCTesterBase : public ::testing::Test {
+ public:
+  APZCTesterBase() { mcc = new NiceMock<MockContentControllerDelayed>(); }
+
+  void SetUp() override {
+    gfxPlatform::GetPlatform();
+    // This pref is changed in Pan() without using SCOPED_GFX_PREF
+    // because the modified value needs to be in place until the touch
+    // events are processed, which may not happen until the input queue
+    // is flushed in TearDown(). So, we save and restore its value here.
+    mTouchStartTolerance = StaticPrefs::apz_touch_start_tolerance();
+  }
+
+  void TearDown() override {
+    Preferences::SetFloat("apz.touch_start_tolerance", mTouchStartTolerance);
+  }
+
+  enum class PanOptions {
+    None = 0,
+    KeepFingerDown = 0x1,
+    /*
+     * Do not adjust the touch-start coordinates to overcome the touch-start
+     * tolerance threshold. If this option is passed, it's up to the caller
+     * to pass in coordinates that are sufficient to overcome the touch-start
+     * tolerance *and* cause the desired amount of scrolling.
+     */
+    ExactCoordinates = 0x2,
+    NoFling = 0x4
+  };
+
+  enum class PinchOptions {
+    None = 0,
+    LiftFinger1 = 0x1,
+    LiftFinger2 = 0x2,
+    /*
+     * The bitwise OR result of (LiftFinger1 | LiftFinger2).
+     * Defined explicitly here because it is used as the default
+     * argument for PinchWithTouchInput which is defined BEFORE the
+     * definition of operator| for this class.
+     */
+    LiftBothFingers = 0x3
+  };
+
+  template <class InputReceiver>
+  APZEventResult Tap(const RefPtr<InputReceiver>& aTarget,
+                     const ScreenIntPoint& aPoint, TimeDuration aTapLength,
+                     nsEventStatus (*aOutEventStatuses)[2] = nullptr,
+                     uint64_t* aOutInputBlockId = nullptr);
+
+  template <class InputReceiver>
+  void TapAndCheckStatus(const RefPtr<InputReceiver>& aTarget,
+                         const ScreenIntPoint& aPoint, TimeDuration aTapLength);
+
+  template <class InputReceiver>
+  void Pan(const RefPtr<InputReceiver>& aTarget,
+           const ScreenIntPoint& aTouchStart, const ScreenIntPoint& aTouchEnd,
+           PanOptions aOptions = PanOptions::None,
+           nsTArray<uint32_t>* aAllowedTouchBehaviors = nullptr,
+           nsEventStatus (*aOutEventStatuses)[4] = nullptr,
+           uint64_t* aOutInputBlockId = nullptr);
+
+  /*
+   * A version of Pan() that only takes y coordinates rather than (x, y) points
+   * for the touch start and end points, and uses 10 for the x coordinates.
+   * This is for convenience, as most tests only need to pan in one direction.
+   */
+  template <class InputReceiver>
+  void Pan(const RefPtr<InputReceiver>& aTarget, int aTouchStartY,
+           int aTouchEndY, PanOptions aOptions = PanOptions::None,
+           nsTArray<uint32_t>* aAllowedTouchBehaviors = nullptr,
+           nsEventStatus (*aOutEventStatuses)[4] = nullptr,
+           uint64_t* aOutInputBlockId = nullptr);
+
+  /*
+   * Dispatches mock touch events to the apzc and checks whether apzc properly
+   * consumed them and triggered scrolling behavior.
+   */
+  template <class InputReceiver>
+  void PanAndCheckStatus(const RefPtr<InputReceiver>& aTarget, int aTouchStartY,
+                         int aTouchEndY, bool aExpectConsumed,
+                         nsTArray<uint32_t>* aAllowedTouchBehaviors,
+                         uint64_t* aOutInputBlockId = nullptr);
+
+  template <class InputReceiver>
+  void DoubleTap(const RefPtr<InputReceiver>& aTarget,
+                 const ScreenIntPoint& aPoint,
+                 nsEventStatus (*aOutEventStatuses)[4] = nullptr,
+                 uint64_t (*aOutInputBlockIds)[2] = nullptr);
+
+  template <class InputReceiver>
+  void DoubleTapAndCheckStatus(const RefPtr<InputReceiver>& aTarget,
+                               const ScreenIntPoint& aPoint,
+                               uint64_t (*aOutInputBlockIds)[2] = nullptr);
+
+  template <class InputReceiver>
+  void PinchWithTouchInput(
+      const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+      const ScreenIntPoint& aSecondFocus, float aScale, int& inputId,
+      nsTArray<uint32_t>* aAllowedTouchBehaviors = nullptr,
+      nsEventStatus (*aOutEventStatuses)[4] = nullptr,
+      uint64_t* aOutInputBlockId = nullptr,
+      PinchOptions aOptions = PinchOptions::LiftBothFingers,
+      bool aVertical = false);
+
+  // Pinch with one focus point. Zooms in place with no panning
+  template <class InputReceiver>
+  void PinchWithTouchInput(
+      const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+      float aScale, int& inputId,
+      nsTArray<uint32_t>* aAllowedTouchBehaviors = nullptr,
+      nsEventStatus (*aOutEventStatuses)[4] = nullptr,
+      uint64_t* aOutInputBlockId = nullptr,
+      PinchOptions aOptions = PinchOptions::LiftBothFingers,
+      bool aVertical = false);
+
+  template <class InputReceiver>
+  void PinchWithTouchInputAndCheckStatus(
+      const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+      float aScale, int& inputId, bool aShouldTriggerPinch,
+      nsTArray<uint32_t>* aAllowedTouchBehaviors);
+
+  template <class InputReceiver>
+  void PinchWithPinchInput(const RefPtr<InputReceiver>& aTarget,
+                           const ScreenIntPoint& aFocus,
+                           const ScreenIntPoint& aSecondFocus, float aScale,
+                           nsEventStatus (*aOutEventStatuses)[3] = nullptr);
+
+  template <class InputReceiver>
+  void PinchWithPinchInputAndCheckStatus(const RefPtr<InputReceiver>& aTarget,
+                                         const ScreenIntPoint& aFocus,
+                                         float aScale,
+                                         bool aShouldTriggerPinch);
+
+ protected:
+  RefPtr<MockContentControllerDelayed> mcc;
+
+ private:
+  float mTouchStartTolerance;
+};
+
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(APZCTesterBase::PanOptions)
+MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(APZCTesterBase::PinchOptions)
+
+template <class InputReceiver>
+APZEventResult APZCTesterBase::Tap(const RefPtr<InputReceiver>& aTarget,
+                                   const ScreenIntPoint& aPoint,
+                                   TimeDuration aTapLength,
+                                   nsEventStatus (*aOutEventStatuses)[2],
+                                   uint64_t* aOutInputBlockId) {
+  APZEventResult touchDownResult = TouchDown(aTarget, aPoint, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[0] = touchDownResult.GetStatus();
+  }
+  if (aOutInputBlockId) {
+    *aOutInputBlockId = touchDownResult.mInputBlockId;
+  }
+  mcc->AdvanceBy(aTapLength);
+
+  // If touch-action is enabled then simulate the allowed touch behaviour
+  // notification that the main thread is supposed to deliver.
+  if (touchDownResult.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(aTarget, touchDownResult.mInputBlockId);
+  }
+
+  APZEventResult touchUpResult = TouchUp(aTarget, aPoint, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[1] = touchUpResult.GetStatus();
+  }
+  return touchDownResult;
+}
+
+template <class InputReceiver>
+void APZCTesterBase::TapAndCheckStatus(const RefPtr<InputReceiver>& aTarget,
+                                       const ScreenIntPoint& aPoint,
+                                       TimeDuration aTapLength) {
+  nsEventStatus statuses[2];
+  Tap(aTarget, aPoint, aTapLength, &statuses);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[0]);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[1]);
+}
+
+template <class InputReceiver>
+void APZCTesterBase::Pan(const RefPtr<InputReceiver>& aTarget,
+                         const ScreenIntPoint& aTouchStart,
+                         const ScreenIntPoint& aTouchEnd, PanOptions aOptions,
+                         nsTArray<uint32_t>* aAllowedTouchBehaviors,
+                         nsEventStatus (*aOutEventStatuses)[4],
+                         uint64_t* aOutInputBlockId) {
+  // Reduce the move tolerance to a tiny value.
+  // We can't use a scoped pref because this value might be read at some later
+  // time when the events are actually processed, rather than when we deliver
+  // them.
+  const float touchStartTolerance = 0.1f;
+  const float panThreshold = touchStartTolerance * aTarget->GetDPI();
+  Preferences::SetFloat("apz.touch_start_tolerance", touchStartTolerance);
+  Preferences::SetFloat("apz.touch_move_tolerance", 0.0f);
+  int overcomeTouchToleranceX = 0;
+  int overcomeTouchToleranceY = 0;
+  if (!(aOptions & PanOptions::ExactCoordinates)) {
+    // Have the direction of the adjustment to overcome the touch tolerance
+    // match the direction of the entire gesture, otherwise we run into
+    // trouble such as accidentally activating the axis lock.
+    if (aTouchStart.x != aTouchEnd.x && aTouchStart.y != aTouchEnd.y) {
+      // Tests that need to avoid rounding error here can arrange for
+      // panThreshold to be 10 (by setting the DPI to 100), which makes sure
+      // that these are the legs in a Pythagorean triple where panThreshold is
+      // the hypotenuse. Watch out for changes of APZCPinchTester::mDPI.
+      overcomeTouchToleranceX = panThreshold / 10 * 6;
+      overcomeTouchToleranceY = panThreshold / 10 * 8;
+    } else if (aTouchStart.x != aTouchEnd.x) {
+      overcomeTouchToleranceX = panThreshold;
+    } else if (aTouchStart.y != aTouchEnd.y) {
+      overcomeTouchToleranceY = panThreshold;
+    }
+  }
+
+  const TimeDuration TIME_BETWEEN_TOUCH_EVENT =
+      TimeDuration::FromMilliseconds(20);
+
+  // Even if the caller doesn't care about the block id, we need it to set the
+  // allowed touch behaviour below, so make sure aOutInputBlockId is non-null.
+  uint64_t blockId;
+  if (!aOutInputBlockId) {
+    aOutInputBlockId = &blockId;
+  }
+
+  // Make sure the move is large enough to not be handled as a tap
+  APZEventResult result =
+      TouchDown(aTarget,
+                ScreenIntPoint(aTouchStart.x + overcomeTouchToleranceX,
+                               aTouchStart.y + overcomeTouchToleranceY),
+                mcc->Time());
+  if (aOutInputBlockId) {
+    *aOutInputBlockId = result.mInputBlockId;
+  }
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[0] = result.GetStatus();
+  }
+
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // Allowed touch behaviours must be set after sending touch-start.
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    if (aAllowedTouchBehaviors) {
+      EXPECT_EQ(1UL, aAllowedTouchBehaviors->Length());
+      aTarget->SetAllowedTouchBehavior(*aOutInputBlockId,
+                                       *aAllowedTouchBehaviors);
+    } else {
+      SetDefaultAllowedTouchBehavior(aTarget, *aOutInputBlockId);
+    }
+  }
+
+  result = TouchMove(aTarget, aTouchStart, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[1] = result.GetStatus();
+  }
+
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  const int numSteps = 3;
+  auto stepVector = (aTouchEnd - aTouchStart) / numSteps;
+  for (int k = 1; k < numSteps; k++) {
+    auto stepPoint = aTouchStart + stepVector * k;
+    Unused << TouchMove(aTarget, stepPoint, mcc->Time());
+
+    mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+  }
+
+  result = TouchMove(aTarget, aTouchEnd, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[2] = result.GetStatus();
+  }
+
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  if (!(aOptions & PanOptions::KeepFingerDown)) {
+    result = TouchUp(aTarget, aTouchEnd, mcc->Time());
+  } else {
+    result.SetStatusAsIgnore();
+  }
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[3] = result.GetStatus();
+  }
+
+  if ((aOptions & PanOptions::NoFling)) {
+    aTarget->CancelAnimation();
+  }
+
+  // Don't increment the time here. Animations started on touch-up, such as
+  // flings, are affected by elapsed time, and we want to be able to sample
+  // them immediately after they start, without time having elapsed.
+}
+
+template <class InputReceiver>
+void APZCTesterBase::Pan(const RefPtr<InputReceiver>& aTarget, int aTouchStartY,
+                         int aTouchEndY, PanOptions aOptions,
+                         nsTArray<uint32_t>* aAllowedTouchBehaviors,
+                         nsEventStatus (*aOutEventStatuses)[4],
+                         uint64_t* aOutInputBlockId) {
+  Pan(aTarget, ScreenIntPoint(10, aTouchStartY), ScreenIntPoint(10, aTouchEndY),
+      aOptions, aAllowedTouchBehaviors, aOutEventStatuses, aOutInputBlockId);
+}
+
+template <class InputReceiver>
+void APZCTesterBase::PanAndCheckStatus(
+    const RefPtr<InputReceiver>& aTarget, int aTouchStartY, int aTouchEndY,
+    bool aExpectConsumed, nsTArray<uint32_t>* aAllowedTouchBehaviors,
+    uint64_t* aOutInputBlockId) {
+  nsEventStatus statuses[4];  // down, move, move, up
+  Pan(aTarget, aTouchStartY, aTouchEndY, PanOptions::None,
+      aAllowedTouchBehaviors, &statuses, aOutInputBlockId);
+
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[0]);
+
+  nsEventStatus touchMoveStatus;
+  if (aExpectConsumed) {
+    touchMoveStatus = nsEventStatus_eConsumeDoDefault;
+  } else {
+    touchMoveStatus = nsEventStatus_eIgnore;
+  }
+  EXPECT_EQ(touchMoveStatus, statuses[1]);
+  EXPECT_EQ(touchMoveStatus, statuses[2]);
+}
+
+template <class InputReceiver>
+void APZCTesterBase::DoubleTap(const RefPtr<InputReceiver>& aTarget,
+                               const ScreenIntPoint& aPoint,
+                               nsEventStatus (*aOutEventStatuses)[4],
+                               uint64_t (*aOutInputBlockIds)[2]) {
+  APZEventResult result = TouchDown(aTarget, aPoint, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[0] = result.GetStatus();
+  }
+  if (aOutInputBlockIds) {
+    (*aOutInputBlockIds)[0] = result.mInputBlockId;
+  }
+  mcc->AdvanceByMillis(10);
+
+  // If touch-action is enabled then simulate the allowed touch behaviour
+  // notification that the main thread is supposed to deliver.
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(aTarget, result.mInputBlockId);
+  }
+
+  result = TouchUp(aTarget, aPoint, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[1] = result.GetStatus();
+  }
+  mcc->AdvanceByMillis(10);
+  result = TouchDown(aTarget, aPoint, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[2] = result.GetStatus();
+  }
+  if (aOutInputBlockIds) {
+    (*aOutInputBlockIds)[1] = result.mInputBlockId;
+  }
+  mcc->AdvanceByMillis(10);
+
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(aTarget, result.mInputBlockId);
+  }
+
+  result = TouchUp(aTarget, aPoint, mcc->Time());
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[3] = result.GetStatus();
+  }
+}
+
+template <class InputReceiver>
+void APZCTesterBase::DoubleTapAndCheckStatus(
+    const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aPoint,
+    uint64_t (*aOutInputBlockIds)[2]) {
+  nsEventStatus statuses[4];
+  DoubleTap(aTarget, aPoint, &statuses, aOutInputBlockIds);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[0]);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[1]);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[2]);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[3]);
+}
+
+template <class InputReceiver>
+void APZCTesterBase::PinchWithTouchInput(
+    const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+    float aScale, int& inputId, nsTArray<uint32_t>* aAllowedTouchBehaviors,
+    nsEventStatus (*aOutEventStatuses)[4], uint64_t* aOutInputBlockId,
+    PinchOptions aOptions, bool aVertical) {
+  // Perform a pinch gesture with the same start & end focus point
+  PinchWithTouchInput(aTarget, aFocus, aFocus, aScale, inputId,
+                      aAllowedTouchBehaviors, aOutEventStatuses,
+                      aOutInputBlockId, aOptions, aVertical);
+}
+
+template <class InputReceiver>
+void APZCTesterBase::PinchWithTouchInput(
+    const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+    const ScreenIntPoint& aSecondFocus, float aScale, int& inputId,
+    nsTArray<uint32_t>* aAllowedTouchBehaviors,
+    nsEventStatus (*aOutEventStatuses)[4], uint64_t* aOutInputBlockId,
+    PinchOptions aOptions, bool aVertical) {
+  // Having pinch coordinates in float type may cause problems with
+  // high-precision scale values since SingleTouchData accepts integer value.
+  // But for trivial tests it should be ok.
+  const float pinchLength = 100.0;
+  const float pinchLengthScaled = pinchLength * aScale;
+
+  const float pinchLengthX = aVertical ? 0 : pinchLength;
+  const float pinchLengthScaledX = aVertical ? 0 : pinchLengthScaled;
+  const float pinchLengthY = aVertical ? pinchLength : 0;
+  const float pinchLengthScaledY = aVertical ? pinchLengthScaled : 0;
+
+  // Even if the caller doesn't care about the block id, we need it to set the
+  // allowed touch behaviour below, so make sure aOutInputBlockId is non-null.
+  uint64_t blockId;
+  if (!aOutInputBlockId) {
+    aOutInputBlockId = &blockId;
+  }
+
+  const TimeDuration TIME_BETWEEN_TOUCH_EVENT =
+      TimeDuration::FromMilliseconds(20);
+
+  MultiTouchInput mtiStart =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_START, 0, mcc->Time(), 0);
+  mtiStart.mTouches.AppendElement(CreateSingleTouchData(inputId, aFocus));
+  mtiStart.mTouches.AppendElement(CreateSingleTouchData(inputId + 1, aFocus));
+  APZEventResult result;
+  result = aTarget->ReceiveInputEvent(mtiStart);
+  if (aOutInputBlockId) {
+    *aOutInputBlockId = result.mInputBlockId;
+  }
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[0] = result.GetStatus();
+  }
+
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  if (aAllowedTouchBehaviors) {
+    EXPECT_EQ(2UL, aAllowedTouchBehaviors->Length());
+    aTarget->SetAllowedTouchBehavior(*aOutInputBlockId,
+                                     *aAllowedTouchBehaviors);
+  } else {
+    SetDefaultAllowedTouchBehavior(aTarget, *aOutInputBlockId, 2);
+  }
+
+  ScreenIntPoint pinchStartPoint1(aFocus.x - int32_t(pinchLengthX),
+                                  aFocus.y - int32_t(pinchLengthY));
+  ScreenIntPoint pinchStartPoint2(aFocus.x + int32_t(pinchLengthX),
+                                  aFocus.y + int32_t(pinchLengthY));
+
+  MultiTouchInput mtiMove1 =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mtiMove1.mTouches.AppendElement(
+      CreateSingleTouchData(inputId, pinchStartPoint1));
+  mtiMove1.mTouches.AppendElement(
+      CreateSingleTouchData(inputId + 1, pinchStartPoint2));
+  result = aTarget->ReceiveInputEvent(mtiMove1);
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[1] = result.GetStatus();
+  }
+
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // Pinch instantly but move in steps.
+  const int numSteps = 3;
+  auto stepVector = (aSecondFocus - aFocus) / numSteps;
+  for (int k = 1; k < numSteps; k++) {
+    ScreenIntPoint stepFocus = aFocus + stepVector * k;
+    ScreenIntPoint stepPoint1(stepFocus.x - int32_t(pinchLengthScaledX),
+                              stepFocus.y - int32_t(pinchLengthScaledY));
+    ScreenIntPoint stepPoint2(stepFocus.x + int32_t(pinchLengthScaledX),
+                              stepFocus.y + int32_t(pinchLengthScaledY));
+    MultiTouchInput mtiMoveStep =
+        MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+    mtiMoveStep.mTouches.AppendElement(
+        CreateSingleTouchData(inputId, stepPoint1));
+    mtiMoveStep.mTouches.AppendElement(
+        CreateSingleTouchData(inputId + 1, stepPoint2));
+    Unused << aTarget->ReceiveInputEvent(mtiMoveStep);
+
+    mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+  }
+
+  ScreenIntPoint pinchEndPoint1(aSecondFocus.x - int32_t(pinchLengthScaledX),
+                                aSecondFocus.y - int32_t(pinchLengthScaledY));
+  ScreenIntPoint pinchEndPoint2(aSecondFocus.x + int32_t(pinchLengthScaledX),
+                                aSecondFocus.y + int32_t(pinchLengthScaledY));
+
+  MultiTouchInput mtiMove2 =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mtiMove2.mTouches.AppendElement(
+      CreateSingleTouchData(inputId, pinchEndPoint1));
+  mtiMove2.mTouches.AppendElement(
+      CreateSingleTouchData(inputId + 1, pinchEndPoint2));
+  result = aTarget->ReceiveInputEvent(mtiMove2);
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[2] = result.GetStatus();
+  }
+
+  if (aOptions & (PinchOptions::LiftFinger1 | PinchOptions::LiftFinger2)) {
+    mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+    MultiTouchInput mtiEnd =
+        MultiTouchInput(MultiTouchInput::MULTITOUCH_END, 0, mcc->Time(), 0);
+    if (aOptions & PinchOptions::LiftFinger1) {
+      mtiEnd.mTouches.AppendElement(
+          CreateSingleTouchData(inputId, pinchEndPoint1));
+    }
+    if (aOptions & PinchOptions::LiftFinger2) {
+      mtiEnd.mTouches.AppendElement(
+          CreateSingleTouchData(inputId + 1, pinchEndPoint2));
+    }
+    result = aTarget->ReceiveInputEvent(mtiEnd);
+    if (aOutEventStatuses) {
+      (*aOutEventStatuses)[3] = result.GetStatus();
+    }
+  }
+
+  inputId += 2;
+}
+
+template <class InputReceiver>
+void APZCTesterBase::PinchWithTouchInputAndCheckStatus(
+    const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+    float aScale, int& inputId, bool aShouldTriggerPinch,
+    nsTArray<uint32_t>* aAllowedTouchBehaviors) {
+  nsEventStatus statuses[4];  // down, move, move, up
+  PinchWithTouchInput(aTarget, aFocus, aScale, inputId, aAllowedTouchBehaviors,
+                      &statuses);
+
+  nsEventStatus expectedMoveStatus = aShouldTriggerPinch
+                                         ? nsEventStatus_eConsumeDoDefault
+                                         : nsEventStatus_eIgnore;
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault, statuses[0]);
+  EXPECT_EQ(expectedMoveStatus, statuses[1]);
+  EXPECT_EQ(expectedMoveStatus, statuses[2]);
+}
+
+template <class InputReceiver>
+void APZCTesterBase::PinchWithPinchInput(
+    const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+    const ScreenIntPoint& aSecondFocus, float aScale,
+    nsEventStatus (*aOutEventStatuses)[3]) {
+  const TimeDuration TIME_BETWEEN_PINCH_INPUT =
+      TimeDuration::FromMilliseconds(50);
+
+  auto event = CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_START,
+                                       aFocus, 10.0, 10.0, mcc->Time());
+  APZEventResult actual = aTarget->ReceiveInputEvent(event);
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[0] = actual.GetStatus();
+  }
+  mcc->AdvanceBy(TIME_BETWEEN_PINCH_INPUT);
+
+  event =
+      CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_SCALE,
+                              aSecondFocus, 10.0 * aScale, 10.0, mcc->Time());
+  actual = aTarget->ReceiveInputEvent(event);
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[1] = actual.GetStatus();
+  }
+  mcc->AdvanceBy(TIME_BETWEEN_PINCH_INPUT);
+
+  event =
+      CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_END, aSecondFocus,
+                              10.0 * aScale, 10.0 * aScale, mcc->Time());
+  actual = aTarget->ReceiveInputEvent(event);
+  if (aOutEventStatuses) {
+    (*aOutEventStatuses)[2] = actual.GetStatus();
+  }
+}
+
+template <class InputReceiver>
+void APZCTesterBase::PinchWithPinchInputAndCheckStatus(
+    const RefPtr<InputReceiver>& aTarget, const ScreenIntPoint& aFocus,
+    float aScale, bool aShouldTriggerPinch) {
+  nsEventStatus statuses[3];  // scalebegin, scale, scaleend
+  PinchWithPinchInput(aTarget, aFocus, aFocus, aScale, &statuses);
+
+  nsEventStatus expectedStatus = aShouldTriggerPinch
+                                     ? nsEventStatus_eConsumeDoDefault
+                                     : nsEventStatus_eIgnore;
+  EXPECT_EQ(expectedStatus, statuses[0]);
+  EXPECT_EQ(expectedStatus, statuses[1]);
+}
+
+inline FrameMetrics TestFrameMetrics() {
+  FrameMetrics fm;
+
+  fm.SetDisplayPort(CSSRect(0, 0, 10, 10));
+  fm.SetCompositionBounds(ParentLayerRect(0, 0, 10, 10));
+  fm.SetScrollableRect(CSSRect(0, 0, 100, 100));
+
+  return fm;
+}
+
+#endif  // mozilla_layers_APZTestCommon_h
diff --git a/gfx/layers/apz/test/gtest/InputUtils.h b/gfx/layers/apz/test/gtest/InputUtils.h
new file mode 100644
index 0000000000..a654369a61
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/InputUtils.h
@@ -0,0 +1,149 @@
+/* -*- 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_InputUtils_h
+#define mozilla_layers_InputUtils_h
+
+/**
+ * Defines a set of utility functions for generating input events
+ * to an APZC/APZCTM during APZ gtests.
+ */
+
+#include "APZTestCommon.h"
+
+/* The InputReceiver template parameter used in the helper functions below needs
+ * to be a class that implements functions with the signatures:
+ * APZEventResult ReceiveInputEvent(const InputData& aEvent);
+ * void SetAllowedTouchBehavior(uint64_t aInputBlockId,
+ *                              const nsTArray<uint32_t>& aBehaviours);
+ * The classes that currently implement these are APZCTreeManager and
+ * TestAsyncPanZoomController. Using this template allows us to test individual
+ * APZC instances in isolation and also an entire APZ tree, while using the same
+ * code to dispatch input events.
+ */
+
+template <class InputReceiver>
+void SetDefaultAllowedTouchBehavior(const RefPtr<InputReceiver>& aTarget,
+                                    uint64_t aInputBlockId,
+                                    int touchPoints = 1) {
+  nsTArray<uint32_t> defaultBehaviors;
+  // use the default value where everything is allowed
+  for (int i = 0; i < touchPoints; i++) {
+    defaultBehaviors.AppendElement(
+        mozilla::layers::AllowedTouchBehavior::HORIZONTAL_PAN |
+        mozilla::layers::AllowedTouchBehavior::VERTICAL_PAN |
+        mozilla::layers::AllowedTouchBehavior::PINCH_ZOOM |
+        mozilla::layers::AllowedTouchBehavior::DOUBLE_TAP_ZOOM);
+  }
+  aTarget->SetAllowedTouchBehavior(aInputBlockId, defaultBehaviors);
+}
+
+inline MultiTouchInput CreateMultiTouchInput(
+    MultiTouchInput::MultiTouchType aType, TimeStamp aTime) {
+  return MultiTouchInput(aType, MillisecondsSinceStartup(aTime), aTime, 0);
+}
+
+template <class InputReceiver>
+APZEventResult TouchDown(const RefPtr<InputReceiver>& aTarget,
+                         const ScreenIntPoint& aPoint, TimeStamp aTime) {
+  MultiTouchInput mti =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, aTime);
+  mti.mTouches.AppendElement(CreateSingleTouchData(0, aPoint));
+  return aTarget->ReceiveInputEvent(mti);
+}
+
+template <class InputReceiver>
+APZEventResult TouchMove(const RefPtr<InputReceiver>& aTarget,
+                         const ScreenIntPoint& aPoint, TimeStamp aTime) {
+  MultiTouchInput mti =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, aTime);
+  mti.mTouches.AppendElement(CreateSingleTouchData(0, aPoint));
+  return aTarget->ReceiveInputEvent(mti);
+}
+
+template <class InputReceiver>
+APZEventResult TouchUp(const RefPtr<InputReceiver>& aTarget,
+                       const ScreenIntPoint& aPoint, TimeStamp aTime) {
+  MultiTouchInput mti =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_END, aTime);
+  mti.mTouches.AppendElement(CreateSingleTouchData(0, aPoint));
+  return aTarget->ReceiveInputEvent(mti);
+}
+
+template <class InputReceiver>
+APZEventResult Wheel(const RefPtr<InputReceiver>& aTarget,
+                     const ScreenIntPoint& aPoint, const ScreenPoint& aDelta,
+                     TimeStamp aTime) {
+  ScrollWheelInput input(aTime, 0, ScrollWheelInput::SCROLLMODE_INSTANT,
+                         ScrollWheelInput::SCROLLDELTA_PIXEL, aPoint, aDelta.x,
+                         aDelta.y, false, WheelDeltaAdjustmentStrategy::eNone);
+  return aTarget->ReceiveInputEvent(input);
+}
+
+template <class InputReceiver>
+APZEventResult SmoothWheel(const RefPtr<InputReceiver>& aTarget,
+                           const ScreenIntPoint& aPoint,
+                           const ScreenPoint& aDelta, TimeStamp aTime) {
+  ScrollWheelInput input(aTime, 0, ScrollWheelInput::SCROLLMODE_SMOOTH,
+                         ScrollWheelInput::SCROLLDELTA_LINE, aPoint, aDelta.x,
+                         aDelta.y, false, WheelDeltaAdjustmentStrategy::eNone);
+  return aTarget->ReceiveInputEvent(input);
+}
+
+template <class InputReceiver>
+APZEventResult MouseDown(const RefPtr<InputReceiver>& aTarget,
+                         const ScreenIntPoint& aPoint, TimeStamp aTime) {
+  MouseInput input(MouseInput::MOUSE_DOWN,
+                   MouseInput::ButtonType::PRIMARY_BUTTON, 0, 0, aPoint, aTime,
+                   0);
+  return aTarget->ReceiveInputEvent(input);
+}
+
+template <class InputReceiver>
+APZEventResult MouseMove(const RefPtr<InputReceiver>& aTarget,
+                         const ScreenIntPoint& aPoint, TimeStamp aTime) {
+  MouseInput input(MouseInput::MOUSE_MOVE,
+                   MouseInput::ButtonType::PRIMARY_BUTTON, 0, 0, aPoint, aTime,
+                   0);
+  return aTarget->ReceiveInputEvent(input);
+}
+
+template <class InputReceiver>
+APZEventResult MouseUp(const RefPtr<InputReceiver>& aTarget,
+                       const ScreenIntPoint& aPoint, TimeStamp aTime) {
+  MouseInput input(MouseInput::MOUSE_UP, MouseInput::ButtonType::PRIMARY_BUTTON,
+                   0, 0, aPoint, aTime, 0);
+  return aTarget->ReceiveInputEvent(input);
+}
+
+template <class InputReceiver>
+APZEventResult PanGesture(PanGestureInput::PanGestureType aType,
+                          const RefPtr<InputReceiver>& aTarget,
+                          const ScreenIntPoint& aPoint,
+                          const ScreenPoint& aDelta, TimeStamp aTime,
+                          Modifiers aModifiers = MODIFIER_NONE,
+                          bool aSimulateMomentum = false) {
+  PanGestureInput input(aType, aTime, aPoint, aDelta, aModifiers);
+  input.mSimulateMomentum = aSimulateMomentum;
+  if constexpr (std::is_same_v<InputReceiver, TestAsyncPanZoomController>) {
+    // In the case of TestAsyncPanZoomController we know for sure that the
+    // event will be handled by APZ so set it explicitly.
+    input.mHandledByAPZ = true;
+  }
+  return aTarget->ReceiveInputEvent(input);
+}
+
+template <class InputReceiver>
+APZEventResult PanGestureWithModifiers(PanGestureInput::PanGestureType aType,
+                                       Modifiers aModifiers,
+                                       const RefPtr<InputReceiver>& aTarget,
+                                       const ScreenIntPoint& aPoint,
+                                       const ScreenPoint& aDelta,
+                                       TimeStamp aTime) {
+  return PanGesture(aType, aTarget, aPoint, aDelta, aTime, aModifiers);
+}
+
+#endif  // mozilla_layers_InputUtils_h
diff --git a/gfx/layers/apz/test/gtest/MockHitTester.cpp b/gfx/layers/apz/test/gtest/MockHitTester.cpp
new file mode 100644
index 0000000000..025866ca65
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/MockHitTester.cpp
@@ -0,0 +1,38 @@
+/* -*- 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 "MockHitTester.h"
+#include "apz/src/AsyncPanZoomController.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+
+namespace mozilla::layers {
+
+IAPZHitTester::HitTestResult MockHitTester::GetAPZCAtPoint(
+    const ScreenPoint& aHitTestPoint,
+    const RecursiveMutexAutoLock& aProofOfTreeLock) {
+  MOZ_ASSERT(!mQueuedResults.empty());
+  HitTestResult result = std::move(mQueuedResults.front());
+  mQueuedResults.pop();
+  return result;
+}
+
+void MockHitTester::QueueHitResult(ScrollableLayerGuid::ViewID aScrollId,
+                                   gfx::CompositorHitTestInfo aHitInfo) {
+  LayersId layersId = GetRootLayersId();  // currently this is all the tests use
+  RefPtr<HitTestingTreeNode> node =
+      GetTargetNode(ScrollableLayerGuid(layersId, 0, aScrollId),
+                    ScrollableLayerGuid::EqualsIgnoringPresShell);
+  MOZ_ASSERT(node);
+  AsyncPanZoomController* apzc = node->GetApzc();
+  MOZ_ASSERT(apzc);
+  HitTestResult result;
+  result.mTargetApzc = apzc;
+  result.mHitResult = aHitInfo;
+  result.mLayersId = layersId;
+  mQueuedResults.push(std::move(result));
+}
+
+}  // namespace mozilla::layers
diff --git a/gfx/layers/apz/test/gtest/MockHitTester.h b/gfx/layers/apz/test/gtest/MockHitTester.h
new file mode 100644
index 0000000000..9c91b31152
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/MockHitTester.h
@@ -0,0 +1,37 @@
+/* -*- 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_MockHitTester_h
+#define mozilla_layers_MockHitTester_h
+
+#include "apz/src/IAPZHitTester.h"
+#include "mozilla/gfx/CompositorHitTestInfo.h"
+
+#include <queue>
+
+namespace mozilla::layers {
+
+// IAPZHitTester implementation for APZ gtests.
+// This does not actually perform hit-testing, it just allows
+// the test code to specify the expected hit test results.
+class MockHitTester final : public IAPZHitTester {
+ public:
+  HitTestResult GetAPZCAtPoint(
+      const ScreenPoint& aHitTestPoint,
+      const RecursiveMutexAutoLock& aProofOfTreeLock) override;
+
+  // Queue a hit test result whose target APZC is the APZC
+  // with scroll id |aScrollId|, and the provided hit test flags.
+  void QueueHitResult(ScrollableLayerGuid::ViewID aScrollId,
+                      gfx::CompositorHitTestInfo aHitInfo);
+
+ private:
+  std::queue<HitTestResult> mQueuedResults;
+};
+
+}  // namespace mozilla::layers
+
+#endif  // define mozilla_layers_MockHitTester_h
diff --git a/gfx/layers/apz/test/gtest/TestAxisLock.cpp b/gfx/layers/apz/test/gtest/TestAxisLock.cpp
new file mode 100644
index 0000000000..8b0df3e8a2
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestAxisLock.cpp
@@ -0,0 +1,645 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+
+#include "InputUtils.h"
+#include "gtest/gtest.h"
+
+#include <cmath>
+
+class APZCAxisLockCompatTester : public APZCTreeManagerTester,
+                                 public testing::WithParamInterface<int> {
+ public:
+  APZCAxisLockCompatTester() : oldAxisLockMode(0) { CreateMockHitTester(); }
+
+  int oldAxisLockMode;
+
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+
+  RefPtr<TestAsyncPanZoomController> apzc;
+
+  void SetUp() {
+    APZCTreeManagerTester::SetUp();
+
+    oldAxisLockMode = Preferences::GetInt("apz.axis_lock.mode");
+
+    Preferences::SetInt("apz.axis_lock.mode", GetParam());
+  }
+
+  void TearDown() {
+    APZCTreeManagerTester::TearDown();
+
+    Preferences::SetInt("apz.axis_lock.mode", oldAxisLockMode);
+  }
+
+  static std::string PrintFromParam(const testing::TestParamInfo<int>& info) {
+    switch (info.param) {
+      case 0:
+        return "FREE";
+      case 1:
+        return "STANDARD";
+      case 2:
+        return "STICKY";
+      case 3:
+        return "DOMINANT_AXIS";
+      default:
+        return "UNKNOWN";
+    }
+  }
+};
+
+class APZCAxisLockTester : public APZCTreeManagerTester {
+ public:
+  APZCAxisLockTester() { CreateMockHitTester(); }
+
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+
+  RefPtr<TestAsyncPanZoomController> apzc;
+
+  void SetupBasicTest() {
+    const char* treeShape = "x";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 100, 100),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 500, 500));
+
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+
+    UpdateHitTestingTree();
+  }
+
+  void BreakStickyAxisLockTestGesture(const ScrollDirections& aDirections) {
+    float panX = 0;
+    float panY = 0;
+
+    if (aDirections.contains(ScrollDirection::eVertical)) {
+      panY = 30;
+    }
+    if (aDirections.contains(ScrollDirection::eHorizontal)) {
+      panX = 30;
+    }
+
+    // Kick off the gesture that may lock onto an axis
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+    PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+               ScreenPoint(panX, panY), mcc->Time());
+    mcc->AdvanceByMillis(5);
+    apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+    PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+               ScreenPoint(panX, panY), mcc->Time());
+  }
+
+  void BreakStickyAxisLockTest(const ScrollDirections& aDirections) {
+    // Create the gesture for the test.
+    BreakStickyAxisLockTestGesture(aDirections);
+
+    // Based on the scroll direction(s) ensure the state is what we expect.
+    if (aDirections == ScrollDirection::eVertical) {
+      apzc->AssertStateIsPanningLockedY();
+      apzc->AssertAxisLocked(ScrollDirection::eVertical);
+      EXPECT_GT(apzc->GetVelocityVector().y, 0);
+      EXPECT_EQ(apzc->GetVelocityVector().x, 0);
+    } else if (aDirections == ScrollDirection::eHorizontal) {
+      apzc->AssertStateIsPanningLockedX();
+      apzc->AssertAxisLocked(ScrollDirection::eHorizontal);
+      EXPECT_GT(apzc->GetVelocityVector().x, 0);
+      EXPECT_EQ(apzc->GetVelocityVector().y, 0);
+    } else {
+      apzc->AssertStateIsPanning();
+      apzc->AssertNotAxisLocked();
+      EXPECT_GT(apzc->GetVelocityVector().x, 0);
+      EXPECT_GT(apzc->GetVelocityVector().y, 0);
+    }
+
+    // Cleanup for next test.
+    apzc->AdvanceAnimationsUntilEnd();
+  }
+};
+
+TEST_F(APZCAxisLockTester, BasicDominantAxisUse) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 1);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.lock_angle", M_PI / 4.0f);
+
+  SetupBasicTest();
+
+  apzc = ApzcOf(root);
+
+  // Kick off the initial gesture that triggers the momentum scroll.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+
+  // Should be in a PANNING_LOCKED_Y state with no horizontal velocity.
+  apzc->AssertStateIsPanningLockedY();
+  apzc->AssertAxisLocked(ScrollDirection::eVertical);
+  EXPECT_GT(apzc->GetVelocityVector().y, 0);
+  EXPECT_EQ(apzc->GetVelocityVector().x, 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Ensure that we have not panned on the horizontal axis.
+  ParentLayerPoint panEndOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+  EXPECT_EQ(panEndOffset.x, 0);
+
+  // The lock onto the Y axis extends into momentum scroll.
+  apzc->AssertAxisLocked(ScrollDirection::eVertical);
+
+  // Start the momentum scroll.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(30, 90), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(10, 30), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(10, 30), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // In momentum locking mode, we should still be locked onto the Y axis.
+  apzc->AssertStateIsPanMomentum();
+  apzc->AssertAxisLocked(ScrollDirection::eVertical);
+  EXPECT_GT(apzc->GetVelocityVector().y, 0);
+  EXPECT_EQ(apzc->GetVelocityVector().x, 0);
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(0, 0), mcc->Time());
+
+  // After momentum scroll end, ensure we are no longer locked onto an axis.
+  apzc->AssertNotAxisLocked();
+
+  // Wait until the end of the animation and ensure the final state is
+  // reasonable.
+  apzc->AdvanceAnimationsUntilEnd();
+  ParentLayerPoint finalOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+
+  // Ensure we have scrolled some amount on the Y axis in momentum scroll.
+  EXPECT_GT(finalOffset.y, panEndOffset.y);
+  EXPECT_EQ(finalOffset.x, 0.0f);
+}
+
+TEST_F(APZCAxisLockTester, NewGestureBreaksMomentumAxisLock) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 1);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.lock_angle", M_PI / 4.0f);
+
+  SetupBasicTest();
+
+  apzc = ApzcOf(root);
+
+  // Kick off the initial gesture that triggers the momentum scroll.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(2, 1), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(30, 15), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(30, 15), mcc->Time());
+
+  // Should be in a PANNING_LOCKED_X state with no vertical velocity.
+  apzc->AssertStateIsPanningLockedX();
+  apzc->AssertAxisLocked(ScrollDirection::eHorizontal);
+  EXPECT_GT(apzc->GetVelocityVector().x, 0);
+  EXPECT_EQ(apzc->GetVelocityVector().y, 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Double check that we have not panned on the vertical axis.
+  ParentLayerPoint panEndOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+  EXPECT_EQ(panEndOffset.y, 0);
+
+  // Ensure that the axis locks extends into momentum scroll.
+  apzc->AssertAxisLocked(ScrollDirection::eHorizontal);
+
+  // Start the momentum scroll.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(80, 40), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(20, 10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(20, 10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // In momentum locking mode, we should still be locked onto the X axis.
+  apzc->AssertStateIsPanMomentum();
+  apzc->AssertAxisLocked(ScrollDirection::eHorizontal);
+  EXPECT_GT(apzc->GetVelocityVector().x, 0);
+  EXPECT_EQ(apzc->GetVelocityVector().y, 0);
+
+  ParentLayerPoint beforeBreakOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+  EXPECT_EQ(beforeBreakOffset.y, 0);
+  // Ensure we have scrolled some amount on the X axis in momentum scroll.
+  EXPECT_GT(beforeBreakOffset.x, panEndOffset.x);
+
+  // Kick off the gesture that breaks the lock onto the X axis.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  ParentLayerPoint afterBreakOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+
+  // The lock onto the X axis should be broken and we now should be locked
+  // onto the Y axis.
+  apzc->AssertStateIsPanningLockedY();
+  apzc->AssertAxisLocked(ScrollDirection::eVertical);
+  EXPECT_GT(apzc->GetVelocityVector().y, 0);
+  EXPECT_EQ(apzc->GetVelocityVector().x, 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // The lock onto the Y axis extends into momentum scroll.
+  apzc->AssertAxisLocked(ScrollDirection::eVertical);
+
+  // Wait until the end of the animation and ensure the final state is
+  // reasonable.
+  apzc->AdvanceAnimationsUntilEnd();
+  ParentLayerPoint finalOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+
+  EXPECT_GT(finalOffset.y, 0);
+  // Ensure that we did not scroll on the X axis after the vertical scroll
+  // started.
+  EXPECT_EQ(finalOffset.x, afterBreakOffset.x);
+}
+
+TEST_F(APZCAxisLockTester, BreakStickyAxisLock) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 2);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.lock_angle", M_PI / 6.0f);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.breakout_angle", M_PI / 6.0f);
+
+  SetupBasicTest();
+
+  apzc = ApzcOf(root);
+
+  // Start a gesture to get us locked onto the Y axis.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Ensure that we have locked onto the Y axis.
+  apzc->AssertStateIsPanningLockedY();
+
+  // Test switch to locking onto the X axis.
+  BreakStickyAxisLockTest(ScrollDirection::eHorizontal);
+
+  // Test switch back to locking onto the Y axis.
+  BreakStickyAxisLockTest(ScrollDirection::eVertical);
+
+  // Test breaking all axis locks from a Y axis lock.
+  BreakStickyAxisLockTest(ScrollDirections(ScrollDirection::eHorizontal,
+                                           ScrollDirection::eVertical));
+
+  // We should be in a panning state.
+  apzc->AssertStateIsPanning();
+  apzc->AssertNotAxisLocked();
+
+  // Lock back to the X axis.
+  BreakStickyAxisLockTestGesture(ScrollDirection::eHorizontal);
+
+  // End the gesture.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Start a gesture to get us locked onto the X axis.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(2, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Ensure that we have locked onto the X axis.
+  apzc->AssertStateIsPanningLockedX();
+
+  // Test breaking all axis locks from a X axis lock.
+  BreakStickyAxisLockTest(ScrollDirections(ScrollDirection::eHorizontal,
+                                           ScrollDirection::eVertical));
+
+  // We should be in a panning state.
+  apzc->AssertStateIsPanning();
+  apzc->AssertNotAxisLocked();
+
+  // Test switch back to locking onto the Y axis.
+  BreakStickyAxisLockTest(ScrollDirection::eVertical);
+}
+
+TEST_F(APZCAxisLockTester, BreakAxisLockByLockAngle) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 2);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.lock_angle", M_PI / 4.0f);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.breakout_angle", M_PI / 8.0f);
+
+  SetupBasicTest();
+
+  apzc = ApzcOf(root);
+
+  // Start a gesture to get us locked onto the Y axis.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Ensure that we have locked onto the Y axis.
+  apzc->AssertStateIsPanningLockedY();
+
+  // Stay within 45 degrees from the X axis, and more than 22.5 degrees from
+  // the Y axis. This should break the Y lock and lock us to the X axis.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(12, 10), mcc->Time());
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Ensure that we have locked onto the X axis.
+  apzc->AssertStateIsPanningLockedX();
+
+  // End the gesture.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+}
+
+TEST_F(APZCAxisLockTester, TestDominantAxisScrolling) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 3);
+
+  int panY;
+  int panX;
+
+  SetupBasicTest();
+
+  apzc = ApzcOf(root);
+
+  ParentLayerPoint lastOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+
+  // In dominant axis mode, test pan gesture events with varying gesture
+  // angles and ensure that we only pan on one axis.
+  for (panX = 0, panY = 50; panY >= 0; panY -= 10, panX += 5) {
+    // Gesture that should be locked onto one axis
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+    PanGesture(PanGestureInput::PANGESTURE_START, manager,
+               ScreenIntPoint(50, 50), ScreenIntPoint(panX, panY), mcc->Time());
+    mcc->AdvanceByMillis(5);
+    apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+    PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+               ScreenPoint(static_cast<float>(panX), static_cast<float>(panY)),
+               mcc->Time());
+    mcc->AdvanceByMillis(5);
+    apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+    PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+               ScreenPoint(0, 0), mcc->Time());
+    apzc->AdvanceAnimationsUntilEnd();
+
+    ParentLayerPoint scrollOffset = apzc->GetCurrentAsyncScrollOffset(
+        AsyncPanZoomController::eForHitTesting);
+
+    if (panX > panY) {
+      // If we're closer to the X axis ensure that we moved on the horizontal
+      // axis and there was no movement on the vertical axis.
+      EXPECT_GT(scrollOffset.x, lastOffset.x);
+      EXPECT_EQ(scrollOffset.y, lastOffset.y);
+    } else {
+      // If we're closer to the Y axis ensure that we moved on the vertical
+      // axis and there was no movement on the horizontal axis.
+      EXPECT_GT(scrollOffset.y, lastOffset.y);
+      EXPECT_EQ(scrollOffset.x, lastOffset.x);
+    }
+
+    lastOffset = scrollOffset;
+  }
+}
+
+TEST_F(APZCAxisLockTester, TestCanScrollWithAxisLock) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 2);
+
+  SetupBasicTest();
+
+  apzc = ApzcOf(root);
+
+  // The axis locks do not impact CanScroll()
+  apzc->SetAxisLocked(ScrollDirection::eHorizontal, true);
+  EXPECT_EQ(apzc->CanScroll(ParentLayerPoint(10, 0)), true);
+
+  apzc->SetAxisLocked(ScrollDirection::eHorizontal, false);
+  apzc->SetAxisLocked(ScrollDirection::eVertical, true);
+  EXPECT_EQ(apzc->CanScroll(ParentLayerPoint(0, 10)), true);
+}
+
+TEST_F(APZCAxisLockTester, TestScrollHandoffAxisLockConflict) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 2);
+
+  // Create two scrollable frames. One parent frame with one child.
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {
+      LayerIntRect(0, 0, 100, 100),
+      LayerIntRect(0, 0, 100, 100),
+  };
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 500, 500));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            CSSRect(0, 0, 500, 500));
+  SetScrollHandoff(layers[1], root);
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+
+  UpdateHitTestingTree();
+
+  RefPtr<TestAsyncPanZoomController> rootApzc = ApzcOf(root);
+  apzc = ApzcOf(layers[1]);
+
+  // Create a gesture on the y-axis that should lock the x axis.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 15), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimationsUntilEnd();
+
+  // We are locked onto the y-axis.
+  apzc->AssertAxisLocked(ScrollDirection::eVertical);
+
+  // There should be movement in the child.
+  ParentLayerPoint childCurrentOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+  EXPECT_GT(childCurrentOffset.y, 0);
+  EXPECT_EQ(childCurrentOffset.x, 0);
+
+  // There should be no movement in the parent.
+  ParentLayerPoint parentCurrentOffset = rootApzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+  EXPECT_EQ(parentCurrentOffset.y, 0);
+  EXPECT_EQ(parentCurrentOffset.x, 0);
+
+  // Create a gesture on the x-axis, that should be directed
+  // at the child, even if the x-axis is locked.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(2, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimationsUntilEnd();
+
+  // We broke the y-axis lock and are now locked onto the x-axis.
+  apzc->AssertAxisLocked(ScrollDirection::eHorizontal);
+
+  // There should be some movement in the child on the x-axis.
+  ParentLayerPoint childFinalOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+  EXPECT_GT(childFinalOffset.x, 0);
+
+  // There should still be no movement in the parent.
+  ParentLayerPoint parentFinalOffset = rootApzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+  EXPECT_EQ(parentFinalOffset.y, 0);
+  EXPECT_EQ(parentFinalOffset.x, 0);
+}
+
+// The delta from the initial pan gesture should be reflected in the
+// current offset for all axis locking modes.
+TEST_P(APZCAxisLockCompatTester, TestPanGestureStart) {
+  const char* treeShape = "x";
+  LayerIntRegion layerVisibleRegion[] = {
+      LayerIntRect(0, 0, 100, 100),
+  };
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 500, 500));
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+
+  UpdateHitTestingTree();
+
+  apzc = ApzcOf(root);
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(0, 10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimationsUntilEnd();
+  ParentLayerPoint currentOffset = apzc->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting);
+
+  EXPECT_EQ(currentOffset.x, 0);
+  EXPECT_EQ(currentOffset.y, 10);
+}
+
+// All APZCAxisLockCompatTester tests should be run for each apz.axis_lock.mode.
+// If another mode is added, the value should be added to this list.
+INSTANTIATE_TEST_SUITE_P(APZCAxisLockCompat, APZCAxisLockCompatTester,
+                         testing::Values(0, 1, 2, 3),
+                         APZCAxisLockCompatTester::PrintFromParam);
diff --git a/gfx/layers/apz/test/gtest/TestBasic.cpp b/gfx/layers/apz/test/gtest/TestBasic.cpp
new file mode 100644
index 0000000000..ccce43a0de
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestBasic.cpp
@@ -0,0 +1,636 @@
+/* -*- 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 "APZCBasicTester.h"
+#include "APZTestCommon.h"
+
+#include "InputUtils.h"
+
+static ScrollGenerationCounter sGenerationCounter;
+
+TEST_F(APZCBasicTester, Overzoom) {
+  // the visible area of the document in CSS pixels is x=10 y=0 w=100 h=100
+  FrameMetrics fm;
+  fm.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  fm.SetScrollableRect(CSSRect(0, 0, 125, 150));
+  fm.SetVisualScrollOffset(CSSPoint(10, 0));
+  fm.SetZoom(CSSToParentLayerScale(1.0));
+  fm.SetIsRootContent(true);
+  apzc->SetFrameMetrics(fm);
+
+  MakeApzcZoomable();
+
+  EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(1);
+
+  PinchWithPinchInputAndCheckStatus(apzc, ScreenIntPoint(50, 50), 0.5, true);
+
+  fm = apzc->GetFrameMetrics();
+  EXPECT_EQ(0.8f, fm.GetZoom().scale);
+  // bug 936721 - PGO builds introduce rounding error so
+  // use a fuzzy match instead
+  EXPECT_LT(std::abs(fm.GetVisualScrollOffset().x), 1e-5);
+  EXPECT_LT(std::abs(fm.GetVisualScrollOffset().y), 1e-5);
+}
+
+TEST_F(APZCBasicTester, ZoomLimits) {
+  SCOPED_GFX_PREF_FLOAT("apz.min_zoom", 0.9f);
+  SCOPED_GFX_PREF_FLOAT("apz.max_zoom", 2.0f);
+
+  // the visible area of the document in CSS pixels is x=10 y=0 w=100 h=100
+  FrameMetrics fm;
+  fm.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  fm.SetScrollableRect(CSSRect(0, 0, 125, 150));
+  fm.SetZoom(CSSToParentLayerScale(1.0));
+  fm.SetIsRootContent(true);
+  apzc->SetFrameMetrics(fm);
+
+  MakeApzcZoomable();
+
+  // This should take the zoom scale to 0.8, but we've capped it at 0.9.
+  PinchWithPinchInputAndCheckStatus(apzc, ScreenIntPoint(50, 50), 0.5, true);
+
+  fm = apzc->GetFrameMetrics();
+  EXPECT_EQ(0.9f, fm.GetZoom().scale);
+
+  // This should take the zoom scale to 2.7, but we've capped it at 2.
+  PinchWithPinchInputAndCheckStatus(apzc, ScreenIntPoint(50, 50), 3, true);
+
+  fm = apzc->GetFrameMetrics();
+  EXPECT_EQ(2.0f, fm.GetZoom().scale);
+}
+
+TEST_F(APZCBasicTester, SimpleTransform) {
+  ParentLayerPoint pointOut;
+  AsyncTransform viewTransformOut;
+  apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+
+  EXPECT_EQ(ParentLayerPoint(), pointOut);
+  EXPECT_EQ(AsyncTransform(), viewTransformOut);
+}
+
+TEST_F(APZCBasicTester, ComplexTransform) {
+  // This test assumes there is a page that gets rendered to
+  // two layers. In CSS pixels, the first layer is 50x50 and
+  // the second layer is 25x50. The widget scale factor is 3.0
+  // and the presShell resolution is 2.0. Therefore, these layers
+  // end up being 300x300 and 150x300 in layer pixels.
+  //
+  // The second (child) layer has an additional CSS transform that
+  // stretches it by 2.0 on the x-axis. Therefore, after applying
+  // CSS transforms, the two layers are the same size in screen
+  // pixels.
+  //
+  // The screen itself is 24x24 in screen pixels (therefore 4x4 in
+  // CSS pixels). The displayport is 1 extra CSS pixel on all
+  // sides.
+
+  RefPtr<TestAsyncPanZoomController> childApzc =
+      new TestAsyncPanZoomController(LayersId{0}, mcc, tm);
+
+  const char* treeShape = "x(x)";
+  // LayerID                     0 1
+  LayerIntRegion layerVisibleRegion[] = {
+      LayerIntRect(0, 0, 300, 300),
+      LayerIntRect(0, 0, 150, 300),
+  };
+  Matrix4x4 transforms[] = {
+      Matrix4x4(),
+      Matrix4x4(),
+  };
+  transforms[0].PostScale(
+      0.5f, 0.5f,
+      1.0f);  // this results from the 2.0 resolution on the root layer
+  transforms[1].PostScale(
+      2.0f, 1.0f,
+      1.0f);  // this is the 2.0 x-axis CSS transform on the child layer
+
+  auto layers = TestWRScrollData::Create(treeShape, *updater,
+                                         layerVisibleRegion, transforms);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 24, 24));
+  metrics.SetDisplayPort(CSSRect(-1, -1, 6, 6));
+  metrics.SetVisualScrollOffset(CSSPoint(10, 10));
+  metrics.SetLayoutViewport(CSSRect(10, 10, 8, 8));
+  metrics.SetScrollableRect(CSSRect(0, 0, 50, 50));
+  metrics.SetCumulativeResolution(LayoutDeviceToLayerScale(2));
+  metrics.SetPresShellResolution(2.0f);
+  metrics.SetZoom(CSSToParentLayerScale(6));
+  metrics.SetDevPixelsPerCSSPixel(CSSToLayoutDeviceScale(3));
+  metrics.SetScrollId(ScrollableLayerGuid::START_SCROLL_ID);
+
+  ScrollMetadata childMetadata = metadata;
+  FrameMetrics& childMetrics = childMetadata.GetMetrics();
+  childMetrics.SetScrollId(ScrollableLayerGuid::START_SCROLL_ID + 1);
+
+  layers[0]->AppendScrollMetadata(layers, metadata);
+  layers[1]->AppendScrollMetadata(layers, childMetadata);
+
+  ParentLayerPoint pointOut;
+  AsyncTransform viewTransformOut;
+
+  // Both the parent and child layer should behave exactly the same here,
+  // because the CSS transform on the child layer does not affect the
+  // SampleContentTransformForFrame code
+
+  // initial transform
+  apzc->SetFrameMetrics(metrics);
+  apzc->NotifyLayersUpdated(metadata, true, true);
+  apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  EXPECT_EQ(AsyncTransform(LayerToParentLayerScale(1), ParentLayerPoint()),
+            viewTransformOut);
+  EXPECT_EQ(ParentLayerPoint(60, 60), pointOut);
+
+  childApzc->SetFrameMetrics(childMetrics);
+  childApzc->NotifyLayersUpdated(childMetadata, true, true);
+  childApzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  EXPECT_EQ(AsyncTransform(LayerToParentLayerScale(1), ParentLayerPoint()),
+            viewTransformOut);
+  EXPECT_EQ(ParentLayerPoint(60, 60), pointOut);
+
+  // do an async scroll by 5 pixels and check the transform
+  metrics.ScrollBy(CSSPoint(5, 0));
+  apzc->SetFrameMetrics(metrics);
+  apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  EXPECT_EQ(
+      AsyncTransform(LayerToParentLayerScale(1), ParentLayerPoint(-30, 0)),
+      viewTransformOut);
+  EXPECT_EQ(ParentLayerPoint(90, 60), pointOut);
+
+  childMetrics.ScrollBy(CSSPoint(5, 0));
+  childApzc->SetFrameMetrics(childMetrics);
+  childApzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  EXPECT_EQ(
+      AsyncTransform(LayerToParentLayerScale(1), ParentLayerPoint(-30, 0)),
+      viewTransformOut);
+  EXPECT_EQ(ParentLayerPoint(90, 60), pointOut);
+
+  // do an async zoom of 1.5x and check the transform
+  metrics.ZoomBy(1.5f);
+  apzc->SetFrameMetrics(metrics);
+  apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  EXPECT_EQ(
+      AsyncTransform(LayerToParentLayerScale(1.5), ParentLayerPoint(-45, 0)),
+      viewTransformOut);
+  EXPECT_EQ(ParentLayerPoint(135, 90), pointOut);
+
+  childMetrics.ZoomBy(1.5f);
+  childApzc->SetFrameMetrics(childMetrics);
+  childApzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+  EXPECT_EQ(
+      AsyncTransform(LayerToParentLayerScale(1.5), ParentLayerPoint(-45, 0)),
+      viewTransformOut);
+  EXPECT_EQ(ParentLayerPoint(135, 90), pointOut);
+
+  childApzc->Destroy();
+}
+
+TEST_F(APZCBasicTester, Fling) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+  int touchStart = 50;
+  int touchEnd = 10;
+  ParentLayerPoint pointOut;
+  AsyncTransform viewTransformOut;
+
+  // Fling down. Each step scroll further down
+  Pan(apzc, touchStart, touchEnd);
+  ParentLayerPoint lastPoint;
+  for (int i = 1; i < 50; i += 1) {
+    apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut,
+                                         TimeDuration::FromMilliseconds(1));
+    EXPECT_GT(pointOut.y, lastPoint.y);
+    lastPoint = pointOut;
+  }
+}
+
+#ifndef MOZ_WIDGET_ANDROID  // Maybe fails on Android
+TEST_F(APZCBasicTester, ResumeInterruptedTouchDrag_Bug1592435) {
+  // Start a touch-drag and scroll some amount, not lifting the finger.
+  SCOPED_GFX_PREF_FLOAT("apz.touch_start_tolerance", 1.0f / 1000.0f);
+  ScreenIntPoint touchPos(10, 50);
+  uint64_t touchBlock = TouchDown(apzc, touchPos, mcc->Time()).mInputBlockId;
+  SetDefaultAllowedTouchBehavior(apzc, touchBlock);
+  for (int i = 0; i < 20; ++i) {
+    touchPos.y -= 1;
+    mcc->AdvanceByMillis(1);
+    TouchMove(apzc, touchPos, mcc->Time());
+  }
+
+  // Take note of the scroll offset before the interruption.
+  CSSPoint scrollOffsetBeforeInterruption =
+      apzc->GetFrameMetrics().GetVisualScrollOffset();
+
+  // Have the main thread interrupt the touch-drag by sending
+  // a main thread scroll update to a nearby location.
+  CSSPoint mainThreadOffset = scrollOffsetBeforeInterruption;
+  mainThreadOffset.y -= 5;
+  ScrollMetadata metadata = apzc->GetScrollMetadata();
+  metadata.GetMetrics().SetLayoutScrollOffset(mainThreadOffset);
+  nsTArray<ScrollPositionUpdate> scrollUpdates;
+  scrollUpdates.AppendElement(ScrollPositionUpdate::NewScroll(
+      ScrollOrigin::Other, CSSPoint::ToAppUnits(mainThreadOffset)));
+  metadata.SetScrollUpdates(scrollUpdates);
+  metadata.GetMetrics().SetScrollGeneration(
+      scrollUpdates.LastElement().GetGeneration());
+  apzc->NotifyLayersUpdated(metadata, false, true);
+
+  // Continue and finish the touch-drag gesture.
+  for (int i = 0; i < 20; ++i) {
+    touchPos.y -= 1;
+    mcc->AdvanceByMillis(1);
+    TouchMove(apzc, touchPos, mcc->Time());
+  }
+
+  // Check that the portion of the touch-drag that occurred after
+  // the interruption caused additional scrolling.
+  CSSPoint finalScrollOffset = apzc->GetFrameMetrics().GetVisualScrollOffset();
+  EXPECT_GT(finalScrollOffset.y, scrollOffsetBeforeInterruption.y);
+
+  // Now do the same thing, but for a visual scroll update.
+  scrollOffsetBeforeInterruption =
+      apzc->GetFrameMetrics().GetVisualScrollOffset();
+  mainThreadOffset = scrollOffsetBeforeInterruption;
+  mainThreadOffset.y -= 5;
+  metadata = apzc->GetScrollMetadata();
+  metadata.GetMetrics().SetVisualDestination(mainThreadOffset);
+  metadata.GetMetrics().SetScrollGeneration(
+      sGenerationCounter.NewMainThreadGeneration());
+  metadata.GetMetrics().SetVisualScrollUpdateType(FrameMetrics::eMainThread);
+  scrollUpdates.Clear();
+  metadata.SetScrollUpdates(scrollUpdates);
+  apzc->NotifyLayersUpdated(metadata, false, true);
+  for (int i = 0; i < 20; ++i) {
+    touchPos.y -= 1;
+    mcc->AdvanceByMillis(1);
+    TouchMove(apzc, touchPos, mcc->Time());
+  }
+  finalScrollOffset = apzc->GetFrameMetrics().GetVisualScrollOffset();
+  EXPECT_GT(finalScrollOffset.y, scrollOffsetBeforeInterruption.y);
+
+  // Clean up by ending the touch gesture.
+  mcc->AdvanceByMillis(1);
+  TouchUp(apzc, touchPos, mcc->Time());
+}
+#endif
+
+TEST_F(APZCBasicTester, RelativeScrollOffset) {
+  // Set up initial conditions: zoomed in, layout offset at (100, 100),
+  // visual offset at (120, 120); the relative offset is therefore (20, 20).
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetScrollableRect(CSSRect(0, 0, 1000, 1000));
+  metrics.SetLayoutViewport(CSSRect(100, 100, 100, 100));
+  metrics.SetZoom(CSSToParentLayerScale(2.0));
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetVisualScrollOffset(CSSPoint(120, 120));
+  metrics.SetIsRootContent(true);
+  apzc->SetFrameMetrics(metrics);
+
+  // Scroll the layout viewport to (200, 200).
+  ScrollMetadata mainThreadMetadata = metadata;
+  FrameMetrics& mainThreadMetrics = mainThreadMetadata.GetMetrics();
+  mainThreadMetrics.SetLayoutScrollOffset(CSSPoint(200, 200));
+  nsTArray<ScrollPositionUpdate> scrollUpdates;
+  scrollUpdates.AppendElement(ScrollPositionUpdate::NewScroll(
+      ScrollOrigin::Other, CSSPoint::ToAppUnits(CSSPoint(200, 200))));
+  mainThreadMetadata.SetScrollUpdates(scrollUpdates);
+  mainThreadMetrics.SetScrollGeneration(
+      scrollUpdates.LastElement().GetGeneration());
+  apzc->NotifyLayersUpdated(mainThreadMetadata, /*isFirstPaint=*/false,
+                            /*thisLayerTreeUpdated=*/true);
+
+  // Check that the relative offset has been preserved.
+  metrics = apzc->GetFrameMetrics();
+  EXPECT_EQ(metrics.GetLayoutScrollOffset(), CSSPoint(200, 200));
+  EXPECT_EQ(metrics.GetVisualScrollOffset(), CSSPoint(220, 220));
+}
+
+TEST_F(APZCBasicTester, MultipleSmoothScrollsSmooth) {
+  // We want to test that if we send multiple smooth scroll requests that we
+  // still smoothly animate, ie that we get non-zero change every frame while
+  // the animation is running.
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 10000));
+  metrics.SetLayoutViewport(CSSRect(0, 0, 100, 100));
+  metrics.SetZoom(CSSToParentLayerScale(1.0));
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetVisualScrollOffset(CSSPoint(0, 0));
+  metrics.SetIsRootContent(true);
+  apzc->SetFrameMetrics(metrics);
+
+  // Structure of this test.
+  //   -send a pure relative smooth scroll request via NotifyLayersUpdated
+  //   -advance animations a few times, check that scroll offset is increasing
+  //    after the first few advances
+  //   -send a pure relative smooth scroll request via NotifyLayersUpdated
+  //   -advance animations a few times, check that scroll offset is increasing
+  //   -send a pure relative smooth scroll request via NotifyLayersUpdated
+  //   -advance animations a few times, check that scroll offset is increasing
+
+  ScrollMetadata metadata2 = metadata;
+  nsTArray<ScrollPositionUpdate> scrollUpdates2;
+  scrollUpdates2.AppendElement(ScrollPositionUpdate::NewPureRelativeScroll(
+      ScrollOrigin::Other, ScrollMode::Smooth,
+      CSSPoint::ToAppUnits(CSSPoint(0, 200))));
+  metadata2.SetScrollUpdates(scrollUpdates2);
+  metadata2.GetMetrics().SetScrollGeneration(
+      scrollUpdates2.LastElement().GetGeneration());
+  apzc->NotifyLayersUpdated(metadata2, /*isFirstPaint=*/false,
+                            /*thisLayerTreeUpdated=*/true);
+
+  // Get the animation going
+  for (uint32_t i = 0; i < 3; i++) {
+    SampleAnimationOneFrame();
+  }
+
+  float offset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForCompositing)
+          .y;
+  ASSERT_GT(offset, 0);
+  float lastOffset = offset;
+
+  for (uint32_t i = 0; i < 2; i++) {
+    for (uint32_t j = 0; j < 3; j++) {
+      SampleAnimationOneFrame();
+      offset = apzc->GetCurrentAsyncScrollOffset(
+                       AsyncPanZoomController::eForCompositing)
+                   .y;
+      ASSERT_GT(offset, lastOffset);
+      lastOffset = offset;
+    }
+
+    ScrollMetadata metadata3 = metadata;
+    nsTArray<ScrollPositionUpdate> scrollUpdates3;
+    scrollUpdates3.AppendElement(ScrollPositionUpdate::NewPureRelativeScroll(
+        ScrollOrigin::Other, ScrollMode::Smooth,
+        CSSPoint::ToAppUnits(CSSPoint(0, 200))));
+    metadata3.SetScrollUpdates(scrollUpdates3);
+    metadata3.GetMetrics().SetScrollGeneration(
+        scrollUpdates3.LastElement().GetGeneration());
+    apzc->NotifyLayersUpdated(metadata3, /*isFirstPaint=*/false,
+                              /*thisLayerTreeUpdated=*/true);
+  }
+
+  for (uint32_t j = 0; j < 7; j++) {
+    SampleAnimationOneFrame();
+    offset = apzc->GetCurrentAsyncScrollOffset(
+                     AsyncPanZoomController::eForCompositing)
+                 .y;
+    ASSERT_GT(offset, lastOffset);
+    lastOffset = offset;
+  }
+}
+
+class APZCSmoothScrollTester : public APZCBasicTester {
+ public:
+  // Test that a smooth scroll animation correctly handles its destination
+  // being updated by a relative scroll delta.
+  void TestSmoothScrollDestinationUpdate() {
+    // Set up scroll frame. Starting scroll position is (0, 0).
+    ScrollMetadata metadata;
+    FrameMetrics& metrics = metadata.GetMetrics();
+    metrics.SetScrollableRect(CSSRect(0, 0, 100, 10000));
+    metrics.SetLayoutViewport(CSSRect(0, 0, 100, 100));
+    metrics.SetZoom(CSSToParentLayerScale(1.0));
+    metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+    metrics.SetVisualScrollOffset(CSSPoint(0, 0));
+    metrics.SetIsRootContent(true);
+    apzc->SetFrameMetrics(metrics);
+
+    // Start smooth scroll via main-thread request.
+    nsTArray<ScrollPositionUpdate> scrollUpdates;
+    scrollUpdates.AppendElement(ScrollPositionUpdate::NewPureRelativeScroll(
+        ScrollOrigin::Other, ScrollMode::Smooth,
+        CSSPoint::ToAppUnits(CSSPoint(0, 1000))));
+    metadata.SetScrollUpdates(scrollUpdates);
+    metrics.SetScrollGeneration(scrollUpdates.LastElement().GetGeneration());
+    apzc->NotifyLayersUpdated(metadata, false, true);
+
+    // Sample the smooth scroll animation until we get past y=500.
+    apzc->AssertStateIsSmoothScroll();
+    float y = 0;
+    while (y < 500) {
+      SampleAnimationOneFrame();
+      y = apzc->GetFrameMetrics().GetVisualScrollOffset().y;
+    }
+
+    // Send a relative scroll of y = -400.
+    scrollUpdates.Clear();
+    scrollUpdates.AppendElement(ScrollPositionUpdate::NewRelativeScroll(
+        CSSPoint::ToAppUnits(CSSPoint(0, 500)),
+        CSSPoint::ToAppUnits(CSSPoint(0, 100))));
+    metadata.SetScrollUpdates(scrollUpdates);
+    metrics.SetScrollGeneration(scrollUpdates.LastElement().GetGeneration());
+    apzc->NotifyLayersUpdated(metadata, false, false);
+
+    // Verify the relative scroll was applied but didn't cancel the animation.
+    float y2 = apzc->GetFrameMetrics().GetVisualScrollOffset().y;
+    ASSERT_EQ(y2, y - 400);
+    apzc->AssertStateIsSmoothScroll();
+
+    // Sample the animation again and check that it respected the relative
+    // scroll.
+    SampleAnimationOneFrame();
+    float y3 = apzc->GetFrameMetrics().GetVisualScrollOffset().y;
+    ASSERT_GT(y3, y2);
+    ASSERT_LT(y3, 500);
+
+    // Continue animation until done and check that it ended up at a correctly
+    // adjusted destination.
+    apzc->AdvanceAnimationsUntilEnd();
+    float y4 = apzc->GetFrameMetrics().GetVisualScrollOffset().y;
+    ASSERT_EQ(y4, 600);  // 1000 (initial destination) - 400 (relative scroll)
+  }
+};
+
+TEST_F(APZCSmoothScrollTester, SmoothScrollDestinationUpdateBezier) {
+  SCOPED_GFX_PREF_BOOL("general.smoothScroll.msdPhysics.enabled", false);
+  TestSmoothScrollDestinationUpdate();
+}
+
+TEST_F(APZCSmoothScrollTester, SmoothScrollDestinationUpdateMsd) {
+  SCOPED_GFX_PREF_BOOL("general.smoothScroll.msdPhysics.enabled", true);
+  TestSmoothScrollDestinationUpdate();
+}
+
+TEST_F(APZCBasicTester, ZoomAndScrollableRectChangeAfterZoomChange) {
+  // We want to check that a small scrollable rect change (which causes us to
+  // reclamp our scroll position, including in the sampled state) does not move
+  // the scroll offset in the sample state based the zoom in the apzc, only
+  // based on the zoom in the sampled state.
+
+  // First we zoom in to the right hand side. Then start zooming out, then send
+  // a scrollable rect change and check that it doesn't change the sampled state
+  // scroll offset.
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  metrics.SetLayoutViewport(CSSRect(0, 0, 100, 100));
+  metrics.SetVisualScrollOffset(CSSPoint(0, 0));
+  metrics.SetZoom(CSSToParentLayerScale(1.0));
+  metrics.SetIsRootContent(true);
+  apzc->SetFrameMetrics(metrics);
+
+  MakeApzcZoomable();
+
+  // Zoom to right side.
+  ZoomTarget zoomTarget{CSSRect(75, 25, 25, 25)};
+  apzc->ZoomToRect(zoomTarget, 0);
+
+  // Run the animation to completion, should take 250ms/16.67ms = 15 frames, but
+  // do extra to make sure.
+  for (uint32_t i = 0; i < 30; i++) {
+    SampleAnimationOneFrame();
+  }
+
+  EXPECT_FALSE(apzc->IsAsyncZooming());
+
+  // Zoom out.
+  ZoomTarget zoomTarget2{CSSRect(0, 0, 100, 100)};
+  apzc->ZoomToRect(zoomTarget2, 0);
+
+  // Run the animation a few times to get it going.
+  for (uint32_t i = 0; i < 2; i++) {
+    SampleAnimationOneFrame();
+  }
+
+  // Check that it is decreasing in scale.
+  float prevScale =
+      apzc->GetCurrentPinchZoomScale(AsyncPanZoomController::eForCompositing)
+          .scale;
+  for (uint32_t i = 0; i < 2; i++) {
+    SampleAnimationOneFrame();
+    float scale =
+        apzc->GetCurrentPinchZoomScale(AsyncPanZoomController::eForCompositing)
+            .scale;
+    ASSERT_GT(prevScale, scale);
+    prevScale = scale;
+  }
+
+  float offset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForCompositing)
+          .x;
+
+  // Change the scrollable rect slightly to trigger a reclamp.
+  ScrollMetadata metadata2 = metadata;
+  metadata2.GetMetrics().SetScrollableRect(CSSRect(0, 0, 100, 1000.2));
+  apzc->NotifyLayersUpdated(metadata2, /*isFirstPaint=*/false,
+                            /*thisLayerTreeUpdated=*/true);
+
+  float newOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForCompositing)
+          .x;
+
+  ASSERT_EQ(newOffset, offset);
+}
+
+TEST_F(APZCBasicTester, ZoomToRectAndCompositionBoundsChange) {
+  // We want to check that content sending a composition bounds change (due to
+  // addition of scrollbars) during a zoom animation does not cause us to take
+  // the out of date content resolution.
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetCompositionBoundsWidthIgnoringScrollbars(ParentLayerCoord{100});
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  metrics.SetLayoutViewport(CSSRect(0, 0, 100, 100));
+  metrics.SetVisualScrollOffset(CSSPoint(0, 0));
+  metrics.SetZoom(CSSToParentLayerScale(1.0));
+  metrics.SetIsRootContent(true);
+  apzc->SetFrameMetrics(metrics);
+
+  MakeApzcZoomable();
+
+  // Start a zoom to a rect.
+  ZoomTarget zoomTarget{CSSRect(25, 25, 25, 25)};
+  apzc->ZoomToRect(zoomTarget, 0);
+
+  // Run the animation a few times to get it going.
+  // Check that it is increasing in scale.
+  float prevScale =
+      apzc->GetCurrentPinchZoomScale(AsyncPanZoomController::eForCompositing)
+          .scale;
+  for (uint32_t i = 0; i < 3; i++) {
+    SampleAnimationOneFrame();
+    float scale =
+        apzc->GetCurrentPinchZoomScale(AsyncPanZoomController::eForCompositing)
+            .scale;
+    ASSERT_GE(scale, prevScale);
+    prevScale = scale;
+  }
+
+  EXPECT_TRUE(apzc->IsAsyncZooming());
+
+  // Simulate the appearance of a scrollbar by reducing the width of
+  // the composition bounds, while keeping
+  // mCompositionBoundsWidthIgnoringScrollbars unchanged.
+  ScrollMetadata metadata2 = metadata;
+  metadata2.GetMetrics().SetCompositionBounds(ParentLayerRect(0, 0, 90, 100));
+  apzc->NotifyLayersUpdated(metadata2, /*isFirstPaint=*/false,
+                            /*thisLayerTreeUpdated=*/true);
+
+  float scale =
+      apzc->GetCurrentPinchZoomScale(AsyncPanZoomController::eForCompositing)
+          .scale;
+
+  ASSERT_EQ(scale, prevScale);
+
+  // Run the rest of the animation to completion, should take 250ms/16.67ms = 15
+  // frames total, but do extra to make sure.
+  for (uint32_t i = 0; i < 30; i++) {
+    SampleAnimationOneFrame();
+    scale =
+        apzc->GetCurrentPinchZoomScale(AsyncPanZoomController::eForCompositing)
+            .scale;
+    ASSERT_GE(scale, prevScale);
+    prevScale = scale;
+  }
+
+  EXPECT_FALSE(apzc->IsAsyncZooming());
+}
+
+TEST_F(APZCBasicTester, StartTolerance) {
+  SCOPED_GFX_PREF_FLOAT("apz.touch_start_tolerance", 10 / tm->GetDPI());
+
+  FrameMetrics fm;
+  fm.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  fm.SetScrollableRect(CSSRect(0, 0, 100, 300));
+  fm.SetVisualScrollOffset(CSSPoint(0, 50));
+  fm.SetIsRootContent(true);
+  apzc->SetFrameMetrics(fm);
+
+  uint64_t touchBlock = TouchDown(apzc, {50, 50}, mcc->Time()).mInputBlockId;
+  SetDefaultAllowedTouchBehavior(apzc, touchBlock);
+
+  CSSPoint initialScrollOffset =
+      apzc->GetFrameMetrics().GetVisualScrollOffset();
+
+  mcc->AdvanceByMillis(1);
+  TouchMove(apzc, {50, 70}, mcc->Time());
+
+  // Expect 10 pixels of scrolling: the distance from (50,50) to (50,70)
+  // minus the 10-pixel touch start tolerance.
+  ASSERT_EQ(initialScrollOffset.y - 10,
+            apzc->GetFrameMetrics().GetVisualScrollOffset().y);
+
+  mcc->AdvanceByMillis(1);
+  TouchMove(apzc, {50, 90}, mcc->Time());
+
+  // Expect 30 pixels of scrolling: the distance from (50,50) to (50,90)
+  // minus the 10-pixel touch start tolerance.
+  ASSERT_EQ(initialScrollOffset.y - 30,
+            apzc->GetFrameMetrics().GetVisualScrollOffset().y);
+
+  // Clean up by ending the touch gesture.
+  mcc->AdvanceByMillis(1);
+  TouchUp(apzc, {50, 90}, mcc->Time());
+}
diff --git a/gfx/layers/apz/test/gtest/TestEventRegions.cpp b/gfx/layers/apz/test/gtest/TestEventRegions.cpp
new file mode 100644
index 0000000000..0b4564b49f
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestEventRegions.cpp
@@ -0,0 +1,199 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+#include "mozilla/layers/LayersTypes.h"
+
+class APZEventRegionsTester : public APZCTreeManagerTester {
+ protected:
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+  TestAsyncPanZoomController* rootApzc;
+
+  void CreateEventRegionsLayerTree1() {
+    const char* treeShape = "x(xx)";
+    LayerIntRegion layerVisibleRegions[] = {
+        LayerIntRect(0, 0, 200, 200),    // root
+        LayerIntRect(0, 0, 100, 200),    // left half
+        LayerIntRect(0, 100, 200, 100),  // bottom half
+    };
+    CreateScrollData(treeShape, layerVisibleRegions);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID);
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1);
+    SetScrollableFrameMetrics(layers[2],
+                              ScrollableLayerGuid::START_SCROLL_ID + 2);
+    SetScrollHandoff(layers[1], root);
+    SetScrollHandoff(layers[2], root);
+
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+    rootApzc = ApzcOf(root);
+  }
+
+  void CreateEventRegionsLayerTree2() {
+    const char* treeShape = "x(x)";
+    LayerIntRegion layerVisibleRegions[] = {
+        LayerIntRect(0, 0, 100, 500),
+        LayerIntRect(0, 150, 100, 100),
+    };
+    CreateScrollData(treeShape, layerVisibleRegions);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID);
+
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+    rootApzc = ApzcOf(root);
+  }
+
+  void CreateBug1117712LayerTree() {
+    const char* treeShape = "x(x(x)x)";
+    // LayerID               0 1 2 3
+    // 0 is the root
+    // 1 is a container layer whose sole purpose to make a non-empty ancestor
+    //   transform for 2, so that 2's screen-to-apzc and apzc-to-gecko
+    //   transforms are different from 3's.
+    // 2 is a small layer that is the actual target
+    // 3 is a big layer obscuring 2 with a dispatch-to-content region
+    LayerIntRegion layerVisibleRegions[] = {
+        LayerIntRect(0, 0, 100, 100),
+        LayerIntRect(0, 0, 0, 0),
+        LayerIntRect(0, 0, 10, 10),
+        LayerIntRect(0, 0, 100, 100),
+    };
+    Matrix4x4 layerTransforms[] = {
+        Matrix4x4(),
+        Matrix4x4::Translation(50, 0, 0),
+        Matrix4x4(),
+        Matrix4x4(),
+    };
+    CreateScrollData(treeShape, layerVisibleRegions, layerTransforms);
+
+    SetScrollableFrameMetrics(layers[2], ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 10, 10));
+    SetScrollableFrameMetrics(layers[3],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1,
+                              CSSRect(0, 0, 100, 100));
+    SetScrollHandoff(layers[3], layers[2]);
+
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+  }
+};
+
+class APZEventRegionsTesterMock : public APZEventRegionsTester {
+ public:
+  APZEventRegionsTesterMock() { CreateMockHitTester(); }
+};
+
+TEST_F(APZEventRegionsTesterMock, HitRegionImmediateResponse) {
+  CreateEventRegionsLayerTree1();
+
+  TestAsyncPanZoomController* root = ApzcOf(layers[0]);
+  TestAsyncPanZoomController* left = ApzcOf(layers[1]);
+  TestAsyncPanZoomController* bottom = ApzcOf(layers[2]);
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, _, _, left->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Tapped on left"));
+    EXPECT_CALL(*mcc,
+                HandleTap(TapType::eSingleTap, _, _, bottom->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Tapped on bottom"));
+    EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, _, _, root->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Tapped on root"));
+    EXPECT_CALL(check, Call("Tap pending on d-t-c region"));
+    EXPECT_CALL(*mcc,
+                HandleTap(TapType::eSingleTap, _, _, bottom->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Tapped on bottom again"));
+    EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, _, _, left->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Tapped on left this time"));
+  }
+
+  TimeDuration tapDuration = TimeDuration::FromMilliseconds(100);
+
+  // Tap in the exposed hit regions of each of the layers once and ensure
+  // the clicks are dispatched right away
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  Tap(manager, ScreenIntPoint(10, 10), tapDuration);
+  mcc->RunThroughDelayedTasks();  // this runs the tap event
+  check.Call("Tapped on left");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 2);
+  Tap(manager, ScreenIntPoint(110, 110), tapDuration);
+  mcc->RunThroughDelayedTasks();  // this runs the tap event
+  check.Call("Tapped on bottom");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  Tap(manager, ScreenIntPoint(110, 10), tapDuration);
+  mcc->RunThroughDelayedTasks();  // this runs the tap event
+  check.Call("Tapped on root");
+
+  // Now tap on the dispatch-to-content region where the layers overlap
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 2,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  Tap(manager, ScreenIntPoint(10, 110), tapDuration);
+  mcc->RunThroughDelayedTasks();  // this runs the main-thread timeout
+  check.Call("Tap pending on d-t-c region");
+  mcc->RunThroughDelayedTasks();  // this runs the tap event
+  check.Call("Tapped on bottom again");
+
+  // Now let's do that again, but simulate a main-thread response
+  uint64_t inputBlockId = 0;
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 2,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  Tap(manager, ScreenIntPoint(10, 110), tapDuration, nullptr, &inputBlockId);
+  nsTArray<ScrollableLayerGuid> targets;
+  targets.AppendElement(left->GetGuid());
+  manager->SetTargetAPZC(inputBlockId, targets);
+  while (mcc->RunThroughDelayedTasks())
+    ;  // this runs the tap event
+  check.Call("Tapped on left this time");
+}
+
+TEST_F(APZEventRegionsTesterMock, HitRegionAccumulatesChildren) {
+  CreateEventRegionsLayerTree2();
+
+  // Tap in the area of the child layer that's not directly included in the
+  // parent layer's hit region. Verify that it comes out of the APZC's
+  // content controller, which indicates the input events got routed correctly
+  // to the APZC.
+  EXPECT_CALL(*mcc,
+              HandleTap(TapType::eSingleTap, _, _, rootApzc->GetGuid(), _))
+      .Times(1);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  Tap(manager, ScreenIntPoint(10, 160), TimeDuration::FromMilliseconds(100));
+}
+
+TEST_F(APZEventRegionsTesterMock, Bug1117712) {
+  CreateBug1117712LayerTree();
+
+  TestAsyncPanZoomController* apzc2 = ApzcOf(layers[2]);
+
+  // These touch events should hit the dispatch-to-content region of layers[3]
+  // and so get queued with that APZC as the tentative target.
+  uint64_t inputBlockId = 0;
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  Tap(manager, ScreenIntPoint(55, 5), TimeDuration::FromMilliseconds(100),
+      nullptr, &inputBlockId);
+  // But now we tell the APZ that really it hit layers[2], and expect the tap
+  // to be delivered at the correct coordinates.
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(55, 5), 0,
+                              apzc2->GetGuid(), _))
+      .Times(1);
+
+  nsTArray<ScrollableLayerGuid> targets;
+  targets.AppendElement(apzc2->GetGuid());
+  manager->SetTargetAPZC(inputBlockId, targets);
+}
diff --git a/gfx/layers/apz/test/gtest/TestEventResult.cpp b/gfx/layers/apz/test/gtest/TestEventResult.cpp
new file mode 100644
index 0000000000..90d17ee511
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestEventResult.cpp
@@ -0,0 +1,476 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+#include "mozilla/EventForwards.h"
+#include "mozilla/layers/LayersTypes.h"
+#include <tuple>
+
+class APZEventResultTester : public APZCTreeManagerTester {
+ protected:
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+
+  void UpdateOverscrollBehavior(OverscrollBehavior aX, OverscrollBehavior aY) {
+    ModifyFrameMetrics(root, [aX, aY](ScrollMetadata& sm, FrameMetrics& _) {
+      OverscrollBehaviorInfo overscroll;
+      overscroll.mBehaviorX = aX;
+      overscroll.mBehaviorY = aY;
+      sm.SetOverscrollBehavior(overscroll);
+    });
+    UpdateHitTestingTree();
+  }
+
+  void SetScrollOffsetOnMainThread(const CSSPoint& aPoint) {
+    RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+
+    ScrollMetadata metadata = apzc->GetScrollMetadata();
+    metadata.GetMetrics().SetLayoutScrollOffset(aPoint);
+    nsTArray<ScrollPositionUpdate> scrollUpdates;
+    scrollUpdates.AppendElement(ScrollPositionUpdate::NewScroll(
+        ScrollOrigin::Other, CSSPoint::ToAppUnits(aPoint)));
+    metadata.SetScrollUpdates(scrollUpdates);
+    metadata.GetMetrics().SetScrollGeneration(
+        scrollUpdates.LastElement().GetGeneration());
+    apzc->NotifyLayersUpdated(metadata, /*aIsFirstPaint=*/false,
+                              /*aThisLayerTreeUpdated=*/true);
+  }
+
+  void CreateScrollableRootLayer() {
+    const char* treeShape = "x";
+    LayerIntRegion layerVisibleRegions[] = {
+        LayerIntRect(0, 0, 100, 100),
+    };
+    CreateScrollData(treeShape, layerVisibleRegions);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 200, 200));
+    ModifyFrameMetrics(root, [](ScrollMetadata& sm, FrameMetrics& metrics) {
+      metrics.SetIsRootContent(true);
+    });
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+  }
+
+  enum class PreventDefaultFlag { No, Yes };
+  std::tuple<APZEventResult, APZHandledResult> TapDispatchToContent(
+      const ScreenIntPoint& aPoint, PreventDefaultFlag aPreventDefaultFlag) {
+    APZEventResult result =
+        Tap(manager, aPoint, TimeDuration::FromMilliseconds(100));
+
+    APZHandledResult delayedAnswer{APZHandledPlace::Invalid, SideBits::eNone,
+                                   ScrollDirections()};
+    manager->AddInputBlockCallback(
+        result.mInputBlockId,
+        {result.GetStatus(), [&](uint64_t id, const APZHandledResult& answer) {
+           EXPECT_EQ(id, result.mInputBlockId);
+           delayedAnswer = answer;
+         }});
+    manager->SetAllowedTouchBehavior(result.mInputBlockId,
+                                     {AllowedTouchBehavior::VERTICAL_PAN});
+    manager->SetTargetAPZC(result.mInputBlockId, {result.mTargetGuid});
+    manager->ContentReceivedInputBlock(
+        result.mInputBlockId, aPreventDefaultFlag == PreventDefaultFlag::Yes);
+    return {result, delayedAnswer};
+  }
+
+  void OverscrollDirectionsWithEventHandlerTest(
+      PreventDefaultFlag aPreventDefaultFlag) {
+    UpdateHitTestingTree();
+
+    APZHandledPlace expectedPlace =
+        aPreventDefaultFlag == PreventDefaultFlag::No
+            ? APZHandledPlace::HandledByRoot
+            : APZHandledPlace::HandledByContent;
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eBottom | SideBits::eRight,
+                            EitherScrollDirection}));
+    }
+
+    // overscroll-behavior: contain, contain.
+    UpdateOverscrollBehavior(OverscrollBehavior::Contain,
+                             OverscrollBehavior::Contain);
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eBottom | SideBits::eRight,
+                            ScrollDirections()}));
+    }
+
+    // overscroll-behavior: none, none.
+    UpdateOverscrollBehavior(OverscrollBehavior::None,
+                             OverscrollBehavior::None);
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eBottom | SideBits::eRight,
+                            ScrollDirections()}));
+    }
+
+    // overscroll-behavior: auto, none.
+    UpdateOverscrollBehavior(OverscrollBehavior::Auto,
+                             OverscrollBehavior::None);
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eBottom | SideBits::eRight,
+                            HorizontalScrollDirection}));
+    }
+
+    // overscroll-behavior: none, auto.
+    UpdateOverscrollBehavior(OverscrollBehavior::None,
+                             OverscrollBehavior::Auto);
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eBottom | SideBits::eRight,
+                            VerticalScrollDirection}));
+    }
+  }
+
+  void ScrollableDirectionsWithEventHandlerTest(
+      PreventDefaultFlag aPreventDefaultFlag) {
+    UpdateHitTestingTree();
+
+    APZHandledPlace expectedPlace =
+        aPreventDefaultFlag == PreventDefaultFlag::No
+            ? APZHandledPlace::HandledByRoot
+            : APZHandledPlace::HandledByContent;
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eBottom | SideBits::eRight,
+                            EitherScrollDirection}));
+    }
+
+    // scroll down a bit.
+    SetScrollOffsetOnMainThread(CSSPoint(0, 10));
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(delayedHandledResult,
+                (APZHandledResult{
+                    expectedPlace,
+                    SideBits::eTop | SideBits::eBottom | SideBits::eRight,
+                    EitherScrollDirection}));
+    }
+
+    // scroll to the bottom edge
+    SetScrollOffsetOnMainThread(CSSPoint(0, 100));
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eRight | SideBits::eTop,
+                            EitherScrollDirection}));
+    }
+
+    // scroll to right a bit.
+    SetScrollOffsetOnMainThread(CSSPoint(10, 100));
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace,
+                            SideBits::eLeft | SideBits::eRight | SideBits::eTop,
+                            EitherScrollDirection}));
+    }
+
+    // scroll to the right edge.
+    SetScrollOffsetOnMainThread(CSSPoint(100, 100));
+    {
+      QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                         {CompositorHitTestFlags::eVisibleToHitTest,
+                          CompositorHitTestFlags::eIrregularArea});
+      auto [result, delayedHandledResult] =
+          TapDispatchToContent(ScreenIntPoint(50, 50), aPreventDefaultFlag);
+      EXPECT_EQ(result.GetHandledResult(), Nothing());
+      EXPECT_EQ(
+          delayedHandledResult,
+          (APZHandledResult{expectedPlace, SideBits::eTop | SideBits::eLeft,
+                            EitherScrollDirection}));
+    }
+  }
+};
+
+TEST_F(APZEventResultTester, OverscrollDirections) {
+  CreateScrollableRootLayer();
+
+  TimeDuration tapDuration = TimeDuration::FromMilliseconds(100);
+
+  // The default value of overscroll-behavior is auto.
+  APZEventResult result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mOverscrollDirections,
+            EitherScrollDirection);
+
+  // overscroll-behavior: contain, contain.
+  UpdateOverscrollBehavior(OverscrollBehavior::Contain,
+                           OverscrollBehavior::Contain);
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mOverscrollDirections,
+            ScrollDirections());
+
+  // overscroll-behavior: none, none.
+  UpdateOverscrollBehavior(OverscrollBehavior::None, OverscrollBehavior::None);
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mOverscrollDirections,
+            ScrollDirections());
+
+  // overscroll-behavior: auto, none.
+  UpdateOverscrollBehavior(OverscrollBehavior::Auto, OverscrollBehavior::None);
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mOverscrollDirections,
+            HorizontalScrollDirection);
+
+  // overscroll-behavior: none, auto.
+  UpdateOverscrollBehavior(OverscrollBehavior::None, OverscrollBehavior::Auto);
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mOverscrollDirections,
+            VerticalScrollDirection);
+}
+
+TEST_F(APZEventResultTester, ScrollableDirections) {
+  CreateScrollableRootLayer();
+
+  TimeDuration tapDuration = TimeDuration::FromMilliseconds(100);
+
+  APZEventResult result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  // scrollable to down/right.
+  EXPECT_EQ(result.GetHandledResult()->mScrollableDirections,
+            SideBits::eBottom | SideBits::eRight);
+
+  // scroll down a bit.
+  SetScrollOffsetOnMainThread(CSSPoint(0, 10));
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  // also scrollable toward top.
+  EXPECT_EQ(result.GetHandledResult()->mScrollableDirections,
+            SideBits::eTop | SideBits::eBottom | SideBits::eRight);
+
+  // scroll to the bottom edge
+  SetScrollOffsetOnMainThread(CSSPoint(0, 100));
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mScrollableDirections,
+            SideBits::eRight | SideBits::eTop);
+
+  // scroll to right a bit.
+  SetScrollOffsetOnMainThread(CSSPoint(10, 100));
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mScrollableDirections,
+            SideBits::eLeft | SideBits::eRight | SideBits::eTop);
+
+  // scroll to the right edge.
+  SetScrollOffsetOnMainThread(CSSPoint(100, 100));
+  result = Tap(manager, ScreenIntPoint(50, 50), tapDuration);
+  EXPECT_EQ(result.GetHandledResult()->mScrollableDirections,
+            SideBits::eLeft | SideBits::eTop);
+}
+
+class APZEventResultTesterMock : public APZEventResultTester {
+ public:
+  APZEventResultTesterMock() { CreateMockHitTester(); }
+};
+
+TEST_F(APZEventResultTesterMock, OverscrollDirectionsWithEventHandler) {
+  CreateScrollableRootLayer();
+
+  OverscrollDirectionsWithEventHandlerTest(PreventDefaultFlag::No);
+}
+
+TEST_F(APZEventResultTesterMock,
+       OverscrollDirectionsWithPreventDefaultEventHandler) {
+  CreateScrollableRootLayer();
+
+  OverscrollDirectionsWithEventHandlerTest(PreventDefaultFlag::Yes);
+}
+
+TEST_F(APZEventResultTesterMock, ScrollableDirectionsWithEventHandler) {
+  CreateScrollableRootLayer();
+
+  ScrollableDirectionsWithEventHandlerTest(PreventDefaultFlag::No);
+}
+
+TEST_F(APZEventResultTesterMock,
+       ScrollableDirectionsWithPreventDefaultEventHandler) {
+  CreateScrollableRootLayer();
+
+  ScrollableDirectionsWithEventHandlerTest(PreventDefaultFlag::Yes);
+}
+
+// Test that APZEventResult::GetHandledResult() is correctly
+// populated.
+TEST_F(APZEventResultTesterMock, HandledByRootApzcFlag) {
+  // Create simple layer tree containing a dispatch-to-content region
+  // that covers part but not all of its area.
+  const char* treeShape = "x";
+  LayerIntRegion layerVisibleRegions[] = {
+      LayerIntRect(0, 0, 100, 100),
+  };
+  CreateScrollData(treeShape, layerVisibleRegions);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 200));
+  ModifyFrameMetrics(root, [](ScrollMetadata& sm, FrameMetrics& metrics) {
+    metrics.SetIsRootContent(true);
+  });
+  // away from the scrolling container layer.
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  // Tap the top half and check that we report that the event was
+  // handled by the root APZC.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  APZEventResult result =
+      TouchDown(manager, ScreenIntPoint(50, 25), mcc->Time());
+  TouchUp(manager, ScreenIntPoint(50, 25), mcc->Time());
+  EXPECT_EQ(result.GetHandledResult(),
+            Some(APZHandledResult{APZHandledPlace::HandledByRoot,
+                                  SideBits::eBottom, EitherScrollDirection}));
+
+  // Tap the bottom half and check that we report that we're not
+  // sure whether the event was handled by the root APZC.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  result = TouchDown(manager, ScreenIntPoint(50, 75), mcc->Time());
+  TouchUp(manager, ScreenIntPoint(50, 75), mcc->Time());
+  EXPECT_EQ(result.GetHandledResult(), Nothing());
+
+  // Register an input block callback that will tell us the
+  // delayed answer.
+  APZHandledResult delayedAnswer{APZHandledPlace::Invalid, SideBits::eNone,
+                                 ScrollDirections()};
+  manager->AddInputBlockCallback(
+      result.mInputBlockId,
+      {result.GetStatus(), [&](uint64_t id, const APZHandledResult& answer) {
+         EXPECT_EQ(id, result.mInputBlockId);
+         delayedAnswer = answer;
+       }});
+
+  // Send APZ the relevant notifications to allow it to process the
+  // input block.
+  manager->SetAllowedTouchBehavior(result.mInputBlockId,
+                                   {AllowedTouchBehavior::VERTICAL_PAN});
+  manager->SetTargetAPZC(result.mInputBlockId, {result.mTargetGuid});
+  manager->ContentReceivedInputBlock(result.mInputBlockId,
+                                     /*aPreventDefault=*/false);
+
+  // Check that we received the delayed answer and it is what we expect.
+  EXPECT_EQ(delayedAnswer,
+            (APZHandledResult{APZHandledPlace::HandledByRoot, SideBits::eBottom,
+                              EitherScrollDirection}));
+
+  // Now repeat the tap on the bottom half, but simulate a prevent-default.
+  // This time, we expect a delayed answer of `HandledByContent`.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  result = TouchDown(manager, ScreenIntPoint(50, 75), mcc->Time());
+  TouchUp(manager, ScreenIntPoint(50, 75), mcc->Time());
+  EXPECT_EQ(result.GetHandledResult(), Nothing());
+  manager->AddInputBlockCallback(
+      result.mInputBlockId,
+      {result.GetStatus(), [&](uint64_t id, const APZHandledResult& answer) {
+         EXPECT_EQ(id, result.mInputBlockId);
+         delayedAnswer = answer;
+       }});
+  manager->SetAllowedTouchBehavior(result.mInputBlockId,
+                                   {AllowedTouchBehavior::VERTICAL_PAN});
+  manager->SetTargetAPZC(result.mInputBlockId, {result.mTargetGuid});
+  manager->ContentReceivedInputBlock(result.mInputBlockId,
+                                     /*aPreventDefault=*/true);
+  EXPECT_EQ(delayedAnswer,
+            (APZHandledResult{APZHandledPlace::HandledByContent,
+                              SideBits::eBottom, EitherScrollDirection}));
+
+  // Shrink the scrollable area, now it's no longer scrollable.
+  ModifyFrameMetrics(root, [](ScrollMetadata& sm, FrameMetrics& metrics) {
+    metrics.SetScrollableRect(CSSRect(0, 0, 100, 100));
+  });
+  UpdateHitTestingTree();
+  // Now repeat the tap on the bottom half with an event handler.
+  // This time, we expect a delayed answer of `Unhandled`.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  result = TouchDown(manager, ScreenIntPoint(50, 75), mcc->Time());
+  TouchUp(manager, ScreenIntPoint(50, 75), mcc->Time());
+  EXPECT_EQ(result.GetHandledResult(), Nothing());
+  manager->AddInputBlockCallback(
+      result.mInputBlockId,
+      {result.GetStatus(), [&](uint64_t id, const APZHandledResult& answer) {
+         EXPECT_EQ(id, result.mInputBlockId);
+         delayedAnswer = answer;
+       }});
+  manager->SetAllowedTouchBehavior(result.mInputBlockId,
+                                   {AllowedTouchBehavior::VERTICAL_PAN});
+  manager->SetTargetAPZC(result.mInputBlockId, {result.mTargetGuid});
+  manager->ContentReceivedInputBlock(result.mInputBlockId,
+                                     /*aPreventDefault=*/false);
+  EXPECT_EQ(delayedAnswer,
+            (APZHandledResult{APZHandledPlace::Unhandled, SideBits::eNone,
+                              ScrollDirections()}));
+
+  // Repeat the tap on the bottom half, with no event handler.
+  // Make sure we get an eager answer of `Unhandled`.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  result = TouchDown(manager, ScreenIntPoint(50, 75), mcc->Time());
+  TouchUp(manager, ScreenIntPoint(50, 75), mcc->Time());
+  EXPECT_EQ(result.GetStatus(), nsEventStatus_eIgnore);
+  EXPECT_EQ(result.GetHandledResult(),
+            Some(APZHandledResult{APZHandledPlace::Unhandled, SideBits::eNone,
+                                  EitherScrollDirection}));
+}
diff --git a/gfx/layers/apz/test/gtest/TestFlingAcceleration.cpp b/gfx/layers/apz/test/gtest/TestFlingAcceleration.cpp
new file mode 100644
index 0000000000..986025bddc
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestFlingAcceleration.cpp
@@ -0,0 +1,252 @@
+/* -*- 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 <initializer_list>
+#include "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+
+class APZCFlingAccelerationTester : public APZCTreeManagerTester {
+ protected:
+  void SetUp() {
+    APZCTreeManagerTester::SetUp();
+    const char* treeShape = "x";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 800, 1000),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 800, 50000));
+    // Scroll somewhere into the middle of the scroll range, so that we have
+    // lots of space to scroll in both directions.
+    ModifyFrameMetrics(root, [](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+      aMetrics.SetVisualScrollUpdateType(
+          FrameMetrics::ScrollOffsetUpdateType::eMainThread);
+      aMetrics.SetVisualDestination(CSSPoint(0, 25000));
+    });
+
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+
+    apzc = ApzcOf(root);
+  }
+
+  void ExecutePanGesture100Hz(const ScreenIntPoint& aStartPoint,
+                              std::initializer_list<int32_t> aYDeltas) {
+    APZEventResult result = TouchDown(apzc, aStartPoint, mcc->Time());
+
+    // Allowed touch behaviours must be set after sending touch-start.
+    if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+      SetDefaultAllowedTouchBehavior(apzc, result.mInputBlockId);
+    }
+
+    const TimeDuration kTouchTimeDelta100Hz =
+        TimeDuration::FromMilliseconds(10);
+
+    ScreenIntPoint currentLocation = aStartPoint;
+    for (int32_t delta : aYDeltas) {
+      mcc->AdvanceBy(kTouchTimeDelta100Hz);
+      if (delta != 0) {
+        currentLocation.y += delta;
+        Unused << TouchMove(apzc, currentLocation, mcc->Time());
+      }
+    }
+
+    Unused << TouchUp(apzc, currentLocation, mcc->Time());
+  }
+
+  void ExecuteWait(const TimeDuration& aDuration) {
+    TimeDuration remaining = aDuration;
+    const TimeDuration TIME_BETWEEN_FRAMES =
+        TimeDuration::FromSeconds(1) / int64_t(60);
+    while (remaining.ToMilliseconds() > 0) {
+      mcc->AdvanceBy(TIME_BETWEEN_FRAMES);
+      apzc->AdvanceAnimations(mcc->GetSampleTime());
+      remaining -= TIME_BETWEEN_FRAMES;
+    }
+  }
+
+  RefPtr<TestAsyncPanZoomController> apzc;
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+};
+
+enum class UpOrDown : uint8_t { Up, Down };
+
+// This is a macro so that the assertions print useful line numbers.
+#define CHECK_VELOCITY(aUpOrDown, aLowerBound, aUpperBound) \
+  do {                                                      \
+    auto vel = apzc->GetVelocityVector();                   \
+    if (UpOrDown::aUpOrDown == UpOrDown::Up) {              \
+      EXPECT_LT(vel.y, 0.0);                                \
+    } else {                                                \
+      EXPECT_GT(vel.y, 0.0);                                \
+    }                                                       \
+    EXPECT_GE(vel.Length(), aLowerBound);                   \
+    EXPECT_LE(vel.Length(), aUpperBound);                   \
+  } while (0)
+
+// These tests have the following pattern: Two flings are executed, with a bit
+// of wait time in between. The deltas in each pan gesture have been captured
+// from a real phone, from touch events triggered by real fingers.
+// We check the velocity at the end to detect whether the fling was accelerated
+// or not. As an additional safety precaution, we also check the velocities for
+// the first fling, so that changes in behavior are easier to analyze.
+// One added challenge of this test is the fact that it has to work with on
+// multiple platforms, and we use different velocity estimation strategies and
+// different fling physics depending on the platform.
+// The upper and lower bounds for the velocities were chosen in such a way that
+// the test passes on all platforms. At the time of writing, we usually end up
+// with higher velocities on Android than on Desktop, so the observed velocities
+// on Android became the upper bounds and the observed velocities on Desktop
+// becaume the lower bounds, each rounded out to a multiple of 0.1.
+
+TEST_F(APZCFlingAccelerationTester, TwoNormalFlingsShouldAccelerate) {
+  ExecutePanGesture100Hz(ScreenIntPoint{665, 1244},
+                         {0, 0, -21, -44, -52, -55, -53, -49, -46, -47});
+  CHECK_VELOCITY(Down, 4.5, 6.8);
+
+  ExecuteWait(TimeDuration::FromMilliseconds(375));
+  CHECK_VELOCITY(Down, 2.2, 5.1);
+
+  ExecutePanGesture100Hz(ScreenIntPoint{623, 1211},
+                         {-6, -51, -55, 0, -53, -57, -60, -60, -56});
+  CHECK_VELOCITY(Down, 9.0, 14.0);
+}
+
+TEST_F(APZCFlingAccelerationTester, TwoFastFlingsShouldAccelerate) {
+  ExecutePanGesture100Hz(ScreenIntPoint{764, 714},
+                         {9, 30, 49, 60, 64, 64, 62, 59, 51});
+  CHECK_VELOCITY(Up, 5.0, 7.5);
+
+  ExecuteWait(TimeDuration::FromMilliseconds(447));
+  CHECK_VELOCITY(Up, 2.3, 5.2);
+
+  ExecutePanGesture100Hz(ScreenIntPoint{743, 739},
+                         {7, 0, 38, 66, 75, 146, 0, 119});
+  CHECK_VELOCITY(Up, 13.0, 20.0);
+}
+
+TEST_F(APZCFlingAccelerationTester,
+       FlingsInOppositeDirectionShouldNotAccelerate) {
+  ExecutePanGesture100Hz(ScreenIntPoint{728, 1381},
+                         {0, 0, 0, -12, -24, -32, -43, -46, 0});
+  CHECK_VELOCITY(Down, 2.9, 5.3);
+
+  ExecuteWait(TimeDuration::FromMilliseconds(153));
+  CHECK_VELOCITY(Down, 2.1, 4.8);
+
+  ExecutePanGesture100Hz(ScreenIntPoint{698, 1059},
+                         {0, 0, 14, 61, 41, 0, 45, 35});
+  CHECK_VELOCITY(Up, 3.2, 4.3);
+}
+
+TEST_F(APZCFlingAccelerationTester,
+       ShouldNotAccelerateWhenPreviousFlingHasSlowedDown) {
+  ExecutePanGesture100Hz(ScreenIntPoint{748, 1046},
+                         {0, 9, 15, 23, 31, 30, 0, 34, 31, 29, 28, 24, 24, 11});
+  CHECK_VELOCITY(Up, 2.2, 3.0);
+  ExecuteWait(TimeDuration::FromMilliseconds(498));
+  CHECK_VELOCITY(Up, 0.5, 1.0);
+  ExecutePanGesture100Hz(ScreenIntPoint{745, 1056},
+                         {0, 10, 17, 29, 29, 33, 33, 0, 31, 27, 13});
+  CHECK_VELOCITY(Up, 1.8, 2.7);
+}
+
+TEST_F(APZCFlingAccelerationTester, ShouldNotAccelerateWhenPausedAtStartOfPan) {
+  ExecutePanGesture100Hz(
+      ScreenIntPoint{711, 1468},
+      {0, 0, 0, 0, -8, 0, -18, -32, -50, -57, -66, -68, -63, -60});
+  CHECK_VELOCITY(Down, 6.2, 8.6);
+
+  ExecuteWait(TimeDuration::FromMilliseconds(285));
+  CHECK_VELOCITY(Down, 3.4, 7.4);
+
+  ExecutePanGesture100Hz(
+      ScreenIntPoint{658, 1352},
+      {0, 0, 0, 0, 0, 0,  0,   0,   0,   0,   0,   0,   0,
+       0, 0, 0, 0, 0, -8, -18, -34, -53, -70, -75, -75, -64});
+  CHECK_VELOCITY(Down, 6.7, 9.1);
+}
+
+TEST_F(APZCFlingAccelerationTester, ShouldNotAccelerateWhenPausedDuringPan) {
+  ExecutePanGesture100Hz(
+      ScreenIntPoint{732, 1423},
+      {0, 0, 0, -5, 0, -15, -41, -71, -90, -93, -85, -64, -44});
+  CHECK_VELOCITY(Down, 7.5, 10.1);
+
+  ExecuteWait(TimeDuration::FromMilliseconds(204));
+  CHECK_VELOCITY(Down, 4.8, 9.4);
+
+  ExecutePanGesture100Hz(
+      ScreenIntPoint{651, 1372},
+      {0,   0,   0,  -6, 0,  -16, -26, -41, -49, -65, -66, -61, -50, -35, -24,
+       -17, -11, -8, -6, -5, -4,  -3,  -2,  -2,  -2,  -2,  -2,  -2,  -2,  -2,
+       -3,  -4,  -5, -7, -9, -10, -10, -12, -18, -25, -23, -28, -30, -24});
+  CHECK_VELOCITY(Down, 2.5, 3.4);
+}
+
+TEST_F(APZCFlingAccelerationTester,
+       ShouldNotAccelerateWhenOppositeDirectionDuringPan) {
+  ExecutePanGesture100Hz(ScreenIntPoint{663, 1371},
+                         {0, 0, 0, -5, -18, -31, -49, -56, -61, -54, -55});
+  CHECK_VELOCITY(Down, 5.4, 7.1);
+
+  ExecuteWait(TimeDuration::FromMilliseconds(255));
+  CHECK_VELOCITY(Down, 3.1, 6.0);
+
+  ExecutePanGesture100Hz(
+      ScreenIntPoint{726, 930},
+      {0,  0,   0,   0,   30,  0,   19,  24,  32,  30, 37, 33,
+       33, 32,  25,  23,  23,  18,  13,  9,   5,   3,  1,  0,
+       -7, -19, -38, -53, -68, -79, -85, -73, -64, -54});
+  CHECK_VELOCITY(Down, 7.0, 10.0);
+}
+
+TEST_F(APZCFlingAccelerationTester,
+       ShouldAccelerateAfterLongWaitIfVelocityStillHigh) {
+  // Reduce friction with the "Desktop" fling physics a little, so that it
+  // behaves more similarly to the Android fling physics, and has enough
+  // velocity after the wait time to allow for acceleration.
+  SCOPED_GFX_PREF_FLOAT("apz.fling_friction", 0.0012);
+
+  ExecutePanGesture100Hz(ScreenIntPoint{739, 1424},
+                         {0, 0, -5, -10, -20, 0, -110, -86, 0, -102, -105});
+  CHECK_VELOCITY(Down, 6.3, 9.4);
+
+  ExecuteWait(TimeDuration::FromMilliseconds(1117));
+  CHECK_VELOCITY(Down, 1.6, 3.3);
+
+  ExecutePanGesture100Hz(ScreenIntPoint{726, 1380},
+                         {0, -8, 0, -30, -60, -87, -104, -111});
+  CHECK_VELOCITY(Down, 13.0, 23.0);
+}
+
+TEST_F(APZCFlingAccelerationTester, ShouldNotAccelerateAfterCanceledWithTap) {
+  // First, build up a lot of speed.
+  ExecutePanGesture100Hz(ScreenIntPoint{569, 710},
+                         {11, 2, 107, 18, 148, 57, 133, 159, 21});
+  ExecuteWait(TimeDuration::FromMilliseconds(154));
+  ExecutePanGesture100Hz(ScreenIntPoint{581, 650},
+                         {12, 68, 0, 162, 78, 140, 167});
+  ExecuteWait(TimeDuration::FromMilliseconds(123));
+  ExecutePanGesture100Hz(ScreenIntPoint{568, 723}, {11, 0, 79, 91, 131, 171});
+  ExecuteWait(TimeDuration::FromMilliseconds(123));
+  ExecutePanGesture100Hz(ScreenIntPoint{598, 678},
+                         {8, 55, 22, 87, 117, 220, 54});
+  ExecuteWait(TimeDuration::FromMilliseconds(134));
+  ExecutePanGesture100Hz(ScreenIntPoint{585, 854}, {45, 137, 107, 102, 79});
+  ExecuteWait(TimeDuration::FromMilliseconds(246));
+
+  // Then, interrupt with a tap.
+  ExecutePanGesture100Hz(ScreenIntPoint{566, 812}, {0, 0, 0, 0});
+  ExecuteWait(TimeDuration::FromMilliseconds(869));
+
+  // Then do a regular fling.
+  ExecutePanGesture100Hz(ScreenIntPoint{599, 819},
+                         {0, 0, 8, 35, 8, 38, 29, 37});
+
+  CHECK_VELOCITY(Up, 2.8, 4.2);
+}
diff --git a/gfx/layers/apz/test/gtest/TestGestureDetector.cpp b/gfx/layers/apz/test/gtest/TestGestureDetector.cpp
new file mode 100644
index 0000000000..ad5f379ba8
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestGestureDetector.cpp
@@ -0,0 +1,849 @@
+/* -*- 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 "APZCBasicTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+#include "mozilla/StaticPrefs_apz.h"
+
+// Note: There are additional tests that test gesture detection behaviour
+//       with multiple APZCs in TestTreeManager.cpp.
+
+class APZCGestureDetectorTester : public APZCBasicTester {
+ public:
+  APZCGestureDetectorTester()
+      : APZCBasicTester(AsyncPanZoomController::USE_GESTURE_DETECTOR) {}
+
+ protected:
+  FrameMetrics GetPinchableFrameMetrics() {
+    FrameMetrics fm;
+    fm.SetCompositionBounds(ParentLayerRect(200, 200, 100, 200));
+    fm.SetScrollableRect(CSSRect(0, 0, 980, 1000));
+    fm.SetVisualScrollOffset(CSSPoint(300, 300));
+    fm.SetZoom(CSSToParentLayerScale(2.0));
+    // APZC only allows zooming on the root scrollable frame.
+    fm.SetIsRootContent(true);
+    // the visible area of the document in CSS pixels is x=300 y=300 w=50 h=100
+    return fm;
+  }
+};
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCGestureDetectorTester, Pan_After_Pinch) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 2);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.lock_angle", M_PI / 6.0f);
+  SCOPED_GFX_PREF_FLOAT("apz.axis_lock.breakout_angle", M_PI / 8.0f);
+
+  FrameMetrics originalMetrics = GetPinchableFrameMetrics();
+  apzc->SetFrameMetrics(originalMetrics);
+
+  MakeApzcZoomable();
+
+  // Test parameters
+  float zoomAmount = 1.25;
+  float pinchLength = 100.0;
+  float pinchLengthScaled = pinchLength * zoomAmount;
+  int focusX = 250;
+  int focusY = 300;
+  int panDistance = 20;
+  const TimeDuration TIME_BETWEEN_TOUCH_EVENT =
+      TimeDuration::FromMilliseconds(50);
+
+  int firstFingerId = 0;
+  int secondFingerId = firstFingerId + 1;
+
+  // Put fingers down
+  MultiTouchInput mti =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_START, 0, mcc->Time(), 0);
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, focusX, focusY));
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(secondFingerId, focusX, focusY));
+  apzc->ReceiveInputEvent(mti, Some(nsTArray<uint32_t>{kDefaultTouchBehavior}));
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // Spread fingers out to enter the pinch state
+  mti = MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, focusX - pinchLength, focusY));
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(secondFingerId, focusX + pinchLength, focusY));
+  apzc->ReceiveInputEvent(mti);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // Do the actual pinch of 1.25x
+  mti = MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, focusX - pinchLengthScaled, focusY));
+  mti.mTouches.AppendElement(CreateSingleTouchData(
+      secondFingerId, focusX + pinchLengthScaled, focusY));
+  apzc->ReceiveInputEvent(mti);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // Verify that the zoom changed, just to make sure our code above did what it
+  // was supposed to.
+  FrameMetrics zoomedMetrics = apzc->GetFrameMetrics();
+  float newZoom = zoomedMetrics.GetZoom().scale;
+  EXPECT_EQ(originalMetrics.GetZoom().scale * zoomAmount, newZoom);
+
+  // Now we lift one finger...
+  mti = MultiTouchInput(MultiTouchInput::MULTITOUCH_END, 0, mcc->Time(), 0);
+  mti.mTouches.AppendElement(CreateSingleTouchData(
+      secondFingerId, focusX + pinchLengthScaled, focusY));
+  apzc->ReceiveInputEvent(mti);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // ... and pan with the remaining finger. This pan just breaks through the
+  // distance threshold.
+  focusY += StaticPrefs::apz_touch_start_tolerance() * tm->GetDPI();
+  mti = MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, focusX - pinchLengthScaled, focusY));
+  apzc->ReceiveInputEvent(mti);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // This one does an actual pan of 20 pixels
+  focusY += panDistance;
+  mti = MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, focusX - pinchLengthScaled, focusY));
+  apzc->ReceiveInputEvent(mti);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // Lift the remaining finger
+  mti = MultiTouchInput(MultiTouchInput::MULTITOUCH_END, 0, mcc->Time(), 0);
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, focusX - pinchLengthScaled, focusY));
+  apzc->ReceiveInputEvent(mti);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  // Verify that we scrolled
+  FrameMetrics finalMetrics = apzc->GetFrameMetrics();
+  EXPECT_EQ(zoomedMetrics.GetVisualScrollOffset().y - (panDistance / newZoom),
+            finalMetrics.GetVisualScrollOffset().y);
+
+  // Clear out any remaining fling animation and pending tasks
+  apzc->AdvanceAnimationsUntilEnd();
+  while (mcc->RunThroughDelayedTasks())
+    ;
+  apzc->AssertStateIsReset();
+}
+#endif
+
+TEST_F(APZCGestureDetectorTester, Pan_With_Tap) {
+  SCOPED_GFX_PREF_FLOAT("apz.touch_start_tolerance", 0.1);
+
+  FrameMetrics originalMetrics = GetPinchableFrameMetrics();
+  apzc->SetFrameMetrics(originalMetrics);
+
+  // Making the APZC zoomable isn't really needed for the correct operation of
+  // this test, but it could help catch regressions where we accidentally enter
+  // a pinch state.
+  MakeApzcZoomable();
+
+  // Test parameters
+  int touchX = 250;
+  int touchY = 300;
+  int panDistance = 20;
+
+  int firstFingerId = 0;
+  int secondFingerId = firstFingerId + 1;
+
+  const float panThreshold =
+      StaticPrefs::apz_touch_start_tolerance() * tm->GetDPI();
+
+  // Put finger down
+  MultiTouchInput mti =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, touchX, touchY));
+  apzc->ReceiveInputEvent(mti, Some(nsTArray<uint32_t>{kDefaultTouchBehavior}));
+
+  // Start a pan, break through the threshold
+  touchY += panThreshold;
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, touchX, touchY));
+  apzc->ReceiveInputEvent(mti);
+
+  // Do an actual pan for a bit
+  touchY += panDistance;
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, touchX, touchY));
+  apzc->ReceiveInputEvent(mti);
+
+  // Put a second finger down
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, touchX, touchY));
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(secondFingerId, touchX + 10, touchY));
+  apzc->ReceiveInputEvent(mti, Some(nsTArray<uint32_t>{kDefaultTouchBehavior}));
+
+  // Lift the second finger
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_END, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(secondFingerId, touchX + 10, touchY));
+  apzc->ReceiveInputEvent(mti);
+
+  // Bust through the threshold again
+  touchY += panThreshold;
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, touchX, touchY));
+  apzc->ReceiveInputEvent(mti);
+
+  // Do some more actual panning
+  touchY += panDistance;
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, touchX, touchY));
+  apzc->ReceiveInputEvent(mti);
+
+  // Lift the first finger
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_END, mcc->Time());
+  mti.mTouches.AppendElement(
+      CreateSingleTouchData(firstFingerId, touchX, touchY));
+  apzc->ReceiveInputEvent(mti);
+
+  // Verify that we scrolled
+  FrameMetrics finalMetrics = apzc->GetFrameMetrics();
+  float zoom = finalMetrics.GetZoom().scale;
+  EXPECT_EQ(
+      originalMetrics.GetVisualScrollOffset().y - (panDistance * 2 / zoom),
+      finalMetrics.GetVisualScrollOffset().y);
+
+  // Clear out any remaining fling animation and pending tasks
+  apzc->AdvanceAnimationsUntilEnd();
+  while (mcc->RunThroughDelayedTasks())
+    ;
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCGestureDetectorTester, SecondTapIsFar_Bug1586496) {
+  // Test that we receive two single-tap events when two tap gestures are
+  // close in time but far in distance.
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, _, 0, apzc->GetGuid(), _))
+      .Times(2);
+
+  TimeDuration brief =
+      TimeDuration::FromMilliseconds(StaticPrefs::apz_max_tap_time() / 10.0);
+
+  ScreenIntPoint point(10, 10);
+  Tap(apzc, point, brief);
+
+  mcc->AdvanceBy(brief);
+
+  point.x += apzc->GetSecondTapTolerance() * 2;
+  point.y += apzc->GetSecondTapTolerance() * 2;
+
+  Tap(apzc, point, brief);
+}
+
+class APZCFlingStopTester : public APZCGestureDetectorTester {
+ protected:
+  // Start a fling, and then tap while the fling is ongoing. When
+  // aSlow is false, the tap will happen while the fling is at a
+  // high velocity, and we check that the tap doesn't trigger sending a tap
+  // to content. If aSlow is true, the tap will happen while the fling
+  // is at a slow velocity, and we check that the tap does trigger sending
+  // a tap to content. See bug 1022956.
+  void DoFlingStopTest(bool aSlow) {
+    int touchStart = 50;
+    int touchEnd = 10;
+
+    // Start the fling down.
+    Pan(apzc, touchStart, touchEnd);
+    // The touchstart from the pan will leave some cancelled tasks in the queue,
+    // clear them out
+
+    // If we want to tap while the fling is fast, let the fling advance for 10ms
+    // only. If we want the fling to slow down more, advance to 2000ms. These
+    // numbers may need adjusting if our friction and threshold values change,
+    // but they should be deterministic at least.
+    int timeDelta = aSlow ? 2000 : 10;
+    int tapCallsExpected = aSlow ? 2 : 1;
+
+    // Advance the fling animation by timeDelta milliseconds.
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+    apzc->SampleContentTransformForFrame(
+        &viewTransformOut, pointOut, TimeDuration::FromMilliseconds(timeDelta));
+
+    // Deliver a tap to abort the fling. Ensure that we get a SingleTap
+    // call out of it if and only if the fling is slow.
+    EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, _, 0, apzc->GetGuid(), _))
+        .Times(tapCallsExpected);
+    Tap(apzc, ScreenIntPoint(10, 10), 0);
+    while (mcc->RunThroughDelayedTasks())
+      ;
+
+    // Deliver another tap, to make sure that taps are flowing properly once
+    // the fling is aborted.
+    Tap(apzc, ScreenIntPoint(100, 100), 0);
+    while (mcc->RunThroughDelayedTasks())
+      ;
+
+    // Verify that we didn't advance any further after the fling was aborted, in
+    // either case.
+    ParentLayerPoint finalPointOut;
+    apzc->SampleContentTransformForFrame(&viewTransformOut, finalPointOut);
+    EXPECT_EQ(pointOut.x, finalPointOut.x);
+    EXPECT_EQ(pointOut.y, finalPointOut.y);
+
+    apzc->AssertStateIsReset();
+  }
+
+  void DoFlingStopWithSlowListener(bool aPreventDefault) {
+    MakeApzcWaitForMainThread();
+
+    int touchStart = 50;
+    int touchEnd = 10;
+    uint64_t blockId = 0;
+
+    // Start the fling down.
+    Pan(apzc, touchStart, touchEnd, PanOptions::None, nullptr, nullptr,
+        &blockId);
+    apzc->ConfirmTarget(blockId);
+    apzc->ContentReceivedInputBlock(blockId, false);
+
+    // Sample the fling a couple of times to ensure it's going.
+    ParentLayerPoint point, finalPoint;
+    AsyncTransform viewTransform;
+    apzc->SampleContentTransformForFrame(&viewTransform, point,
+                                         TimeDuration::FromMilliseconds(10));
+    apzc->SampleContentTransformForFrame(&viewTransform, finalPoint,
+                                         TimeDuration::FromMilliseconds(10));
+    EXPECT_GT(finalPoint.y, point.y);
+
+    // Now we put our finger down to stop the fling
+    blockId =
+        TouchDown(apzc, ScreenIntPoint(10, 10), mcc->Time()).mInputBlockId;
+
+    // Re-sample to make sure it hasn't moved
+    apzc->SampleContentTransformForFrame(&viewTransform, point,
+                                         TimeDuration::FromMilliseconds(10));
+    EXPECT_EQ(finalPoint.x, point.x);
+    EXPECT_EQ(finalPoint.y, point.y);
+
+    // respond to the touchdown that stopped the fling.
+    // even if we do a prevent-default on it, the animation should remain
+    // stopped.
+    apzc->ContentReceivedInputBlock(blockId, aPreventDefault);
+
+    // Verify the page hasn't moved
+    apzc->SampleContentTransformForFrame(&viewTransform, point,
+                                         TimeDuration::FromMilliseconds(70));
+    EXPECT_EQ(finalPoint.x, point.x);
+    EXPECT_EQ(finalPoint.y, point.y);
+
+    // clean up
+    TouchUp(apzc, ScreenIntPoint(10, 10), mcc->Time());
+
+    apzc->AssertStateIsReset();
+  }
+};
+
+TEST_F(APZCFlingStopTester, FlingStop) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+  DoFlingStopTest(false);
+}
+
+TEST_F(APZCFlingStopTester, FlingStopTap) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+  DoFlingStopTest(true);
+}
+
+TEST_F(APZCFlingStopTester, FlingStopSlowListener) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+  DoFlingStopWithSlowListener(false);
+}
+
+TEST_F(APZCFlingStopTester, FlingStopPreventDefault) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+  DoFlingStopWithSlowListener(true);
+}
+
+TEST_F(APZCGestureDetectorTester, ShortPress) {
+  MakeApzcUnzoomable();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    // This verifies that the single tap notification is sent after the
+    // touchup is fully processed. The ordering here is important.
+    EXPECT_CALL(check, Call("pre-tap"));
+    EXPECT_CALL(check, Call("post-tap"));
+    EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10),
+                                0, apzc->GetGuid(), _))
+        .Times(1);
+  }
+
+  check.Call("pre-tap");
+  TapAndCheckStatus(apzc, ScreenIntPoint(10, 10),
+                    TimeDuration::FromMilliseconds(100));
+  check.Call("post-tap");
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCGestureDetectorTester, MediumPress) {
+  MakeApzcUnzoomable();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    // This verifies that the single tap notification is sent after the
+    // touchup is fully processed. The ordering here is important.
+    EXPECT_CALL(check, Call("pre-tap"));
+    EXPECT_CALL(check, Call("post-tap"));
+    EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10),
+                                0, apzc->GetGuid(), _))
+        .Times(1);
+  }
+
+  check.Call("pre-tap");
+  TapAndCheckStatus(apzc, ScreenIntPoint(10, 10),
+                    TimeDuration::FromMilliseconds(400));
+  check.Call("post-tap");
+
+  apzc->AssertStateIsReset();
+}
+
+class APZCLongPressTester : public APZCGestureDetectorTester {
+ protected:
+  void DoLongPressTest(uint32_t aBehavior) {
+    MakeApzcUnzoomable();
+
+    APZEventResult result =
+        TouchDown(apzc, ScreenIntPoint(10, 10), mcc->Time());
+    EXPECT_EQ(nsEventStatus_eConsumeDoDefault, result.GetStatus());
+    uint64_t blockId = result.mInputBlockId;
+
+    if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+      // SetAllowedTouchBehavior() must be called after sending touch-start.
+      nsTArray<uint32_t> allowedTouchBehaviors;
+      allowedTouchBehaviors.AppendElement(aBehavior);
+      apzc->SetAllowedTouchBehavior(blockId, allowedTouchBehaviors);
+    }
+    // Have content "respond" to the touchstart
+    apzc->ContentReceivedInputBlock(blockId, false);
+
+    MockFunction<void(std::string checkPointName)> check;
+
+    {
+      InSequence s;
+
+      EXPECT_CALL(check, Call("preHandleLongTap"));
+      blockId++;
+      EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap, LayoutDevicePoint(10, 10),
+                                  0, apzc->GetGuid(), blockId))
+          .Times(1);
+      EXPECT_CALL(check, Call("postHandleLongTap"));
+
+      EXPECT_CALL(check, Call("preHandleLongTapUp"));
+      EXPECT_CALL(*mcc,
+                  HandleTap(TapType::eLongTapUp, LayoutDevicePoint(10, 10), 0,
+                            apzc->GetGuid(), _))
+          .Times(1);
+      EXPECT_CALL(check, Call("postHandleLongTapUp"));
+    }
+
+    // Manually invoke the longpress while the touch is currently down.
+    check.Call("preHandleLongTap");
+    mcc->RunThroughDelayedTasks();
+    check.Call("postHandleLongTap");
+
+    // Dispatching the longpress event starts a new touch block, which
+    // needs a new content response and also has a pending timeout task
+    // in the queue. Deal with those here. We do the content response first
+    // with preventDefault=false, and then we run the timeout task which
+    // "loses the race" and does nothing.
+    apzc->ContentReceivedInputBlock(blockId, false);
+    mcc->AdvanceByMillis(1000);
+
+    // Finally, simulate lifting the finger. Since the long-press wasn't
+    // prevent-defaulted, we should get a long-tap-up event.
+    check.Call("preHandleLongTapUp");
+    result = TouchUp(apzc, ScreenIntPoint(10, 10), mcc->Time());
+    mcc->RunThroughDelayedTasks();
+    EXPECT_EQ(nsEventStatus_eConsumeDoDefault, result.GetStatus());
+    check.Call("postHandleLongTapUp");
+
+    apzc->AssertStateIsReset();
+  }
+
+  void DoLongPressPreventDefaultTest(uint32_t aBehavior) {
+    MakeApzcUnzoomable();
+
+    EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(0);
+
+    int touchX = 10, touchStartY = 10, touchEndY = 50;
+
+    APZEventResult result =
+        TouchDown(apzc, ScreenIntPoint(touchX, touchStartY), mcc->Time());
+    EXPECT_EQ(nsEventStatus_eConsumeDoDefault, result.GetStatus());
+    uint64_t blockId = result.mInputBlockId;
+
+    if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+      // SetAllowedTouchBehavior() must be called after sending touch-start.
+      nsTArray<uint32_t> allowedTouchBehaviors;
+      allowedTouchBehaviors.AppendElement(aBehavior);
+      apzc->SetAllowedTouchBehavior(blockId, allowedTouchBehaviors);
+    }
+    // Have content "respond" to the touchstart
+    apzc->ContentReceivedInputBlock(blockId, false);
+
+    MockFunction<void(std::string checkPointName)> check;
+
+    {
+      InSequence s;
+
+      EXPECT_CALL(check, Call("preHandleLongTap"));
+      blockId++;
+      EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap,
+                                  LayoutDevicePoint(touchX, touchStartY), 0,
+                                  apzc->GetGuid(), blockId))
+          .Times(1);
+      EXPECT_CALL(check, Call("postHandleLongTap"));
+    }
+
+    // Manually invoke the longpress while the touch is currently down.
+    check.Call("preHandleLongTap");
+    mcc->RunThroughDelayedTasks();
+    check.Call("postHandleLongTap");
+
+    // There should be a TimeoutContentResponse task in the queue still,
+    // waiting for the response from the longtap event dispatched above.
+    // Send the signal that content has handled the long-tap, and then run
+    // the timeout task (it will be a no-op because the content "wins" the
+    // race. This takes the place of the "contextmenu" event.
+    apzc->ContentReceivedInputBlock(blockId, true);
+    mcc->AdvanceByMillis(1000);
+
+    MultiTouchInput mti =
+        CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, mcc->Time());
+    mti.mTouches.AppendElement(SingleTouchData(
+        0, ParentLayerPoint(touchX, touchEndY), ScreenSize(0, 0), 0, 0));
+    result = apzc->ReceiveInputEvent(mti);
+    EXPECT_EQ(nsEventStatus_eConsumeDoDefault, result.GetStatus());
+
+    EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap,
+                                LayoutDevicePoint(touchX, touchEndY), 0,
+                                apzc->GetGuid(), _))
+        .Times(0);
+    result = TouchUp(apzc, ScreenIntPoint(touchX, touchEndY), mcc->Time());
+    EXPECT_EQ(nsEventStatus_eConsumeDoDefault, result.GetStatus());
+
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+    apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+
+    EXPECT_EQ(ParentLayerPoint(), pointOut);
+    EXPECT_EQ(AsyncTransform(), viewTransformOut);
+
+    apzc->AssertStateIsReset();
+  }
+};
+
+TEST_F(APZCLongPressTester, LongPress) {
+  DoLongPressTest(kDefaultTouchBehavior);
+}
+
+TEST_F(APZCLongPressTester, LongPressPreventDefault) {
+  DoLongPressPreventDefaultTest(kDefaultTouchBehavior);
+}
+
+TEST_F(APZCGestureDetectorTester, DoubleTap) {
+  MakeApzcWaitForMainThread();
+  MakeApzcZoomable();
+
+  apzc->GetFrameMetrics().SetIsRootContent(true);
+
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(0);
+  EXPECT_CALL(*mcc, HandleTap(TapType::eDoubleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(1);
+
+  uint64_t blockIds[2];
+  DoubleTapAndCheckStatus(apzc, ScreenIntPoint(10, 10), &blockIds);
+
+  // responses to the two touchstarts
+  apzc->ContentReceivedInputBlock(blockIds[0], false);
+  apzc->ContentReceivedInputBlock(blockIds[1], false);
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCGestureDetectorTester, DoubleTapNotZoomable) {
+  MakeApzcWaitForMainThread();
+  MakeApzcUnzoomable();
+
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(1);
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSecondTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(1);
+  EXPECT_CALL(*mcc, HandleTap(TapType::eDoubleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(0);
+
+  uint64_t blockIds[2];
+  DoubleTapAndCheckStatus(apzc, ScreenIntPoint(10, 10), &blockIds);
+
+  // responses to the two touchstarts
+  apzc->ContentReceivedInputBlock(blockIds[0], false);
+  apzc->ContentReceivedInputBlock(blockIds[1], false);
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCGestureDetectorTester, DoubleTapPreventDefaultFirstOnly) {
+  MakeApzcWaitForMainThread();
+  MakeApzcZoomable();
+
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(1);
+  EXPECT_CALL(*mcc, HandleTap(TapType::eDoubleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(0);
+
+  uint64_t blockIds[2];
+  DoubleTapAndCheckStatus(apzc, ScreenIntPoint(10, 10), &blockIds);
+
+  // responses to the two touchstarts
+  apzc->ContentReceivedInputBlock(blockIds[0], true);
+  apzc->ContentReceivedInputBlock(blockIds[1], false);
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCGestureDetectorTester, DoubleTapPreventDefaultBoth) {
+  MakeApzcWaitForMainThread();
+  MakeApzcZoomable();
+
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(0);
+  EXPECT_CALL(*mcc, HandleTap(TapType::eDoubleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(0);
+
+  uint64_t blockIds[2];
+  DoubleTapAndCheckStatus(apzc, ScreenIntPoint(10, 10), &blockIds);
+
+  // responses to the two touchstarts
+  apzc->ContentReceivedInputBlock(blockIds[0], true);
+  apzc->ContentReceivedInputBlock(blockIds[1], true);
+
+  apzc->AssertStateIsReset();
+}
+
+// Test for bug 947892
+// We test whether we dispatch tap event when the tap is followed by pinch.
+TEST_F(APZCGestureDetectorTester, TapFollowedByPinch) {
+  MakeApzcZoomable();
+
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(1);
+
+  Tap(apzc, ScreenIntPoint(10, 10), TimeDuration::FromMilliseconds(100));
+
+  int inputId = 0;
+  MultiTouchInput mti;
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(SingleTouchData(inputId, ParentLayerPoint(20, 20),
+                                             ScreenSize(0, 0), 0, 0));
+  mti.mTouches.AppendElement(SingleTouchData(
+      inputId + 1, ParentLayerPoint(10, 10), ScreenSize(0, 0), 0, 0));
+  apzc->ReceiveInputEvent(mti);
+
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_END, mcc->Time());
+  mti.mTouches.AppendElement(SingleTouchData(inputId, ParentLayerPoint(20, 20),
+                                             ScreenSize(0, 0), 0, 0));
+  mti.mTouches.AppendElement(SingleTouchData(
+      inputId + 1, ParentLayerPoint(10, 10), ScreenSize(0, 0), 0, 0));
+  apzc->ReceiveInputEvent(mti);
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCGestureDetectorTester, TapFollowedByMultipleTouches) {
+  MakeApzcZoomable();
+
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(1);
+
+  Tap(apzc, ScreenIntPoint(10, 10), TimeDuration::FromMilliseconds(100));
+
+  int inputId = 0;
+  MultiTouchInput mti;
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(SingleTouchData(inputId, ParentLayerPoint(20, 20),
+                                             ScreenSize(0, 0), 0, 0));
+  apzc->ReceiveInputEvent(mti, Some(nsTArray<uint32_t>{kDefaultTouchBehavior}));
+
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(SingleTouchData(inputId, ParentLayerPoint(20, 20),
+                                             ScreenSize(0, 0), 0, 0));
+  mti.mTouches.AppendElement(SingleTouchData(
+      inputId + 1, ParentLayerPoint(10, 10), ScreenSize(0, 0), 0, 0));
+  apzc->ReceiveInputEvent(mti, Some(nsTArray<uint32_t>{kDefaultTouchBehavior}));
+
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_END, mcc->Time());
+  mti.mTouches.AppendElement(SingleTouchData(inputId, ParentLayerPoint(20, 20),
+                                             ScreenSize(0, 0), 0, 0));
+  mti.mTouches.AppendElement(SingleTouchData(
+      inputId + 1, ParentLayerPoint(10, 10), ScreenSize(0, 0), 0, 0));
+  apzc->ReceiveInputEvent(mti);
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCGestureDetectorTester, LongPressInterruptedByWheel) {
+  // Since we try to allow concurrent input blocks of different types to
+  // co-exist, the wheel block shouldn't interrupt the long-press detection.
+  // But more importantly, this shouldn't crash, which is what it did at one
+  // point in time.
+  EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap, _, _, _, _)).Times(1);
+
+  APZEventResult result = TouchDown(apzc, ScreenIntPoint(10, 10), mcc->Time());
+  uint64_t touchBlockId = result.mInputBlockId;
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(apzc, touchBlockId);
+  }
+  mcc->AdvanceByMillis(10);
+  uint64_t wheelBlockId =
+      Wheel(apzc, ScreenIntPoint(10, 10), ScreenPoint(0, -10), mcc->Time())
+          .mInputBlockId;
+  EXPECT_NE(touchBlockId, wheelBlockId);
+  mcc->AdvanceByMillis(1000);
+}
+
+TEST_F(APZCGestureDetectorTester, TapTimeoutInterruptedByWheel) {
+  // In this test, even though the wheel block comes right after the tap, the
+  // tap should still be dispatched because it completes fully before the wheel
+  // block arrived.
+  EXPECT_CALL(*mcc, HandleTap(TapType::eSingleTap, LayoutDevicePoint(10, 10), 0,
+                              apzc->GetGuid(), _))
+      .Times(1);
+
+  // We make the APZC zoomable so the gesture detector needs to wait to
+  // distinguish between tap and double-tap. During that timeout is when we
+  // insert the wheel event.
+  MakeApzcZoomable();
+
+  uint64_t touchBlockId = 0;
+  Tap(apzc, ScreenIntPoint(10, 10), TimeDuration::FromMilliseconds(100),
+      nullptr, &touchBlockId);
+  mcc->AdvanceByMillis(10);
+  uint64_t wheelBlockId =
+      Wheel(apzc, ScreenIntPoint(10, 10), ScreenPoint(0, -10), mcc->Time())
+          .mInputBlockId;
+  EXPECT_NE(touchBlockId, wheelBlockId);
+  while (mcc->RunThroughDelayedTasks())
+    ;
+}
+
+TEST_F(APZCGestureDetectorTester, LongPressWithInputQueueDelay) {
+  // In this test, we ensure that any time spent waiting in the input queue for
+  // the content response is subtracted from the long-press timeout in the
+  // GestureEventListener. In this test the content response timeout is longer
+  // than the long-press timeout.
+  SCOPED_GFX_PREF_INT("apz.content_response_timeout", 60);
+  SCOPED_GFX_PREF_INT("ui.click_hold_context_menus.delay", 30);
+
+  MakeApzcWaitForMainThread();
+
+  MockFunction<void(std::string checkPointName)> check;
+
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("pre long-tap dispatch"));
+    EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap, LayoutDevicePoint(10, 10), 0,
+                                apzc->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("post long-tap dispatch"));
+  }
+
+  // Touch down
+  APZEventResult result = TouchDown(apzc, ScreenIntPoint(10, 10), mcc->Time());
+  uint64_t touchBlockId = result.mInputBlockId;
+  // Simulate content response after 10ms
+  mcc->AdvanceByMillis(10);
+  apzc->ContentReceivedInputBlock(touchBlockId, false);
+  apzc->SetAllowedTouchBehavior(touchBlockId, {kDefaultTouchBehavior});
+  apzc->ConfirmTarget(touchBlockId);
+  // Ensure long-tap event happens within 20ms after that
+  check.Call("pre long-tap dispatch");
+  mcc->AdvanceByMillis(20);
+  check.Call("post long-tap dispatch");
+}
+
+TEST_F(APZCGestureDetectorTester, LongPressWithInputQueueDelay2) {
+  // Similar to the previous test, except this time we don't simulate the
+  // content response at all, and still expect the long-press to happen on
+  // schedule.
+  SCOPED_GFX_PREF_INT("apz.content_response_timeout", 60);
+  SCOPED_GFX_PREF_INT("ui.click_hold_context_menus.delay", 30);
+
+  MakeApzcWaitForMainThread();
+
+  MockFunction<void(std::string checkPointName)> check;
+
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("pre long-tap dispatch"));
+    EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap, LayoutDevicePoint(10, 10), 0,
+                                apzc->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("post long-tap dispatch"));
+  }
+
+  // Touch down
+  TouchDown(apzc, ScreenIntPoint(10, 10), mcc->Time());
+  // Ensure the long-tap happens within 30ms even though there's no content
+  // response.
+  check.Call("pre long-tap dispatch");
+  mcc->AdvanceByMillis(30);
+  check.Call("post long-tap dispatch");
+}
+
+TEST_F(APZCGestureDetectorTester, LongPressWithInputQueueDelay3) {
+  // Similar to the previous test, except now we have the long-press delay
+  // being longer than the content response timeout.
+  SCOPED_GFX_PREF_INT("apz.content_response_timeout", 30);
+  SCOPED_GFX_PREF_INT("ui.click_hold_context_menus.delay", 60);
+
+  MakeApzcWaitForMainThread();
+
+  MockFunction<void(std::string checkPointName)> check;
+
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("pre long-tap dispatch"));
+    EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap, LayoutDevicePoint(10, 10), 0,
+                                apzc->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("post long-tap dispatch"));
+  }
+
+  // Touch down
+  TouchDown(apzc, ScreenIntPoint(10, 10), mcc->Time());
+  // Ensure the long-tap happens at the 60ms mark even though the input event
+  // waits in the input queue for the full content response timeout of 30ms
+  mcc->AdvanceByMillis(59);
+  check.Call("pre long-tap dispatch");
+  mcc->AdvanceByMillis(1);
+  check.Call("post long-tap dispatch");
+}
diff --git a/gfx/layers/apz/test/gtest/TestHitTesting.cpp b/gfx/layers/apz/test/gtest/TestHitTesting.cpp
new file mode 100644
index 0000000000..04f1e40f5d
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestHitTesting.cpp
@@ -0,0 +1,352 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+
+#include "InputUtils.h"
+
+class APZHitTestingTester : public APZCTreeManagerTester {
+ protected:
+  ScreenToParentLayerMatrix4x4 transformToApzc;
+  ParentLayerToScreenMatrix4x4 transformToGecko;
+
+  already_AddRefed<AsyncPanZoomController> GetTargetAPZC(
+      const ScreenPoint& aPoint) {
+    RefPtr<AsyncPanZoomController> hit =
+        manager->GetTargetAPZC(aPoint).mTargetApzc;
+    if (hit) {
+      transformToApzc = manager->GetScreenToApzcTransform(hit.get());
+      transformToGecko =
+          manager->GetApzcToGeckoTransform(hit.get(), LayoutAndVisual);
+    }
+    return hit.forget();
+  }
+
+ protected:
+  void DisableApzOn(WebRenderLayerScrollData* aLayer) {
+    ModifyFrameMetrics(aLayer, [](ScrollMetadata& aSm, FrameMetrics&) {
+      aSm.SetForceDisableApz(true);
+    });
+  }
+
+  void CreateComplexMultiLayerTree() {
+    const char* treeShape = "x(xx(x)xx(x(x)xx))";
+    // LayerID               0 12 3 45 6 7 89
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 300, 400),    // root(0)
+        LayerIntRect(0, 0, 100, 100),    // layer(1) in top-left
+        LayerIntRect(50, 50, 200, 300),  // layer(2) centered in root(0)
+        LayerIntRect(50, 50, 200,
+                     300),  // layer(3) fully occupying parent layer(2)
+        LayerIntRect(0, 200, 100, 100),  // layer(4) in bottom-left
+        LayerIntRect(200, 0, 100,
+                     400),  // layer(5) along the right 100px of root(0)
+        LayerIntRect(200, 0, 100, 200),  // layer(6) taking up the top
+                                         // half of parent layer(5)
+        LayerIntRect(200, 0, 100,
+                     200),  // layer(7) fully occupying parent layer(6)
+        LayerIntRect(200, 200, 100,
+                     100),  // layer(8) in bottom-right (below (6))
+        LayerIntRect(200, 300, 100,
+                     100),  // layer(9) in bottom-right (below (8))
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID);
+    SetScrollableFrameMetrics(layers[2], ScrollableLayerGuid::START_SCROLL_ID);
+    SetScrollableFrameMetrics(layers[4],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1);
+    SetScrollableFrameMetrics(layers[6],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1);
+    SetScrollableFrameMetrics(layers[7],
+                              ScrollableLayerGuid::START_SCROLL_ID + 2);
+    SetScrollableFrameMetrics(layers[8],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1);
+    SetScrollableFrameMetrics(layers[9],
+                              ScrollableLayerGuid::START_SCROLL_ID + 3);
+  }
+
+  void CreateBug1148350LayerTree() {
+    const char* treeShape = "x(x)";
+    // LayerID               0 1
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 200, 200),
+        LayerIntRect(0, 0, 200, 200),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID);
+  }
+};
+
+TEST_F(APZHitTestingTester, ComplexMultiLayerTree) {
+  CreateComplexMultiLayerTree();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  /* The layer tree looks like this:
+
+                0
+        |----|--+--|----|
+        1    2     4    5
+             |         /|\
+             3        6 8 9
+                      |
+                      7
+
+     Layers 1,2 have the same APZC
+     Layers 4,6,8 have the same APZC
+     Layer 7 has an APZC
+     Layer 9 has an APZC
+  */
+
+  TestAsyncPanZoomController* nullAPZC = nullptr;
+  // Ensure all the scrollable layers have an APZC
+
+  EXPECT_FALSE(HasScrollableFrameMetrics(layers[0]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[1]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[2]));
+  EXPECT_FALSE(HasScrollableFrameMetrics(layers[3]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[4]));
+  EXPECT_FALSE(HasScrollableFrameMetrics(layers[5]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[6]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[7]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[8]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[9]));
+  // Ensure those that scroll together have the same APZCs
+  EXPECT_EQ(ApzcOf(layers[1]), ApzcOf(layers[2]));
+  EXPECT_EQ(ApzcOf(layers[4]), ApzcOf(layers[6]));
+  EXPECT_EQ(ApzcOf(layers[8]), ApzcOf(layers[6]));
+  // Ensure those that don't scroll together have different APZCs
+  EXPECT_NE(ApzcOf(layers[1]), ApzcOf(layers[4]));
+  EXPECT_NE(ApzcOf(layers[1]), ApzcOf(layers[7]));
+  EXPECT_NE(ApzcOf(layers[1]), ApzcOf(layers[9]));
+  EXPECT_NE(ApzcOf(layers[4]), ApzcOf(layers[7]));
+  EXPECT_NE(ApzcOf(layers[4]), ApzcOf(layers[9]));
+  EXPECT_NE(ApzcOf(layers[7]), ApzcOf(layers[9]));
+  // Ensure the APZC parent chains are set up correctly
+  TestAsyncPanZoomController* layers1_2 = ApzcOf(layers[1]);
+  TestAsyncPanZoomController* layers4_6_8 = ApzcOf(layers[4]);
+  TestAsyncPanZoomController* layer7 = ApzcOf(layers[7]);
+  TestAsyncPanZoomController* layer9 = ApzcOf(layers[9]);
+  EXPECT_EQ(nullptr, layers1_2->GetParent());
+  EXPECT_EQ(nullptr, layers4_6_8->GetParent());
+  EXPECT_EQ(layers4_6_8, layer7->GetParent());
+  EXPECT_EQ(nullptr, layer9->GetParent());
+  // Ensure the hit-testing tree looks like the layer tree
+  RefPtr<HitTestingTreeNode> root = manager->GetRootNode();
+  RefPtr<HitTestingTreeNode> node5 = root->GetLastChild();
+  RefPtr<HitTestingTreeNode> node4 = node5->GetPrevSibling();
+  RefPtr<HitTestingTreeNode> node2 = node4->GetPrevSibling();
+  RefPtr<HitTestingTreeNode> node1 = node2->GetPrevSibling();
+  RefPtr<HitTestingTreeNode> node3 = node2->GetLastChild();
+  RefPtr<HitTestingTreeNode> node9 = node5->GetLastChild();
+  RefPtr<HitTestingTreeNode> node8 = node9->GetPrevSibling();
+  RefPtr<HitTestingTreeNode> node6 = node8->GetPrevSibling();
+  RefPtr<HitTestingTreeNode> node7 = node6->GetLastChild();
+  EXPECT_EQ(nullptr, node1->GetPrevSibling());
+  EXPECT_EQ(nullptr, node3->GetPrevSibling());
+  EXPECT_EQ(nullptr, node6->GetPrevSibling());
+  EXPECT_EQ(nullptr, node7->GetPrevSibling());
+  EXPECT_EQ(nullptr, node1->GetLastChild());
+  EXPECT_EQ(nullptr, node3->GetLastChild());
+  EXPECT_EQ(nullptr, node4->GetLastChild());
+  EXPECT_EQ(nullptr, node7->GetLastChild());
+  EXPECT_EQ(nullptr, node8->GetLastChild());
+  EXPECT_EQ(nullptr, node9->GetLastChild());
+
+  // Assertions about hit-testing have been ported to mochitest,
+  // in helper_hittest_bug1730606-4.html.
+}
+
+TEST_F(APZHitTestingTester, TestRepaintFlushOnNewInputBlock) {
+  // The main purpose of this test is to verify that touch-start events (or
+  // anything that starts a new input block) don't ever get untransformed. This
+  // should always hold because the APZ code should flush repaints when we start
+  // a new input block and the transform to gecko space should be empty.
+
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  RefPtr<TestAsyncPanZoomController> apzcroot = ApzcOf(root);
+
+  // At this point, the following holds (all coordinates in screen pixels):
+  // layers[0] has content from (0,0)-(500,500), clipped by composition bounds
+  // (0,0)-(200,200)
+
+  MockFunction<void(std::string checkPointName)> check;
+
+  {
+    InSequence s;
+
+    EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(AtLeast(1));
+    EXPECT_CALL(check, Call("post-first-touch-start"));
+    EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(AtLeast(1));
+    EXPECT_CALL(check, Call("post-second-fling"));
+    EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(AtLeast(1));
+    EXPECT_CALL(check, Call("post-second-touch-start"));
+  }
+
+  // This first pan will move the APZC by 50 pixels, and dispatch a paint
+  // request.
+  Pan(apzcroot, 100, 50, PanOptions::NoFling);
+
+  // Verify that a touch start doesn't get untransformed
+  ScreenIntPoint touchPoint(50, 50);
+  MultiTouchInput mti =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(
+      SingleTouchData(0, touchPoint, ScreenSize(0, 0), 0, 0));
+
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault,
+            manager->ReceiveInputEvent(mti).GetStatus());
+  EXPECT_EQ(touchPoint, mti.mTouches[0].mScreenPoint);
+  check.Call("post-first-touch-start");
+
+  // Send a touchend to clear state
+  mti.mType = MultiTouchInput::MULTITOUCH_END;
+  manager->ReceiveInputEvent(mti);
+
+  mcc->AdvanceByMillis(1000);
+
+  // Now do two pans. The first of these will dispatch a repaint request, as
+  // above. The second will get stuck in the paint throttler because the first
+  // one doesn't get marked as "completed", so this will result in a non-empty
+  // LD transform. (Note that any outstanding repaint requests from the first
+  // half of this test don't impact this half because we advance the time by 1
+  // second, which will trigger the max-wait-exceeded codepath in the paint
+  // throttler).
+  Pan(apzcroot, 100, 50, PanOptions::NoFling);
+  check.Call("post-second-fling");
+  Pan(apzcroot, 100, 50, PanOptions::NoFling);
+
+  // Ensure that a touch start again doesn't get untransformed by flushing
+  // a repaint
+  mti.mType = MultiTouchInput::MULTITOUCH_START;
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault,
+            manager->ReceiveInputEvent(mti).GetStatus());
+  EXPECT_EQ(touchPoint, mti.mTouches[0].mScreenPoint);
+  check.Call("post-second-touch-start");
+
+  mti.mType = MultiTouchInput::MULTITOUCH_END;
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault,
+            manager->ReceiveInputEvent(mti).GetStatus());
+  EXPECT_EQ(touchPoint, mti.mTouches[0].mScreenPoint);
+}
+
+TEST_F(APZHitTestingTester, TestRepaintFlushOnWheelEvents) {
+  // The purpose of this test is to ensure that wheel events trigger a repaint
+  // flush as per bug 1166871, and that the wheel event untransform is a no-op.
+
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  TestAsyncPanZoomController* apzcroot = ApzcOf(root);
+
+  EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(AtLeast(3));
+  ScreenPoint origin(100, 50);
+  for (int i = 0; i < 3; i++) {
+    ScrollWheelInput swi(mcc->Time(), 0, ScrollWheelInput::SCROLLMODE_INSTANT,
+                         ScrollWheelInput::SCROLLDELTA_PIXEL, origin, 0, 10,
+                         false, WheelDeltaAdjustmentStrategy::eNone);
+    EXPECT_EQ(nsEventStatus_eConsumeDoDefault,
+              manager->ReceiveInputEvent(swi).GetStatus());
+    EXPECT_EQ(origin, swi.mOrigin);
+
+    AsyncTransform viewTransform;
+    ParentLayerPoint point;
+    apzcroot->SampleContentTransformForFrame(&viewTransform, point);
+    EXPECT_EQ(0, point.x);
+    EXPECT_EQ((i + 1) * 10, point.y);
+    EXPECT_EQ(0, viewTransform.mTranslation.x);
+    EXPECT_EQ((i + 1) * -10, viewTransform.mTranslation.y);
+
+    mcc->AdvanceByMillis(5);
+  }
+}
+
+TEST_F(APZHitTestingTester, TestForceDisableApz) {
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  DisableApzOn(root);
+  TestAsyncPanZoomController* apzcroot = ApzcOf(root);
+
+  ScreenPoint origin(100, 50);
+  ScrollWheelInput swi(mcc->Time(), 0, ScrollWheelInput::SCROLLMODE_INSTANT,
+                       ScrollWheelInput::SCROLLDELTA_PIXEL, origin, 0, 10,
+                       false, WheelDeltaAdjustmentStrategy::eNone);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault,
+            manager->ReceiveInputEvent(swi).GetStatus());
+  EXPECT_EQ(origin, swi.mOrigin);
+
+  AsyncTransform viewTransform;
+  ParentLayerPoint point;
+  apzcroot->SampleContentTransformForFrame(&viewTransform, point);
+  // Since APZ is force-disabled, we expect to see the async transform via
+  // the NORMAL AsyncMode, but not via the RESPECT_FORCE_DISABLE AsyncMode.
+  EXPECT_EQ(0, point.x);
+  EXPECT_EQ(10, point.y);
+  EXPECT_EQ(0, viewTransform.mTranslation.x);
+  EXPECT_EQ(-10, viewTransform.mTranslation.y);
+  viewTransform = apzcroot->GetCurrentAsyncTransform(
+      AsyncPanZoomController::eForCompositing);
+  point = apzcroot->GetCurrentAsyncScrollOffset(
+      AsyncPanZoomController::eForCompositing);
+  EXPECT_EQ(0, point.x);
+  EXPECT_EQ(0, point.y);
+  EXPECT_EQ(0, viewTransform.mTranslation.x);
+  EXPECT_EQ(0, viewTransform.mTranslation.y);
+
+  mcc->AdvanceByMillis(10);
+
+  // With untransforming events we should get normal behaviour (in this case,
+  // no noticeable untransform, because the repaint request already got
+  // flushed).
+  swi = ScrollWheelInput(mcc->Time(), 0, ScrollWheelInput::SCROLLMODE_INSTANT,
+                         ScrollWheelInput::SCROLLDELTA_PIXEL, origin, 0, 0,
+                         false, WheelDeltaAdjustmentStrategy::eNone);
+  EXPECT_EQ(nsEventStatus_eConsumeDoDefault,
+            manager->ReceiveInputEvent(swi).GetStatus());
+  EXPECT_EQ(origin, swi.mOrigin);
+}
+
+TEST_F(APZHitTestingTester, Bug1148350) {
+  CreateBug1148350LayerTree();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(*mcc,
+                HandleTap(TapType::eSingleTap, LayoutDevicePoint(100, 100), 0,
+                          ApzcOf(layers[1])->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Tapped without transform"));
+    EXPECT_CALL(*mcc,
+                HandleTap(TapType::eSingleTap, LayoutDevicePoint(100, 100), 0,
+                          ApzcOf(layers[1])->GetGuid(), _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Tapped with interleaved transform"));
+  }
+
+  Tap(manager, ScreenIntPoint(100, 100), TimeDuration::FromMilliseconds(100));
+  mcc->RunThroughDelayedTasks();
+  check.Call("Tapped without transform");
+
+  uint64_t blockId =
+      TouchDown(manager, ScreenIntPoint(100, 100), mcc->Time()).mInputBlockId;
+  SetDefaultAllowedTouchBehavior(manager, blockId);
+  mcc->AdvanceByMillis(100);
+
+  layers[0]->SetVisibleRegion(LayerIntRegion(LayerIntRect(0, 50, 200, 150)));
+  layers[0]->SetTransform(Matrix4x4::Translation(0, 50, 0));
+  UpdateHitTestingTree();
+
+  TouchUp(manager, ScreenIntPoint(100, 100), mcc->Time());
+  mcc->RunThroughDelayedTasks();
+  check.Call("Tapped with interleaved transform");
+}
diff --git a/gfx/layers/apz/test/gtest/TestInputQueue.cpp b/gfx/layers/apz/test/gtest/TestInputQueue.cpp
new file mode 100644
index 0000000000..6e47340da5
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestInputQueue.cpp
@@ -0,0 +1,45 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+
+// Test of scenario described in bug 1269067 - that a continuing mouse drag
+// doesn't interrupt a wheel scrolling animation
+TEST_F(APZCTreeManagerTester, WheelInterruptedByMouseDrag) {
+  // Set up a scrollable layer
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+
+  // First start the mouse drag
+  uint64_t dragBlockId =
+      MouseDown(apzc, ScreenIntPoint(5, 5), mcc->Time()).mInputBlockId;
+  uint64_t tmpBlockId =
+      MouseMove(apzc, ScreenIntPoint(6, 6), mcc->Time()).mInputBlockId;
+  EXPECT_EQ(dragBlockId, tmpBlockId);
+
+  // Insert the wheel event, check that it has a new block id
+  uint64_t wheelBlockId =
+      SmoothWheel(apzc, ScreenIntPoint(6, 6), ScreenPoint(0, 1), mcc->Time())
+          .mInputBlockId;
+  EXPECT_NE(dragBlockId, wheelBlockId);
+
+  // Continue the drag, check that the block id is the same as before
+  tmpBlockId = MouseMove(apzc, ScreenIntPoint(7, 5), mcc->Time()).mInputBlockId;
+  EXPECT_EQ(dragBlockId, tmpBlockId);
+
+  // Finish the wheel animation
+  apzc->AdvanceAnimationsUntilEnd();
+
+  // Check that it scrolled
+  ParentLayerPoint scroll =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  EXPECT_EQ(scroll.x, 0);
+  EXPECT_EQ(scroll.y, 10);  // We scrolled 1 "line" or 10 pixels
+}
diff --git a/gfx/layers/apz/test/gtest/TestOverscroll.cpp b/gfx/layers/apz/test/gtest/TestOverscroll.cpp
new file mode 100644
index 0000000000..10327871fb
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestOverscroll.cpp
@@ -0,0 +1,1991 @@
+/* -*- 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 "APZCBasicTester.h"
+#include "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "mozilla/layers/WebRenderScrollDataWrapper.h"
+
+#include "InputUtils.h"
+
+class APZCOverscrollTester : public APZCBasicTester {
+ public:
+  explicit APZCOverscrollTester(
+      AsyncPanZoomController::GestureBehavior aGestureBehavior =
+          AsyncPanZoomController::DEFAULT_GESTURES)
+      : APZCBasicTester(aGestureBehavior) {}
+
+ protected:
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+
+  void TestOverscroll() {
+    // Pan sufficiently to hit overscroll behavior
+    PanIntoOverscroll();
+
+    // Check that we recover from overscroll via an animation.
+    ParentLayerPoint expectedScrollOffset(0, GetScrollRange().YMost());
+    SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+  }
+
+  void PanIntoOverscroll() {
+    int touchStart = 500;
+    int touchEnd = 10;
+    Pan(apzc, touchStart, touchEnd);
+    EXPECT_TRUE(apzc->IsOverscrolled());
+  }
+
+  /**
+   * Sample animations until we recover from overscroll.
+   * @param aExpectedScrollOffset the expected reported scroll offset
+   *                              throughout the animation
+   */
+  void SampleAnimationUntilRecoveredFromOverscroll(
+      const ParentLayerPoint& aExpectedScrollOffset) {
+    const TimeDuration increment = TimeDuration::FromMilliseconds(1);
+    bool recoveredFromOverscroll = false;
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+    while (apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut)) {
+      // The reported scroll offset should be the same throughout.
+      EXPECT_EQ(aExpectedScrollOffset, pointOut);
+
+      // Trigger computation of the overscroll tranform, to make sure
+      // no assetions fire during the calculation.
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+
+      if (!apzc->IsOverscrolled()) {
+        recoveredFromOverscroll = true;
+      }
+
+      mcc->AdvanceBy(increment);
+    }
+    EXPECT_TRUE(recoveredFromOverscroll);
+    apzc->AssertStateIsReset();
+  }
+
+  ScrollableLayerGuid CreateSimpleRootScrollableForWebRender() {
+    ScrollableLayerGuid guid;
+    guid.mScrollId = ScrollableLayerGuid::START_SCROLL_ID;
+    guid.mLayersId = LayersId{0};
+
+    ScrollMetadata metadata;
+    FrameMetrics& metrics = metadata.GetMetrics();
+    metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+    metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+    metrics.SetScrollId(guid.mScrollId);
+    metadata.SetIsLayersIdRoot(true);
+
+    WebRenderLayerScrollData rootLayerScrollData;
+    rootLayerScrollData.InitializeRoot(0);
+    WebRenderScrollData scrollData;
+    rootLayerScrollData.AppendScrollMetadata(scrollData, metadata);
+    scrollData.AddLayerData(std::move(rootLayerScrollData));
+
+    registration = MakeUnique<ScopedLayerTreeRegistration>(guid.mLayersId, mcc);
+    tm->UpdateHitTestingTree(WebRenderScrollDataWrapper(*updater, &scrollData),
+                             false, guid.mLayersId, 0);
+    return guid;
+  }
+};
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, FlingIntoOverscroll) {
+  // Enable overscrolling.
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  // Scroll down by 25 px. Don't fling for simplicity.
+  Pan(apzc, 50, 25, PanOptions::NoFling);
+
+  // Now scroll back up by 20px, this time flinging after.
+  // The fling should cover the remaining 5 px of room to scroll, then
+  // go into overscroll, and finally snap-back to recover from overscroll.
+  Pan(apzc, 25, 45);
+  const TimeDuration increment = TimeDuration::FromMilliseconds(1);
+  bool reachedOverscroll = false;
+  bool recoveredFromOverscroll = false;
+  while (apzc->AdvanceAnimations(mcc->GetSampleTime())) {
+    if (!reachedOverscroll && apzc->IsOverscrolled()) {
+      reachedOverscroll = true;
+    }
+    if (reachedOverscroll && !apzc->IsOverscrolled()) {
+      recoveredFromOverscroll = true;
+    }
+    mcc->AdvanceBy(increment);
+  }
+  EXPECT_TRUE(reachedOverscroll);
+  EXPECT_TRUE(recoveredFromOverscroll);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, OverScrollPanning) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  TestOverscroll();
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+// Tests that an overscroll animation doesn't trigger an assertion failure
+// in the case where a sample has a velocity of zero.
+TEST_F(APZCOverscrollTester, OverScroll_Bug1152051a) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Doctor the prefs to make the velocity zero at the end of the first sample.
+
+  // This ensures our incoming velocity to the overscroll animation is
+  // a round(ish) number, 4.9 (that being the distance of the pan before
+  // overscroll, which is 500 - 10 = 490 pixels, divided by the duration of
+  // the pan, which is 100 ms).
+  SCOPED_GFX_PREF_FLOAT("apz.fling_friction", 0);
+
+  TestOverscroll();
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+// Tests that ending an overscroll animation doesn't leave around state that
+// confuses the next overscroll animation.
+TEST_F(APZCOverscrollTester, OverScroll_Bug1152051b) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+  SCOPED_GFX_PREF_FLOAT("apz.overscroll.stop_distance_threshold", 0.1f);
+
+  // Pan sufficiently to hit overscroll behavior
+  PanIntoOverscroll();
+
+  // Sample animations once, to give the fling animation started on touch-up
+  // a chance to realize it's overscrolled, and schedule a call to
+  // HandleFlingOverscroll().
+  SampleAnimationOnce();
+
+  // This advances the time and runs the HandleFlingOverscroll task scheduled in
+  // the previous call, which starts an overscroll animation. It then samples
+  // the overscroll animation once, to get it to initialize the first overscroll
+  // sample.
+  SampleAnimationOnce();
+
+  // Do a touch-down to cancel the overscroll animation, and then a touch-up
+  // to schedule a new one since we're still overscrolled. We don't pan because
+  // panning can trigger functions that clear the overscroll animation state
+  // in other ways.
+  APZEventResult result = TouchDown(apzc, ScreenIntPoint(10, 10), mcc->Time());
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(apzc, result.mInputBlockId);
+  }
+  TouchUp(apzc, ScreenIntPoint(10, 10), mcc->Time());
+
+  // Sample the second overscroll animation to its end.
+  // If the ending of the first overscroll animation fails to clear state
+  // properly, this will assert.
+  ParentLayerPoint expectedScrollOffset(0, GetScrollRange().YMost());
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+// Tests that the page doesn't get stuck in an
+// overscroll animation after a low-velocity pan.
+TEST_F(APZCOverscrollTester, OverScrollAfterLowVelocityPan_Bug1343775) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Pan into overscroll with a velocity less than the
+  // apz.fling_min_velocity_threshold preference.
+  Pan(apzc, 10, 30);
+
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  apzc->AdvanceAnimationsUntilEnd();
+
+  // Check that we recovered from overscroll.
+  EXPECT_FALSE(apzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, OverScrollAbort) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Pan sufficiently to hit overscroll behavior
+  int touchStart = 500;
+  int touchEnd = 10;
+  Pan(apzc, touchStart, touchEnd);
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  ParentLayerPoint pointOut;
+  AsyncTransform viewTransformOut;
+
+  // This sample call will run to the end of the fling animation
+  // and will schedule the overscroll animation.
+  apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut,
+                                       TimeDuration::FromMilliseconds(10000));
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // At this point, we have an active overscroll animation.
+  // Check that cancelling the animation clears the overscroll.
+  apzc->CancelAnimation();
+  EXPECT_FALSE(apzc->IsOverscrolled());
+  apzc->AssertStateIsReset();
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, OverScrollPanningAbort) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Pan sufficiently to hit overscroll behaviour. Keep the finger down so
+  // the pan does not end.
+  int touchStart = 500;
+  int touchEnd = 10;
+  Pan(apzc, touchStart, touchEnd, PanOptions::KeepFingerDown);
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Check that calling CancelAnimation() while the user is still panning
+  // (and thus no fling or snap-back animation has had a chance to start)
+  // clears the overscroll.
+  apzc->CancelAnimation();
+  EXPECT_FALSE(apzc->IsOverscrolled());
+  apzc->AssertStateIsReset();
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Maybe fails on Android
+TEST_F(APZCOverscrollTester, OverscrollByVerticalPanGestures) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Check that we recover from overscroll via an animation.
+  ParentLayerPoint expectedScrollOffset(0, 0);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, StuckInOverscroll_Bug1767337) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Send two PANGESTURE_END in a row, to see if the second one gets us
+  // stuck in overscroll.
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time(), MODIFIER_NONE, true);
+  SampleAnimationOnce();
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time(), MODIFIER_NONE, true);
+
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Check that we recover from overscroll via an animation.
+  ParentLayerPoint expectedScrollOffset(0, 0);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, OverscrollByVerticalAndHorizontalPanGestures) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-10, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, 0), mcc->Time());
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Check that we recover from overscroll via an animation.
+  ParentLayerPoint expectedScrollOffset(0, 0);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, OverscrollByPanMomentumGestures) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Make sure we are not yet in overscrolled region.
+  EXPECT_TRUE(!apzc->IsOverscrolled());
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 200), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 100), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Check that we recover from overscroll via an animation.
+  ParentLayerPoint expectedScrollOffset(0, GetScrollRange().YMost());
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, IgnoreMomemtumDuringOverscroll) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  float yMost = GetScrollRange().YMost();
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, yMost / 10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, yMost), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, yMost / 10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Make sure we've started an overscroll animation.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+
+  // And check the overscrolled transform value before/after calling PanGesture
+  // to make sure the overscroll amount isn't affected by momentum events.
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  AsyncTransformComponentMatrix overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_EQ(overscrolledTransform, apzc->GetOverscrollTransform(
+                                       AsyncPanZoomController::eForHitTesting));
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 200), mcc->Time());
+  EXPECT_EQ(overscrolledTransform, apzc->GetOverscrollTransform(
+                                       AsyncPanZoomController::eForHitTesting));
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 100), mcc->Time());
+  EXPECT_EQ(overscrolledTransform, apzc->GetOverscrollTransform(
+                                       AsyncPanZoomController::eForHitTesting));
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 2), mcc->Time());
+  EXPECT_EQ(overscrolledTransform, apzc->GetOverscrollTransform(
+                                       AsyncPanZoomController::eForHitTesting));
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_EQ(overscrolledTransform, apzc->GetOverscrollTransform(
+                                       AsyncPanZoomController::eForHitTesting));
+
+  // Check that we've recovered from overscroll via an animation.
+  ParentLayerPoint expectedScrollOffset(0, GetScrollRange().YMost());
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, VerticalOnlyOverscroll) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Make the content scrollable only vertically.
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  apzc->SetFrameMetrics(metrics);
+
+  // Scroll up into overscroll a bit.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-10, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+  // Now it's overscrolled.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  AsyncTransformComponentMatrix overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  // The overscroll shouldn't happen horizontally.
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  // Happens only vertically.
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  // Send pan momentum events including horizontal bits.
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(-10, -100), mcc->Time());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  // The overscroll shouldn't happen horizontally.
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(-5, -50), mcc->Time());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, -2), mcc->Time());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  // Check that we recover from overscroll via an animation.
+  ParentLayerPoint expectedScrollOffset(0, 0);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, VerticalOnlyOverscrollByPanMomentum) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Make the content scrollable only vertically.
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  // Scrolls the content down a bit.
+  metrics.SetVisualScrollOffset(CSSPoint(0, 50));
+  apzc->SetFrameMetrics(metrics);
+
+  // Scroll up a bit where overscroll will not happen.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Make sure it's not yet overscrolled.
+  EXPECT_TRUE(!apzc->IsOverscrolled());
+
+  // Send pan momentum events including horizontal bits.
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(-10, -100), mcc->Time());
+  // Now it's overscrolled.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  AsyncTransformComponentMatrix overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  // But the overscroll shouldn't happen horizontally.
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  // Happens only vertically.
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(-5, -50), mcc->Time());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, -2), mcc->Time());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  overscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_TRUE(overscrolledTransform._41 == 0);
+  EXPECT_TRUE(overscrolledTransform._42 != 0);
+
+  // Check that we recover from overscroll via an animation.
+  ParentLayerPoint expectedScrollOffset(0, 0);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, DisallowOverscrollInSingleLineTextControl) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Create a horizontal scrollable frame with `vertical disregarded direction`.
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 10));
+  metrics.SetScrollableRect(CSSRect(0, 0, 1000, 10));
+  apzc->SetFrameMetrics(metrics);
+  metadata.SetDisregardedDirection(Some(ScrollDirection::eVertical));
+  apzc->NotifyLayersUpdated(metadata, /*aIsFirstPaint=*/false,
+                            /*aThisLayerTreeUpdated=*/true);
+
+  // Try to overscroll up and left with pan gestures.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 5),
+             ScreenPoint(-2, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 5),
+             ScreenPoint(-10, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 5),
+             ScreenPoint(-2, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 5),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // No overscrolling should happen.
+  EXPECT_TRUE(!apzc->IsOverscrolled());
+
+  // Send pan momentum events too.
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 5), ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 5), ScreenPoint(-100, -100), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 5), ScreenPoint(-50, -50), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 5), ScreenPoint(-2, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 5), ScreenPoint(0, 0), mcc->Time());
+  // No overscrolling should happen either.
+  EXPECT_TRUE(!apzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Maybe fails on Android
+// Tests that horizontal overscroll animation keeps running with vertical
+// pan momentum scrolling.
+TEST_F(APZCOverscrollTester,
+       HorizontalOverscrollAnimationWithVerticalPanMomentumScrolling) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 1000, 5000));
+  apzc->SetFrameMetrics(metrics);
+
+  // Try to overscroll left with pan gestures.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-10, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Make sure we've started an overscroll animation.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  AsyncTransformComponentMatrix initialOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+
+  // Send lengthy downward momentums to make sure the overscroll animation
+  // doesn't clobber the momentums scrolling.
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll amount on X axis has started being managed by the overscroll
+  // animation.
+  AsyncTransformComponentMatrix currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_NE(initialOverscrolledTransform._41, currentOverscrolledTransform._41);
+  // There is no overscroll on Y axis.
+  EXPECT_EQ(currentOverscrolledTransform._42, 0);
+  ParentLayerPoint scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  // The scroll offset shouldn't be changed by the overscroll animation.
+  EXPECT_EQ(scrollOffset.y, 0);
+
+  // Simple gesture on the Y axis to ensure that we can send a vertical
+  // momentum scroll
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  ParentLayerPoint offsetAfterPan =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on both axes shouldn't be changed by this pan
+  // momentum start event since the displacement is zero.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  EXPECT_EQ(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll amount should be managed by the overscroll animation.
+  EXPECT_NE(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  // Not yet started scrolling.
+  EXPECT_EQ(scrollOffset.y, offsetAfterPan.y);
+  EXPECT_EQ(scrollOffset.x, 0);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+
+  // Send a long pan momentum.
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 200), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on X axis shouldn't be changed by this momentum pan.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // Now it started scrolling vertically.
+  scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  EXPECT_GT(scrollOffset.y, 0);
+  EXPECT_EQ(scrollOffset.x, 0);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll on X axis keeps being managed by the overscroll animation.
+  EXPECT_NE(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // The scroll offset on Y axis shouldn't be changed by the overscroll
+  // animation.
+  EXPECT_EQ(scrollOffset.y, apzc->GetCurrentAsyncScrollOffset(
+                                    AsyncPanZoomController::eForHitTesting)
+                                .y);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 100), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on X axis shouldn't be changed by this momentum pan.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // Scrolling keeps going by momentum.
+  EXPECT_GT(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      scrollOffset.y);
+
+  scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 10), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // Scrolling keeps going by momentum.
+  EXPECT_GT(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      scrollOffset.y);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // This momentum event doesn't change the scroll offset since its
+  // displacement is zero.
+  EXPECT_EQ(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      scrollOffset.y);
+
+  // Check that we recover from the horizontal overscroll via the animation.
+  ParentLayerPoint expectedScrollOffset(0, scrollOffset.y);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Maybe fails on Android
+// Similar to above
+// HorizontalOverscrollAnimationWithVerticalPanMomentumScrolling,
+// but having OverscrollAnimation on both axes initially.
+TEST_F(APZCOverscrollTester,
+       BothAxesOverscrollAnimationWithPanMomentumScrolling) {
+  // TODO: This test currently requires gestures that cause movement on both
+  // axis, which excludes DOMINANT_AXIS locking mode. The gestures should be
+  // broken up into multiple gestures to cause the overscroll.
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 2);
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 1000, 5000));
+  apzc->SetFrameMetrics(metrics);
+
+  // Try to overscroll up and left with pan gestures.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-10, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Make sure we've started an overscroll animation.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  AsyncTransformComponentMatrix initialOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+
+  // Send lengthy downward momentums to make sure the overscroll animation
+  // doesn't clobber the momentums scrolling.
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll amount has started being managed by the overscroll
+  // animation.
+  AsyncTransformComponentMatrix currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_NE(initialOverscrolledTransform._41, currentOverscrolledTransform._41);
+  EXPECT_NE(initialOverscrolledTransform._42, currentOverscrolledTransform._42);
+
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on both axes shouldn't be changed by this pan
+  // momentum start event since the displacement is zero.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  EXPECT_EQ(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // Still being managed by the overscroll animation.
+  EXPECT_NE(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  EXPECT_NE(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  // Send a long pan momentum.
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 200), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on X axis shouldn't be changed by this momentum pan.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // But now the overscroll amount on Y axis should be changed by this momentum
+  // pan.
+  EXPECT_NE(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+  // Actually it's no longer overscrolled.
+  EXPECT_EQ(
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42,
+      0);
+
+  ParentLayerPoint currentScrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  // Now it started scrolling.
+  EXPECT_GT(currentScrollOffset.y, 0);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll on X axis keeps being managed by the overscroll animation.
+  EXPECT_NE(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // But the overscroll on Y axis is no longer affected by the overscroll
+  // animation.
+  EXPECT_EQ(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+  // The scroll offset on Y axis shouldn't be changed by the overscroll
+  // animation.
+  EXPECT_EQ(
+      currentScrollOffset.y,
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  currentScrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 100), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on X axis shouldn't be changed by this momentum pan.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // Keeping no overscrolling on Y axis.
+  EXPECT_EQ(
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42,
+      0);
+  // Scrolling keeps going by momentum.
+  EXPECT_GT(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      currentScrollOffset.y);
+
+  currentScrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 10), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // Keeping no overscrolling on Y axis.
+  EXPECT_EQ(
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42,
+      0);
+  // Scrolling keeps going by momentum.
+  EXPECT_GT(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      currentScrollOffset.y);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  currentScrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // Keeping no overscrolling on Y axis.
+  EXPECT_EQ(
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42,
+      0);
+  // This momentum event doesn't change the scroll offset since its
+  // displacement is zero.
+  EXPECT_EQ(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      currentScrollOffset.y);
+
+  // Check that we recover from the horizontal overscroll via the animation.
+  ParentLayerPoint expectedScrollOffset(0, currentScrollOffset.y);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Maybe fails on Android
+// This is another variant of
+// HorizontalOverscrollAnimationWithVerticalPanMomentumScrolling. In this test,
+// after a horizontal overscroll animation started, upwards pan moments happen,
+// thus there should be a new vertical overscroll animation in addition to
+// the horizontal one.
+TEST_F(
+    APZCOverscrollTester,
+    VerticalOverscrollAnimationInAdditionToExistingHorizontalOverscrollAnimation) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 1000, 5000));
+  // Scrolls the content 50px down.
+  metrics.SetVisualScrollOffset(CSSPoint(0, 50));
+  apzc->SetFrameMetrics(metrics);
+
+  // Try to overscroll left with pan gestures.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-10, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(-2, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Make sure we've started an overscroll animation.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  AsyncTransformComponentMatrix initialOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+
+  // Send lengthy __upward__ momentums to make sure the overscroll animation
+  // doesn't clobber the momentums scrolling.
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll amount on X axis has started being managed by the overscroll
+  // animation.
+  AsyncTransformComponentMatrix currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  EXPECT_NE(initialOverscrolledTransform._41, currentOverscrolledTransform._41);
+  // There is no overscroll on Y axis.
+  EXPECT_EQ(
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42,
+      0);
+  ParentLayerPoint scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  // The scroll offset shouldn't be changed by the overscroll animation.
+  EXPECT_EQ(scrollOffset.y, 50);
+
+  // Simple gesture on the Y axis to ensure that we can send a vertical
+  // momentum scroll
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  ParentLayerPoint offsetAfterPan =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on both axes shouldn't be changed by this pan
+  // momentum start event since the displacement is zero.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  EXPECT_EQ(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll amount should be managed by the overscroll animation.
+  EXPECT_NE(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  // Not yet started scrolling.
+  EXPECT_EQ(scrollOffset.y, offsetAfterPan.y);
+  EXPECT_EQ(scrollOffset.x, 0);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+
+  // Send a long pan momentum.
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, -200), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on X axis shouldn't be changed by this momentum pan.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // Now it started scrolling vertically.
+  scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  EXPECT_EQ(scrollOffset.y, 0);
+  EXPECT_EQ(scrollOffset.x, 0);
+  // Actually it's also vertically overscrolled.
+  EXPECT_GT(
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42,
+      0);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // The overscroll on X axis keeps being managed by the overscroll animation.
+  EXPECT_NE(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // The overscroll on Y Axis hasn't been changed by the overscroll animation at
+  // this moment, sine the last displacement was consumed in the last pan
+  // momentum.
+  EXPECT_EQ(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, -100), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on X axis shouldn't be changed by this momentum pan.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // Now the overscroll amount on Y axis shouldn't be changed by this momentum
+  // pan either.
+  EXPECT_EQ(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  EXPECT_NE(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  // And now the overscroll on Y Axis should be also managed by the overscroll
+  // animation.
+  EXPECT_NE(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, -10), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+  // The overscroll amount on both axes shouldn't be changed by momentum event.
+  EXPECT_EQ(
+      currentOverscrolledTransform._41,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._41);
+  EXPECT_EQ(
+      currentOverscrolledTransform._42,
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting)._42);
+
+  currentOverscrolledTransform =
+      apzc->GetOverscrollTransform(AsyncPanZoomController::eForHitTesting);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, apzc,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+
+  // Check that we recover from the horizontal overscroll via the animation.
+  ParentLayerPoint expectedScrollOffset(0, 0);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTester, OverscrollByPanGesturesInterruptedByReflowZoom) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+  SCOPED_GFX_PREF_INT("mousewheel.with_control.action", 3);  // reflow zoom.
+
+  // A sanity check that pan gestures with ctrl modifier will not be handled by
+  // APZ.
+  PanGestureInput panInput(PanGestureInput::PANGESTURE_START, mcc->Time(),
+                           ScreenIntPoint(5, 5), ScreenPoint(0, -2),
+                           MODIFIER_CONTROL);
+  WidgetWheelEvent wheelEvent = panInput.ToWidgetEvent(nullptr);
+  EXPECT_FALSE(APZInputBridge::ActionForWheelEvent(&wheelEvent).isSome());
+
+  ScrollableLayerGuid rootGuid = CreateSimpleRootScrollableForWebRender();
+  RefPtr<AsyncPanZoomController> apzc =
+      tm->GetTargetAPZC(rootGuid.mLayersId, rootGuid.mScrollId);
+
+  PanGesture(PanGestureInput::PANGESTURE_START, tm, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  PanGesture(PanGestureInput::PANGESTURE_PAN, tm, ScreenIntPoint(50, 80),
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Make sure overscrolling has started.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Press ctrl until PANGESTURE_END.
+  PanGestureWithModifiers(PanGestureInput::PANGESTURE_PAN, MODIFIER_CONTROL, tm,
+                          ScreenIntPoint(50, 80), ScreenPoint(0, -2),
+                          mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  // At this moment (i.e. PANGESTURE_PAN), still in overscrolling state.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  PanGestureWithModifiers(PanGestureInput::PANGESTURE_END, MODIFIER_CONTROL, tm,
+                          ScreenIntPoint(50, 80), ScreenPoint(0, 0),
+                          mcc->Time());
+  // The overscrolling state should have been restored.
+  EXPECT_TRUE(!apzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTester, SmoothTransitionFromPanToAnimation) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  // Start scrolled down to y=500px.
+  metrics.SetVisualScrollOffset(CSSPoint(0, 500));
+  apzc->SetFrameMetrics(metrics);
+
+  int frameLength = 10;    // milliseconds; 10 to keep the math simple
+  float panVelocity = 10;  // pixels per millisecond
+  int panPixelsPerFrame = frameLength * panVelocity;  // 100 pixels per frame
+
+  ScreenIntPoint panPoint(50, 50);
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, panPoint,
+             ScreenPoint(0, -1), mcc->Time());
+  // Pan up for 6 frames at 100 pixels per frame. This should reduce
+  // the vertical scroll offset from 500 to 0, and get us into overscroll.
+  for (int i = 0; i < 6; ++i) {
+    mcc->AdvanceByMillis(frameLength);
+    PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+               ScreenPoint(0, -panPixelsPerFrame), mcc->Time());
+  }
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Pan further into overscroll at the same input velocity, enough
+  // for the frames while we are in overscroll to dominate the computation
+  // in the velocity tracker.
+  // Importantly, while the input velocity is still 100 pixels per frame,
+  // in the overscrolled state the page only visual moves by at most 8 pixels
+  // per frame.
+  int frames = StaticPrefs::apz_velocity_relevance_time_ms() / frameLength;
+  for (int i = 0; i < frames; ++i) {
+    mcc->AdvanceByMillis(frameLength);
+    PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+               ScreenPoint(0, -panPixelsPerFrame), mcc->Time());
+  }
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // End the pan, allowing an overscroll animation to start.
+  mcc->AdvanceByMillis(frameLength);
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, panPoint, ScreenPoint(0, 0),
+             mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+
+  // Check that the velocity reflects the actual movement (no more than 8
+  // pixels/frame ==> 0.8 pixels per millisecond), not the input velocity
+  // (100 pixels/frame ==> 10 pixels per millisecond). This ensures that
+  // the transition from the pan to the animation appears smooth.
+  // (Note: velocities are negative since they are upwards.)
+  EXPECT_LT(apzc->GetVelocityVector().y, 0);
+  EXPECT_GT(apzc->GetVelocityVector().y, -0.8);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTester, NoOverscrollForMousewheel) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  // Start scrolled down just a few pixels from the top.
+  metrics.SetVisualScrollOffset(CSSPoint(0, 3));
+  // Set line and page scroll amounts. Otherwise, even though Wheel() uses
+  // SCROLLDELTA_PIXEL, the wheel handling code will get confused by things
+  // like the "don't scroll more than one page" check.
+  metadata.SetPageScrollAmount(LayoutDeviceIntSize(50, 100));
+  metadata.SetLineScrollAmount(LayoutDeviceIntSize(5, 10));
+  apzc->SetScrollMetadata(metadata);
+
+  // Send a wheel with enough delta to scrollto y=0 *and* overscroll.
+  Wheel(apzc, ScreenIntPoint(10, 10), ScreenPoint(0, -10), mcc->Time());
+
+  // Check that we did not actually go into overscroll.
+  EXPECT_FALSE(apzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTester, ClickWhileOverscrolled) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  metrics.SetVisualScrollOffset(CSSPoint(0, 0));
+  apzc->SetFrameMetrics(metrics);
+
+  // Pan into overscroll at the top.
+  ScreenIntPoint panPoint(50, 50);
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, panPoint,
+             ScreenPoint(0, -1), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+             ScreenPoint(0, -100), mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->GetOverscrollAmount().y < 0);  // overscrolled at top
+
+  // End the pan. This should start an overscroll animation.
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, panPoint, ScreenPoint(0, 0),
+             mcc->Time());
+  EXPECT_TRUE(apzc->GetOverscrollAmount().y < 0);  // overscrolled at top
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+
+  // Send a mouse-down. This should interrupt the animation but not relieve
+  // overscroll yet.
+  ParentLayerPoint overscrollBefore = apzc->GetOverscrollAmount();
+  MouseDown(apzc, panPoint, mcc->Time());
+  EXPECT_FALSE(apzc->IsOverscrollAnimationRunning());
+  EXPECT_EQ(overscrollBefore, apzc->GetOverscrollAmount());
+
+  // Send a mouse-up. This should start an overscroll animation again.
+  MouseUp(apzc, panPoint, mcc->Time());
+  EXPECT_TRUE(apzc->IsOverscrollAnimationRunning());
+
+  SampleAnimationUntilRecoveredFromOverscroll(ParentLayerPoint(0, 0));
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTester, DynamicallyLoadingContent) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+  metrics.SetVisualScrollOffset(CSSPoint(0, 0));
+  apzc->SetFrameMetrics(metrics);
+
+  // Pan to the bottom of the page, and further, into overscroll.
+  ScreenIntPoint panPoint(50, 50);
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, panPoint,
+             ScreenPoint(0, 1), mcc->Time());
+  for (int i = 0; i < 12; ++i) {
+    mcc->AdvanceByMillis(10);
+    PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+               ScreenPoint(0, 100), mcc->Time());
+  }
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->GetOverscrollAmount().y > 0);  // overscrolled at bottom
+
+  // Grow the scrollable rect at the bottom, simulating the page loading content
+  // dynamically.
+  CSSRect scrollableRect = metrics.GetScrollableRect();
+  scrollableRect.height += 500;
+  metrics.SetScrollableRect(scrollableRect);
+  apzc->NotifyLayersUpdated(metadata, false, true);
+
+  // Check that the modified scrollable rect cleared the overscroll.
+  EXPECT_FALSE(apzc->IsOverscrolled());
+
+  // Pan back up to the top, and further, into overscroll.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, panPoint,
+             ScreenPoint(0, -1), mcc->Time());
+  for (int i = 0; i < 12; ++i) {
+    mcc->AdvanceByMillis(10);
+    PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+               ScreenPoint(0, -100), mcc->Time());
+  }
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  ParentLayerPoint overscrollAmount = apzc->GetOverscrollAmount();
+  EXPECT_TRUE(overscrollAmount.y < 0);  // overscrolled at top
+
+  // Grow the scrollable rect at the bottom again.
+  scrollableRect = metrics.GetScrollableRect();
+  scrollableRect.height += 500;
+  metrics.SetScrollableRect(scrollableRect);
+  apzc->NotifyLayersUpdated(metadata, false, true);
+
+  // Check that the modified scrollable rect did NOT clear overscroll at the
+  // top.
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_EQ(overscrollAmount,
+            apzc->GetOverscrollAmount());  // overscroll did not change at all
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTester, SmallAmountOfOverscroll) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+
+  // Do vertical overscroll first.
+  ScreenIntPoint panPoint(50, 50);
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, panPoint,
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, panPoint, ScreenPoint(0, 0),
+             mcc->Time());
+  mcc->AdvanceByMillis(10);
+
+  // Then do small horizontal overscroll which will be considered as "finished"
+  // by our overscroll animation physics model.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, panPoint,
+             ScreenPoint(-0.1, 0), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+             ScreenPoint(-0.2, 0), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, panPoint, ScreenPoint(0, 0),
+             mcc->Time());
+  mcc->AdvanceByMillis(10);
+
+  EXPECT_TRUE(apzc->IsOverscrolled());
+  EXPECT_TRUE(apzc->GetOverscrollAmount().y < 0);  // overscrolled at top
+  EXPECT_TRUE(apzc->GetOverscrollAmount().x < 0);  // and overscrolled at left
+
+  // Then do vertical scroll.
+  PanGesture(PanGestureInput::PANGESTURE_START, apzc, panPoint,
+             ScreenPoint(0, 10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, apzc, panPoint,
+             ScreenPoint(0, 100), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  PanGesture(PanGestureInput::PANGESTURE_END, apzc, panPoint, ScreenPoint(0, 0),
+             mcc->Time());
+
+  ParentLayerPoint scrollOffset =
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting);
+  EXPECT_GT(scrollOffset.y, 0);  // Make sure the vertical scroll offset is
+                                 // greater than zero.
+
+  // The small horizontal overscroll amount should be restored to zero.
+  ParentLayerPoint expectedScrollOffset(0, scrollOffset.y);
+  SampleAnimationUntilRecoveredFromOverscroll(expectedScrollOffset);
+}
+#endif
+
+#ifdef MOZ_WIDGET_ANDROID  // Only applies to WidgetOverscrollEffect
+TEST_F(APZCOverscrollTester, StuckInOverscroll_Bug1786452) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  ScrollMetadata metadata;
+  FrameMetrics& metrics = metadata.GetMetrics();
+  metrics.SetCompositionBounds(ParentLayerRect(0, 0, 100, 100));
+  metrics.SetScrollableRect(CSSRect(0, 0, 100, 1000));
+
+  // Over the course of the test, expect one or more calls to
+  // UpdateOverscrollOffset(), followed by a call to UpdateOverscrollVelocity().
+  // The latter ensures the widget has a chance to end its overscroll effect.
+  InSequence s;
+  EXPECT_CALL(*mcc, UpdateOverscrollOffset(_, _, _, _)).Times(AtLeast(1));
+  EXPECT_CALL(*mcc, UpdateOverscrollVelocity(_, _, _, _)).Times(1);
+
+  // Pan into overscroll, keeping the finger down
+  ScreenIntPoint startPoint(10, 500);
+  ScreenIntPoint endPoint(10, 10);
+  Pan(apzc, startPoint, endPoint, PanOptions::KeepFingerDown);
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Linger a while to cause the velocity to drop to very low or zero
+  mcc->AdvanceByMillis(100);
+  TouchMove(apzc, endPoint, mcc->Time());
+  EXPECT_LT(apzc->GetVelocityVector().Length(),
+            StaticPrefs::apz_fling_min_velocity_threshold());
+  EXPECT_TRUE(apzc->IsOverscrolled());
+
+  // Lift the finger
+  mcc->AdvanceByMillis(20);
+  TouchUp(apzc, endPoint, mcc->Time());
+  EXPECT_FALSE(apzc->IsOverscrolled());
+}
+#endif
+
+class APZCOverscrollTesterMock : public APZCTreeManagerTester {
+ public:
+  APZCOverscrollTesterMock() { CreateMockHitTester(); }
+
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+  TestAsyncPanZoomController* rootApzc;
+};
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTesterMock, OverscrollHandoff) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                         LayerIntRect(0, 0, 100, 50)};
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 200, 200));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            // same size as the visible region so that
+                            // the container is not scrollable in any directions
+                            // actually. This is simulating overflow: hidden
+                            // iframe document in Fission, though we don't set
+                            // a different layers id.
+                            CSSRect(0, 0, 100, 50));
+
+  SetScrollHandoff(layers[1], root);
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  rootApzc = ApzcOf(root);
+  rootApzc->GetFrameMetrics().SetIsRootContent(true);
+
+  // A pan gesture on the child scroller (which is not scrollable though).
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 20),
+             ScreenPoint(0, -2), mcc->Time());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTesterMock, VerticalOverscrollHandoffToScrollableRoot) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Create a layer tree having two vertical scrollable layers.
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                         LayerIntRect(0, 0, 100, 50)};
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 200));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            CSSRect(0, 0, 100, 200));
+
+  SetScrollHandoff(layers[1], root);
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  rootApzc = ApzcOf(root);
+  rootApzc->GetFrameMetrics().SetIsRootContent(true);
+
+  // A vertical pan gesture on the child scroller which will be handed off to
+  // the root APZC.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 20),
+             ScreenPoint(0, -2), mcc->Time());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  EXPECT_FALSE(ApzcOf(layers[1])->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTesterMock, NoOverscrollHandoffToNonScrollableRoot) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Create a layer tree having non-scrollable root and a vertical scrollable
+  // child.
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                         LayerIntRect(0, 0, 100, 50)};
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 100));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            CSSRect(0, 0, 100, 200));
+
+  SetScrollHandoff(layers[1], root);
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  rootApzc = ApzcOf(root);
+  rootApzc->GetFrameMetrics().SetIsRootContent(true);
+
+  // A vertical pan gesture on the child scroller which should not be handed
+  // off the root APZC.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 20),
+             ScreenPoint(0, -2), mcc->Time());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+  EXPECT_TRUE(ApzcOf(layers[1])->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCOverscrollTesterMock, NoOverscrollHandoffOrthogonalPanGesture) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Create a layer tree having horizontal scrollable root and a vertical
+  // scrollable child.
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                         LayerIntRect(0, 0, 100, 50)};
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 200, 100));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            CSSRect(0, 0, 100, 200));
+
+  SetScrollHandoff(layers[1], root);
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  rootApzc = ApzcOf(root);
+  rootApzc->GetFrameMetrics().SetIsRootContent(true);
+
+  // A vertical pan gesture on the child scroller which should not be handed
+  // off the root APZC because the root APZC is not scrollable vertically.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 20),
+             ScreenPoint(0, -2), mcc->Time());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+  EXPECT_TRUE(ApzcOf(layers[1])->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTesterMock,
+       RetriggerCancelledOverscrollAnimationByNewPanGesture) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Create a layer tree having vertical scrollable root and a horizontal
+  // scrollable child.
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                         LayerIntRect(0, 0, 100, 50)};
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 200));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            CSSRect(0, 0, 200, 50));
+
+  SetScrollHandoff(layers[1], root);
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  rootApzc = ApzcOf(root);
+  rootApzc->GetFrameMetrics().SetIsRootContent(true);
+
+  ScreenIntPoint panPoint(50, 20);
+  // A vertical pan gesture on the child scroller which should be handed off the
+  // root APZC.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, panPoint,
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, panPoint,
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, panPoint,
+             ScreenPoint(0, 0), mcc->Time());
+
+  // The root APZC should be overscrolled and the child APZC should not be.
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  EXPECT_FALSE(ApzcOf(layers[1])->IsOverscrolled());
+
+  mcc->AdvanceByMillis(10);
+
+  // Make sure the root APZC is still overscrolled.
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+
+  // Start a new horizontal pan gesture on the child scroller which should be
+  // handled by the child APZC now.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  APZEventResult result = PanGesture(PanGestureInput::PANGESTURE_START, manager,
+                                     panPoint, ScreenPoint(-2, 0), mcc->Time());
+  // The above horizontal pan start event was flagged as "this event may trigger
+  // swipe" and either the root scrollable frame or the horizontal child
+  // scrollable frame is not scrollable in the pan start direction, thus the pan
+  // start event run into the short circuit path for swipe-to-navigation in
+  // InputQueue::ReceivePanGestureInput, which means it's waiting for the
+  // content response, so we need to respond explicitly here.
+  manager->ContentReceivedInputBlock(result.mInputBlockId, false);
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, panPoint,
+             ScreenPoint(-10, 0), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, panPoint,
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Now both APZCs should be overscrolled.
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  EXPECT_TRUE(ApzcOf(layers[1])->IsOverscrolled());
+
+  // Sample all animations until all of them have been finished.
+  while (SampleAnimationsOnce())
+    ;
+
+  // After the animations finished, all overscrolled states should have been
+  // restored.
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+  EXPECT_FALSE(ApzcOf(layers[1])->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTesterMock, RetriggeredOverscrollAnimationVelocity) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  // Setup two nested vertical scrollable frames.
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                         LayerIntRect(0, 0, 100, 50)};
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 200));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            CSSRect(0, 0, 100, 200));
+
+  SetScrollHandoff(layers[1], root);
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  rootApzc = ApzcOf(root);
+  rootApzc->GetFrameMetrics().SetIsRootContent(true);
+
+  ScreenIntPoint panPoint(50, 20);
+  // A vertical upward pan gesture on the child scroller which should be handed
+  // off the root APZC.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, panPoint,
+             ScreenPoint(0, -2), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, panPoint,
+             ScreenPoint(0, -10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, panPoint,
+             ScreenPoint(0, 0), mcc->Time());
+
+  // The root APZC should be overscrolled and the child APZC should not be.
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  EXPECT_FALSE(ApzcOf(layers[1])->IsOverscrolled());
+
+  mcc->AdvanceByMillis(10);
+
+  // Make sure the root APZC is still overscrolled and there's an overscroll
+  // animation.
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  EXPECT_TRUE(rootApzc->IsOverscrollAnimationRunning());
+
+  // And make sure the overscroll animation's velocity is a certain amount in
+  // the upward direction.
+  EXPECT_LT(rootApzc->GetVelocityVector().y, 0);
+
+  // Start a new downward pan gesture on the child scroller which
+  // should be handled by the child APZC now.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, panPoint,
+             ScreenPoint(0, 2), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  // The new pan-start gesture stops the overscroll animation at this moment.
+  EXPECT_TRUE(!rootApzc->IsOverscrollAnimationRunning());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, panPoint,
+             ScreenPoint(0, 10), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  // There's no overscroll animation yet even if the root APZC is still
+  // overscrolled.
+  EXPECT_TRUE(!rootApzc->IsOverscrollAnimationRunning());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, panPoint,
+             ScreenPoint(0, 10), mcc->Time());
+
+  // Now an overscroll animation should have been triggered by the pan-end
+  // gesture.
+  EXPECT_TRUE(rootApzc->IsOverscrollAnimationRunning());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  // And the newly created overscroll animation's positions should never exceed
+  // 0.
+  while (SampleAnimationsOnce()) {
+    EXPECT_LE(rootApzc->GetOverscrollAmount().y, 0);
+  }
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Only applies to GenericOverscrollEffect
+TEST_F(APZCOverscrollTesterMock, OverscrollIntoPreventDefault) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  const char* treeShape = "x";
+  LayerIntRegion layerVisibleRegions[] = {LayerIntRect(0, 0, 100, 100)};
+  CreateScrollData(treeShape, layerVisibleRegions);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 200));
+
+  registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  rootApzc = ApzcOf(root);
+
+  // Start a pan gesture a few pixels below the 20px DTC region.
+  ScreenIntPoint cursorLocation(10, 25);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  APZEventResult result =
+      PanGesture(PanGestureInput::PANGESTURE_START, manager, cursorLocation,
+                 ScreenPoint(0, -2), mcc->Time());
+
+  // At this point, we should be overscrolled.
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+
+  // Pan further, until the DTC region is under the cursor.
+  // Note that, due to ApplyResistance(), we need a large input delta to cause a
+  // visual transform enough to bridge the 5px to the DTC region.
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, cursorLocation,
+             ScreenPoint(0, -100), mcc->Time());
+
+  // At this point, we are still overscrolled. Record the overscroll amount.
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  float overscrollY = rootApzc->GetOverscrollAmount().y;
+
+  // Send a content response with preventDefault = true.
+  manager->SetAllowedTouchBehavior(result.mInputBlockId,
+                                   {AllowedTouchBehavior::VERTICAL_PAN});
+  manager->SetTargetAPZC(result.mInputBlockId, {result.mTargetGuid});
+  manager->ContentReceivedInputBlock(result.mInputBlockId,
+                                     /*aPreventDefault=*/true);
+
+  // The content response has the effect of interrupting the input block
+  // but no processing happens yet (as there are no events in the block).
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  EXPECT_EQ(overscrollY, rootApzc->GetOverscrollAmount().y);
+
+  // Send one more pan event. This starts a new, *unconfirmed* input block
+  // (via the "transmogrify" codepath).
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  result = PanGesture(PanGestureInput::PANGESTURE_PAN, manager, cursorLocation,
+                      ScreenPoint(0, -10), mcc->Time());
+
+  // No overscroll occurs (the event is waiting in the queue for confirmation).
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+  EXPECT_EQ(overscrollY, rootApzc->GetOverscrollAmount().y);
+
+  // preventDefault the new event as well
+  manager->SetAllowedTouchBehavior(result.mInputBlockId,
+                                   {AllowedTouchBehavior::VERTICAL_PAN});
+  manager->SetTargetAPZC(result.mInputBlockId, {result.mTargetGuid});
+  manager->ContentReceivedInputBlock(result.mInputBlockId,
+                                     /*aPreventDefault=*/true);
+
+  // This should trigger clearing the overscrolling and resetting the state.
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+  rootApzc->AssertStateIsReset();
+
+  // If there are momentum events after this point, they should not cause
+  // further scrolling or overscorll.
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  result = PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, manager,
+                      cursorLocation, ScreenPoint(0, -100), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  result = PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, manager,
+                      cursorLocation, ScreenPoint(0, -100), mcc->Time());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+  EXPECT_EQ(rootApzc->GetFrameMetrics().GetVisualScrollOffset(),
+            CSSPoint(0, 0));
+}
+#endif
diff --git a/gfx/layers/apz/test/gtest/TestPanning.cpp b/gfx/layers/apz/test/gtest/TestPanning.cpp
new file mode 100644
index 0000000000..b0024db99b
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestPanning.cpp
@@ -0,0 +1,219 @@
+/* -*- 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 "APZCBasicTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+#include "gtest/gtest.h"
+
+class APZCPanningTester : public APZCBasicTester {
+ protected:
+  void DoPanTest(bool aShouldTriggerScroll, bool aShouldBeConsumed,
+                 uint32_t aBehavior) {
+    if (aShouldTriggerScroll) {
+      // Three repaint request for each pan.
+      EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(6);
+    } else {
+      EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(0);
+    }
+
+    int touchStart = 50;
+    int touchEnd = 10;
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+
+    nsTArray<uint32_t> allowedTouchBehaviors;
+    allowedTouchBehaviors.AppendElement(aBehavior);
+
+    // Pan down
+    PanAndCheckStatus(apzc, touchStart, touchEnd, aShouldBeConsumed,
+                      &allowedTouchBehaviors);
+    apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+
+    if (aShouldTriggerScroll) {
+      EXPECT_EQ(ParentLayerPoint(0, -(touchEnd - touchStart)), pointOut);
+      EXPECT_NE(AsyncTransform(), viewTransformOut);
+    } else {
+      EXPECT_EQ(ParentLayerPoint(), pointOut);
+      EXPECT_EQ(AsyncTransform(), viewTransformOut);
+    }
+
+    // Clear the fling from the previous pan, or stopping it will
+    // consume the next touchstart
+    apzc->CancelAnimation();
+
+    // Pan back
+    PanAndCheckStatus(apzc, touchEnd, touchStart, aShouldBeConsumed,
+                      &allowedTouchBehaviors);
+    apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+
+    EXPECT_EQ(ParentLayerPoint(), pointOut);
+    EXPECT_EQ(AsyncTransform(), viewTransformOut);
+  }
+
+  void DoPanWithPreventDefaultTest() {
+    MakeApzcWaitForMainThread();
+
+    int touchStart = 50;
+    int touchEnd = 10;
+    ParentLayerPoint pointOut;
+    AsyncTransform viewTransformOut;
+    uint64_t blockId = 0;
+
+    // Pan down
+    nsTArray<uint32_t> allowedTouchBehaviors;
+    allowedTouchBehaviors.AppendElement(
+        mozilla::layers::AllowedTouchBehavior::VERTICAL_PAN);
+    PanAndCheckStatus(apzc, touchStart, touchEnd, true, &allowedTouchBehaviors,
+                      &blockId);
+
+    // Send the signal that content has handled and preventDefaulted the touch
+    // events. This flushes the event queue.
+    apzc->ContentReceivedInputBlock(blockId, true);
+
+    apzc->SampleContentTransformForFrame(&viewTransformOut, pointOut);
+    EXPECT_EQ(ParentLayerPoint(), pointOut);
+    EXPECT_EQ(AsyncTransform(), viewTransformOut);
+
+    apzc->AssertStateIsReset();
+  }
+};
+
+// In the each of the following 4 pan tests we are performing two pan gestures:
+// vertical pan from top to bottom and back - from bottom to top. According to
+// the pointer-events/touch-action spec AUTO and PAN_Y touch-action values allow
+// vertical scrolling while NONE and PAN_X forbid it. The first parameter of
+// DoPanTest method specifies this behavior. However, the events will be marked
+// as consumed even if the behavior in PAN_X, because the user could move their
+// finger horizontally too - APZ has no way of knowing beforehand and so must
+// consume the events.
+TEST_F(APZCPanningTester, PanWithTouchActionAuto) {
+  // Velocity bias can cause extra repaint requests.
+  SCOPED_GFX_PREF_FLOAT("apz.velocity_bias", 0.0);
+  DoPanTest(true, true,
+            mozilla::layers::AllowedTouchBehavior::HORIZONTAL_PAN |
+                mozilla::layers::AllowedTouchBehavior::VERTICAL_PAN);
+}
+
+TEST_F(APZCPanningTester, PanWithTouchActionNone) {
+  // Velocity bias can cause extra repaint requests.
+  SCOPED_GFX_PREF_FLOAT("apz.velocity_bias", 0.0);
+  DoPanTest(false, false, 0);
+}
+
+TEST_F(APZCPanningTester, PanWithTouchActionPanX) {
+  // Velocity bias can cause extra repaint requests.
+  SCOPED_GFX_PREF_FLOAT("apz.velocity_bias", 0.0);
+  DoPanTest(false, false,
+            mozilla::layers::AllowedTouchBehavior::HORIZONTAL_PAN);
+}
+
+TEST_F(APZCPanningTester, PanWithTouchActionPanY) {
+  // Velocity bias can cause extra repaint requests.
+  SCOPED_GFX_PREF_FLOAT("apz.velocity_bias", 0.0);
+  DoPanTest(true, true, mozilla::layers::AllowedTouchBehavior::VERTICAL_PAN);
+}
+
+TEST_F(APZCPanningTester, PanWithPreventDefault) {
+  DoPanWithPreventDefaultTest();
+}
+
+TEST_F(APZCPanningTester, PanWithHistoricalTouchData) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0);
+
+  // Simulate the same pan gesture, in three different ways.
+  // We start at y=50, with a 50ms resting period at the start of the pan.
+  // Then we accelerate the finger upwards towards y=10, reaching a 10px/10ms
+  // velocity towards the end of the panning motion.
+  //
+  // The first simulation fires touch move events with 10ms gaps.
+  // The second simulation skips two of the touch move events, simulating
+  // "jank". The third simulation also skips those two events, but reports the
+  // missed positions in the following event's historical coordinates.
+  //
+  // Consequently, the first and third simulation should estimate the same
+  // velocities, whereas the second simulation should estimate a different
+  // velocity because it is missing data.
+
+  // First simulation: full data
+
+  APZEventResult result = TouchDown(apzc, ScreenIntPoint(0, 50), mcc->Time());
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(apzc, result.mInputBlockId);
+  }
+
+  mcc->AdvanceByMillis(50);
+  result = TouchMove(apzc, ScreenIntPoint(0, 45), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  result = TouchMove(apzc, ScreenIntPoint(0, 40), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  result = TouchMove(apzc, ScreenIntPoint(0, 30), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  result = TouchMove(apzc, ScreenIntPoint(0, 20), mcc->Time());
+  result = TouchUp(apzc, ScreenIntPoint(0, 20), mcc->Time());
+  auto velocityFromFullDataAsSeparateEvents = apzc->GetVelocityVector();
+  apzc->CancelAnimation();
+
+  mcc->AdvanceByMillis(100);
+
+  // Second simulation: partial data
+
+  result = TouchDown(apzc, ScreenIntPoint(0, 50), mcc->Time());
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(apzc, result.mInputBlockId);
+  }
+
+  mcc->AdvanceByMillis(50);
+  result = TouchMove(apzc, ScreenIntPoint(0, 45), mcc->Time());
+  mcc->AdvanceByMillis(30);
+  result = TouchMove(apzc, ScreenIntPoint(0, 20), mcc->Time());
+  result = TouchUp(apzc, ScreenIntPoint(0, 20), mcc->Time());
+  auto velocityFromPartialData = apzc->GetVelocityVector();
+  apzc->CancelAnimation();
+
+  mcc->AdvanceByMillis(100);
+
+  // Third simulation: full data via historical data
+
+  result = TouchDown(apzc, ScreenIntPoint(0, 50), mcc->Time());
+  if (result.GetStatus() != nsEventStatus_eConsumeNoDefault) {
+    SetDefaultAllowedTouchBehavior(apzc, result.mInputBlockId);
+  }
+
+  mcc->AdvanceByMillis(50);
+  result = TouchMove(apzc, ScreenIntPoint(0, 45), mcc->Time());
+  mcc->AdvanceByMillis(30);
+
+  MultiTouchInput mti =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, mcc->Time());
+  auto singleTouchData = CreateSingleTouchData(0, ScreenIntPoint(0, 20));
+  singleTouchData.mHistoricalData.AppendElement(
+      SingleTouchData::HistoricalTouchData{
+          mcc->Time() - TimeDuration::FromMilliseconds(20),
+          ScreenIntPoint(0, 40),
+          {},
+          {},
+          0.0f,
+          0.0f});
+  singleTouchData.mHistoricalData.AppendElement(
+      SingleTouchData::HistoricalTouchData{
+          mcc->Time() - TimeDuration::FromMilliseconds(10),
+          ScreenIntPoint(0, 30),
+          {},
+          {},
+          0.0f,
+          0.0f});
+  mti.mTouches.AppendElement(singleTouchData);
+  result = apzc->ReceiveInputEvent(mti);
+
+  result = TouchUp(apzc, ScreenIntPoint(0, 20), mcc->Time());
+  auto velocityFromFullDataViaHistory = apzc->GetVelocityVector();
+  apzc->CancelAnimation();
+
+  EXPECT_EQ(velocityFromFullDataAsSeparateEvents,
+            velocityFromFullDataViaHistory);
+  EXPECT_NE(velocityFromPartialData, velocityFromFullDataViaHistory);
+}
diff --git a/gfx/layers/apz/test/gtest/TestPinching.cpp b/gfx/layers/apz/test/gtest/TestPinching.cpp
new file mode 100644
index 0000000000..f6d1280bf3
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestPinching.cpp
@@ -0,0 +1,675 @@
+/* -*- 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 "APZCBasicTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+#include "mozilla/StaticPrefs_apz.h"
+
+class APZCPinchTester : public APZCBasicTester {
+ private:
+  // This (multiplied by apz.touch_start_tolerance) needs to be the hypotenuse
+  // in a Pythagorean triple, along with overcomeTouchToleranceX and
+  // overcomeTouchToleranceY from APZCTesterBase::Pan().
+  // This is because APZCTesterBase::Pan(), when run without the
+  // PanOptions::ExactCoordinates option, will need to first overcome the
+  // touch start tolerance by performing a move of exactly
+  // (apz.touch_start_tolerance * DPI) length.
+  // When moving on both axes at once, we need to use integers for both legs
+  // (overcomeTouchToleranceX and overcomeTouchToleranceY) while making sure
+  // that the hypotenuse is also a round integer number (hence Pythagorean
+  // triples). (The hypotenuse is the length of the movement in this case.)
+  static const int mDPI = 100;
+
+ public:
+  explicit APZCPinchTester(
+      AsyncPanZoomController::GestureBehavior aGestureBehavior =
+          AsyncPanZoomController::DEFAULT_GESTURES)
+      : APZCBasicTester(aGestureBehavior) {}
+
+  void SetUp() override {
+    APZCBasicTester::SetUp();
+    tm->SetDPI(mDPI);
+  }
+
+ protected:
+  FrameMetrics GetPinchableFrameMetrics() {
+    FrameMetrics fm;
+    fm.SetCompositionBounds(ParentLayerRect(0, 0, 100, 200));
+    fm.SetScrollableRect(CSSRect(0, 0, 980, 1000));
+    fm.SetVisualScrollOffset(CSSPoint(300, 300));
+    fm.SetLayoutViewport(CSSRect(300, 300, 100, 200));
+    fm.SetZoom(CSSToParentLayerScale(2.0));
+    // APZC only allows zooming on the root scrollable frame.
+    fm.SetIsRootContent(true);
+    // the visible area of the document in CSS pixels is x=300 y=300 w=50 h=100
+    return fm;
+  }
+
+  void DoPinchTest(bool aShouldTriggerPinch,
+                   nsTArray<uint32_t>* aAllowedTouchBehaviors = nullptr) {
+    apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+    MakeApzcZoomable();
+
+    if (aShouldTriggerPinch) {
+      // One repaint request for each gesture.
+      EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(2);
+    } else {
+      EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(0);
+    }
+
+    int touchInputId = 0;
+    if (mGestureBehavior == AsyncPanZoomController::USE_GESTURE_DETECTOR) {
+      PinchWithTouchInputAndCheckStatus(apzc, ScreenIntPoint(250, 300), 1.25,
+                                        touchInputId, aShouldTriggerPinch,
+                                        aAllowedTouchBehaviors);
+    } else {
+      PinchWithPinchInputAndCheckStatus(apzc, ScreenIntPoint(250, 300), 1.25,
+                                        aShouldTriggerPinch);
+    }
+
+    apzc->AssertStateIsReset();
+
+    FrameMetrics fm = apzc->GetFrameMetrics();
+
+    if (aShouldTriggerPinch) {
+      // the visible area of the document in CSS pixels is now x=325 y=330 w=40
+      // h=80
+      EXPECT_EQ(2.5f, fm.GetZoom().scale);
+      EXPECT_EQ(325, fm.GetVisualScrollOffset().x);
+      EXPECT_EQ(330, fm.GetVisualScrollOffset().y);
+    } else {
+      // The frame metrics should stay the same since touch-action:none makes
+      // apzc ignore pinch gestures.
+      EXPECT_EQ(2.0f, fm.GetZoom().scale);
+      EXPECT_EQ(300, fm.GetVisualScrollOffset().x);
+      EXPECT_EQ(300, fm.GetVisualScrollOffset().y);
+    }
+
+    // part 2 of the test, move to the top-right corner of the page and pinch
+    // and make sure we stay in the correct spot
+    fm.SetZoom(CSSToParentLayerScale(2.0));
+    fm.SetVisualScrollOffset(CSSPoint(930, 5));
+    apzc->SetFrameMetrics(fm);
+    // the visible area of the document in CSS pixels is x=930 y=5 w=50 h=100
+
+    if (mGestureBehavior == AsyncPanZoomController::USE_GESTURE_DETECTOR) {
+      PinchWithTouchInputAndCheckStatus(apzc, ScreenIntPoint(250, 300), 0.5,
+                                        touchInputId, aShouldTriggerPinch,
+                                        aAllowedTouchBehaviors);
+    } else {
+      PinchWithPinchInputAndCheckStatus(apzc, ScreenIntPoint(250, 300), 0.5,
+                                        aShouldTriggerPinch);
+    }
+
+    apzc->AssertStateIsReset();
+
+    fm = apzc->GetFrameMetrics();
+
+    if (aShouldTriggerPinch) {
+      // the visible area of the document in CSS pixels is now x=805 y=0 w=100
+      // h=200
+      EXPECT_EQ(1.0f, fm.GetZoom().scale);
+      EXPECT_EQ(805, fm.GetVisualScrollOffset().x);
+      EXPECT_EQ(0, fm.GetVisualScrollOffset().y);
+    } else {
+      EXPECT_EQ(2.0f, fm.GetZoom().scale);
+      EXPECT_EQ(930, fm.GetVisualScrollOffset().x);
+      EXPECT_EQ(5, fm.GetVisualScrollOffset().y);
+    }
+  }
+};
+
+class APZCPinchGestureDetectorTester : public APZCPinchTester {
+ public:
+  APZCPinchGestureDetectorTester()
+      : APZCPinchTester(AsyncPanZoomController::USE_GESTURE_DETECTOR) {}
+
+  void DoPinchWithPreventDefaultTest() {
+    FrameMetrics originalMetrics = GetPinchableFrameMetrics();
+    apzc->SetFrameMetrics(originalMetrics);
+
+    MakeApzcWaitForMainThread();
+    MakeApzcZoomable();
+
+    int touchInputId = 0;
+    uint64_t blockId = 0;
+    PinchWithTouchInput(apzc, ScreenIntPoint(250, 300), 1.25, touchInputId,
+                        nullptr, nullptr, &blockId);
+
+    // Send the prevent-default notification for the touch block
+    apzc->ContentReceivedInputBlock(blockId, true);
+
+    // verify the metrics didn't change (i.e. the pinch was ignored)
+    FrameMetrics fm = apzc->GetFrameMetrics();
+    EXPECT_EQ(originalMetrics.GetZoom(), fm.GetZoom());
+    EXPECT_EQ(originalMetrics.GetVisualScrollOffset().x,
+              fm.GetVisualScrollOffset().x);
+    EXPECT_EQ(originalMetrics.GetVisualScrollOffset().y,
+              fm.GetVisualScrollOffset().y);
+
+    apzc->AssertStateIsReset();
+  }
+};
+
+class APZCPinchLockingTester : public APZCPinchTester {
+ private:
+  ScreenIntPoint mFocus;
+  float mSpan;
+  int mPinchLockBufferMaxAge;
+
+ public:
+  APZCPinchLockingTester()
+      : APZCPinchTester(AsyncPanZoomController::USE_GESTURE_DETECTOR),
+        mFocus(ScreenIntPoint(200, 300)),
+        mSpan(10.0) {}
+
+  virtual void SetUp() {
+    mPinchLockBufferMaxAge =
+        StaticPrefs::apz_pinch_lock_buffer_max_age_AtStartup();
+
+    APZCPinchTester::SetUp();
+    apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+    MakeApzcZoomable();
+
+    auto event = CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_START,
+                                         mFocus, mSpan, mSpan, mcc->Time());
+    apzc->ReceiveInputEvent(event);
+    mcc->AdvanceBy(TimeDuration::FromMilliseconds(mPinchLockBufferMaxAge + 1));
+  }
+
+  void twoFingerPan() {
+    ScreenCoord panDistance =
+        StaticPrefs::apz_pinch_lock_scroll_lock_threshold() * 1.2 *
+        tm->GetDPI();
+
+    mFocus = ScreenIntPoint((int)(mFocus.x.value + panDistance),
+                            (int)(mFocus.y.value));
+
+    auto event = CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_SCALE,
+                                         mFocus, mSpan, mSpan, mcc->Time());
+    apzc->ReceiveInputEvent(event);
+    mcc->AdvanceBy(TimeDuration::FromMilliseconds(mPinchLockBufferMaxAge + 1));
+  }
+
+  void twoFingerZoom() {
+    float pinchDistance =
+        StaticPrefs::apz_pinch_lock_span_breakout_threshold() * 1.2 *
+        tm->GetDPI();
+
+    float newSpan = mSpan + pinchDistance;
+
+    auto event = CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_SCALE,
+                                         mFocus, newSpan, mSpan, mcc->Time());
+    apzc->ReceiveInputEvent(event);
+    mcc->AdvanceBy(TimeDuration::FromMilliseconds(mPinchLockBufferMaxAge + 1));
+    mSpan = newSpan;
+  }
+
+  bool isPinchLockActive() {
+    FrameMetrics originalMetrics = apzc->GetFrameMetrics();
+
+    // Send a small scale input to the APZC
+    float pinchDistance =
+        StaticPrefs::apz_pinch_lock_span_breakout_threshold() * 0.8 *
+        tm->GetDPI();
+    auto event =
+        CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_SCALE, mFocus,
+                                mSpan + pinchDistance, mSpan, mcc->Time());
+    apzc->ReceiveInputEvent(event);
+
+    FrameMetrics result = apzc->GetFrameMetrics();
+    bool lockActive = originalMetrics.GetZoom() == result.GetZoom() &&
+                      originalMetrics.GetVisualScrollOffset().x ==
+                          result.GetVisualScrollOffset().x &&
+                      originalMetrics.GetVisualScrollOffset().y ==
+                          result.GetVisualScrollOffset().y;
+
+    // Avoid side effects, reset to original frame metrics
+    apzc->SetFrameMetrics(originalMetrics);
+    return lockActive;
+  }
+};
+
+TEST_F(APZCPinchGestureDetectorTester,
+       Pinch_UseGestureDetector_TouchActionNone) {
+  nsTArray<uint32_t> behaviors = {mozilla::layers::AllowedTouchBehavior::NONE,
+                                  mozilla::layers::AllowedTouchBehavior::NONE};
+  DoPinchTest(false, &behaviors);
+}
+
+TEST_F(APZCPinchGestureDetectorTester,
+       Pinch_UseGestureDetector_TouchActionZoom) {
+  nsTArray<uint32_t> behaviors;
+  behaviors.AppendElement(mozilla::layers::AllowedTouchBehavior::PINCH_ZOOM);
+  behaviors.AppendElement(mozilla::layers::AllowedTouchBehavior::PINCH_ZOOM);
+  DoPinchTest(true, &behaviors);
+}
+
+TEST_F(APZCPinchGestureDetectorTester,
+       Pinch_UseGestureDetector_TouchActionNotAllowZoom) {
+  nsTArray<uint32_t> behaviors;
+  behaviors.AppendElement(mozilla::layers::AllowedTouchBehavior::NONE);
+  behaviors.AppendElement(mozilla::layers::AllowedTouchBehavior::PINCH_ZOOM);
+  DoPinchTest(false, &behaviors);
+}
+
+TEST_F(APZCPinchGestureDetectorTester,
+       Pinch_UseGestureDetector_TouchActionNone_NoAPZZoom) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_zooming", false);
+
+  // Since we are preventing the pinch action via touch-action we should not be
+  // sending the pinch gesture notifications that would normally be sent when
+  // apz_allow_zooming is false.
+  EXPECT_CALL(*mcc, NotifyPinchGesture(_, _, _, _, _)).Times(0);
+  nsTArray<uint32_t> behaviors = {mozilla::layers::AllowedTouchBehavior::NONE,
+                                  mozilla::layers::AllowedTouchBehavior::NONE};
+  DoPinchTest(false, &behaviors);
+}
+
+TEST_F(APZCPinchGestureDetectorTester, Pinch_PreventDefault) {
+  DoPinchWithPreventDefaultTest();
+}
+
+TEST_F(APZCPinchGestureDetectorTester, Pinch_PreventDefault_NoAPZZoom) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_zooming", false);
+
+  // Since we are preventing the pinch action we should not be sending the pinch
+  // gesture notifications that would normally be sent when apz_allow_zooming is
+  // false.
+  EXPECT_CALL(*mcc, NotifyPinchGesture(_, _, _, _, _)).Times(0);
+
+  DoPinchWithPreventDefaultTest();
+}
+
+TEST_F(APZCPinchGestureDetectorTester, Panning_TwoFingerFling_ZoomDisabled) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcUnzoomable();
+
+  // Perform a two finger pan
+  int touchInputId = 0;
+  uint64_t blockId = 0;
+  PinchWithTouchInput(apzc, ScreenIntPoint(100, 200), ScreenIntPoint(100, 100),
+                      1, touchInputId, nullptr, nullptr, &blockId);
+
+  // Expect to be in a flinging state
+  apzc->AssertStateIsFling();
+}
+
+TEST_F(APZCPinchGestureDetectorTester, Pinch_DoesntFling_ZoomDisabled) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcUnzoomable();
+
+  // Perform a pinch
+  int touchInputId = 0;
+  uint64_t blockId = 0;
+
+  PinchWithTouchInput(apzc, ScreenIntPoint(100, 200), ScreenIntPoint(100, 100),
+                      2, touchInputId, nullptr, nullptr, &blockId,
+                      PinchOptions::LiftFinger2, true);
+
+  // Lift second finger after a pause
+  mcc->AdvanceBy(TimeDuration::FromMilliseconds(50));
+  TouchUp(apzc, ScreenIntPoint(100, 100), mcc->Time());
+
+  // Pinch should not trigger a fling
+  EXPECT_EQ(apzc->GetVelocityVector().y, 0);
+}
+
+TEST_F(APZCPinchGestureDetectorTester, Panning_TwoFingerFling_ZoomEnabled) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcZoomable();
+
+  // Perform a two finger pan
+  int touchInputId = 0;
+  uint64_t blockId = 0;
+  PinchWithTouchInput(apzc, ScreenIntPoint(100, 200), ScreenIntPoint(100, 100),
+                      1, touchInputId, nullptr, nullptr, &blockId);
+
+  // Expect to NOT be in flinging state
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCPinchGestureDetectorTester,
+       Panning_TwoThenOneFingerFling_ZoomEnabled) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcZoomable();
+
+  // Perform a two finger pan lifting only the first finger
+  int touchInputId = 0;
+  uint64_t blockId = 0;
+  PinchWithTouchInput(apzc, ScreenIntPoint(100, 200), ScreenIntPoint(100, 100),
+                      1, touchInputId, nullptr, nullptr, &blockId,
+                      PinchOptions::LiftFinger2);
+
+  // Lift second finger after a pause
+  mcc->AdvanceBy(TimeDuration::FromMilliseconds(50));
+  TouchUp(apzc, ScreenIntPoint(100, 100), mcc->Time());
+
+  // This gesture should activate the pinch lock, and result
+  // in a fling even if the page is zoomable.
+  apzc->AssertStateIsFling();
+}
+
+TEST_F(APZCPinchGestureDetectorTester,
+       Panning_TwoThenOneFingerFling_ZoomDisabled) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcUnzoomable();
+
+  // Perform a two finger pan lifting only the first finger
+  int touchInputId = 0;
+  uint64_t blockId = 0;
+  PinchWithTouchInput(apzc, ScreenIntPoint(100, 200), ScreenIntPoint(100, 100),
+                      1, touchInputId, nullptr, nullptr, &blockId,
+                      PinchOptions::LiftFinger2);
+
+  // Lift second finger after a pause
+  mcc->AdvanceBy(TimeDuration::FromMilliseconds(50));
+  TouchUp(apzc, ScreenIntPoint(100, 100), mcc->Time());
+
+  // This gesture should activate the pinch lock and result in a fling
+  apzc->AssertStateIsFling();
+}
+
+TEST_F(APZCPinchTester, Panning_TwoFinger_ZoomDisabled) {
+  // set up APZ
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcUnzoomable();
+
+  nsEventStatus statuses[3];  // scalebegin, scale, scaleend
+  PinchWithPinchInput(apzc, ScreenIntPoint(250, 350), ScreenIntPoint(200, 300),
+                      10, &statuses);
+
+  FrameMetrics fm = apzc->GetFrameMetrics();
+
+  // It starts from (300, 300), then moves the focus point from (250, 350) to
+  // (200, 300) pans by (50, 50) screen pixels, but there is a 2x zoom, which
+  // causes the scroll offset to change by half of that (25, 25) pixels.
+  EXPECT_EQ(325, fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(325, fm.GetVisualScrollOffset().y);
+  EXPECT_EQ(2.0, fm.GetZoom().scale);
+}
+
+TEST_F(APZCPinchTester, Panning_Beyond_LayoutViewport) {
+  SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 0);
+
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcZoomable();
+
+  // Case 1 - visual viewport is still inside layout viewport.
+  Pan(apzc, 350, 300, PanOptions::NoFling);
+  FrameMetrics fm = apzc->GetFrameMetrics();
+  // It starts from (300, 300) pans by (0, 50) screen pixels, but there is a
+  // 2x zoom, which causes the scroll offset to change by half of that (0, 25).
+  // But the visual viewport is still inside the layout viewport.
+  EXPECT_EQ(300, fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(325, fm.GetVisualScrollOffset().y);
+  EXPECT_EQ(300, fm.GetLayoutViewport().X());
+  EXPECT_EQ(300, fm.GetLayoutViewport().Y());
+
+  // Case 2 - visual viewport crosses the bottom boundary of the layout
+  // viewport.
+  Pan(apzc, 525, 325, PanOptions::NoFling);
+  fm = apzc->GetFrameMetrics();
+  // It starts from (300, 325) pans by (0, 200) screen pixels, but there is a
+  // 2x zoom, which causes the scroll offset to change by half of that
+  // (0, 100). The visual viewport crossed the bottom boundary of the layout
+  // viewport by 25px.
+  EXPECT_EQ(300, fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(425, fm.GetVisualScrollOffset().y);
+  EXPECT_EQ(300, fm.GetLayoutViewport().X());
+  EXPECT_EQ(325, fm.GetLayoutViewport().Y());
+
+  // Case 3 - visual viewport crosses the top boundary of the layout viewport.
+  Pan(apzc, 425, 775, PanOptions::NoFling);
+  fm = apzc->GetFrameMetrics();
+  // It starts from (300, 425) pans by (0, -350) screen pixels, but there is a
+  // 2x zoom, which causes the scroll offset to change by half of that
+  // (0, -175). The visual viewport crossed the top of the layout viewport by
+  // 75px.
+  EXPECT_EQ(300, fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(250, fm.GetVisualScrollOffset().y);
+  EXPECT_EQ(300, fm.GetLayoutViewport().X());
+  EXPECT_EQ(250, fm.GetLayoutViewport().Y());
+
+  // Case 4 - visual viewport crosses the left boundary of the layout viewport.
+  Pan(apzc, ScreenIntPoint(150, 10), ScreenIntPoint(350, 10),
+      PanOptions::NoFling);
+  fm = apzc->GetFrameMetrics();
+  // It starts from (300, 250) pans by (-200, 0) screen pixels, but there is a
+  // 2x zoom, which causes the scroll offset to change by half of that
+  // (-100, 0). The visual viewport crossed the left boundary of the layout
+  // viewport by 100px.
+  EXPECT_EQ(200, fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(250, fm.GetVisualScrollOffset().y);
+  EXPECT_EQ(200, fm.GetLayoutViewport().X());
+  EXPECT_EQ(250, fm.GetLayoutViewport().Y());
+
+  // Case 5 - visual viewport crosses the right boundary of the layout viewport.
+  Pan(apzc, ScreenIntPoint(350, 10), ScreenIntPoint(150, 10),
+      PanOptions::NoFling);
+  fm = apzc->GetFrameMetrics();
+  // It starts from (200, 250) pans by (200, 0) screen pixels, but there is a
+  // 2x zoom, which causes the scroll offset to change by half of that
+  // (100, 0). The visual viewport crossed the right boundary of the layout
+  // viewport by 50px.
+  EXPECT_EQ(300, fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(250, fm.GetVisualScrollOffset().y);
+  EXPECT_EQ(250, fm.GetLayoutViewport().X());
+  EXPECT_EQ(250, fm.GetLayoutViewport().Y());
+
+  // Case 6 - visual viewport crosses both the vertical and horizontal
+  // boundaries of the layout viewport by moving diagonally towards the
+  // top-right corner.
+  Pan(apzc, ScreenIntPoint(350, 200), ScreenIntPoint(150, 400),
+      PanOptions::NoFling);
+  fm = apzc->GetFrameMetrics();
+  // It starts from (300, 250) pans by (200, -200) screen pixels, but there is
+  // a 2x zoom, which causes the scroll offset to change by half of that
+  // (100, -100). The visual viewport moved by (100, -100) outside the
+  // boundary of the layout viewport.
+  EXPECT_EQ(400, fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(150, fm.GetVisualScrollOffset().y);
+  EXPECT_EQ(350, fm.GetLayoutViewport().X());
+  EXPECT_EQ(150, fm.GetLayoutViewport().Y());
+}
+
+TEST_F(APZCPinchGestureDetectorTester, Pinch_APZZoom_Disabled) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_zooming", false);
+
+  FrameMetrics originalMetrics = GetPinchableFrameMetrics();
+  apzc->SetFrameMetrics(originalMetrics);
+
+  // When apz_allow_zooming is false, the ZoomConstraintsClient produces
+  // ZoomConstraints with mAllowZoom set to false.
+  MakeApzcUnzoomable();
+
+  // With apz_allow_zooming false, we expect the NotifyPinchGesture function to
+  // get called as the pinch progresses, but the metrics shouldn't change.
+  EXPECT_CALL(*mcc,
+              NotifyPinchGesture(PinchGestureInput::PINCHGESTURE_START,
+                                 apzc->GetGuid(), _, LayoutDeviceCoord(0), _))
+      .Times(1);
+  EXPECT_CALL(*mcc, NotifyPinchGesture(PinchGestureInput::PINCHGESTURE_SCALE,
+                                       apzc->GetGuid(), _, _, _))
+      .Times(AtLeast(1));
+  EXPECT_CALL(*mcc,
+              NotifyPinchGesture(PinchGestureInput::PINCHGESTURE_END,
+                                 apzc->GetGuid(), _, LayoutDeviceCoord(0), _))
+      .Times(1);
+
+  int touchInputId = 0;
+  uint64_t blockId = 0;
+  PinchWithTouchInput(apzc, ScreenIntPoint(250, 300), 1.25, touchInputId,
+                      nullptr, nullptr, &blockId);
+
+  // verify the metrics didn't change (i.e. the pinch was ignored inside APZ)
+  FrameMetrics fm = apzc->GetFrameMetrics();
+  EXPECT_EQ(originalMetrics.GetZoom(), fm.GetZoom());
+  EXPECT_EQ(originalMetrics.GetVisualScrollOffset().x,
+            fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(originalMetrics.GetVisualScrollOffset().y,
+            fm.GetVisualScrollOffset().y);
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCPinchGestureDetectorTester, Pinch_NoSpan) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_zooming", false);
+
+  FrameMetrics originalMetrics = GetPinchableFrameMetrics();
+  apzc->SetFrameMetrics(originalMetrics);
+
+  // When apz_allow_zooming is false, the ZoomConstraintsClient produces
+  // ZoomConstraints with mAllowZoom set to false.
+  MakeApzcUnzoomable();
+
+  // With apz_allow_zooming false, we expect the NotifyPinchGesture function to
+  // get called as the pinch progresses, but the metrics shouldn't change.
+  EXPECT_CALL(*mcc,
+              NotifyPinchGesture(PinchGestureInput::PINCHGESTURE_START,
+                                 apzc->GetGuid(), _, LayoutDeviceCoord(0), _))
+      .Times(1);
+  EXPECT_CALL(*mcc, NotifyPinchGesture(PinchGestureInput::PINCHGESTURE_SCALE,
+                                       apzc->GetGuid(), _, _, _))
+      .Times(AtLeast(1));
+  EXPECT_CALL(*mcc,
+              NotifyPinchGesture(PinchGestureInput::PINCHGESTURE_END,
+                                 apzc->GetGuid(), _, LayoutDeviceCoord(0), _))
+      .Times(1);
+
+  int inputId = 0;
+  ScreenIntPoint focus(250, 300);
+
+  // Do a pinch holding a zero span and moving the focus by y=100
+
+  const TimeDuration TIME_BETWEEN_TOUCH_EVENT =
+      TimeDuration::FromMilliseconds(50);
+  const auto touchBehaviors = Some(nsTArray<uint32_t>{kDefaultTouchBehavior});
+
+  MultiTouchInput mtiStart =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_START, 0, mcc->Time(), 0);
+  mtiStart.mTouches.AppendElement(CreateSingleTouchData(inputId, focus));
+  mtiStart.mTouches.AppendElement(CreateSingleTouchData(inputId + 1, focus));
+  apzc->ReceiveInputEvent(mtiStart, touchBehaviors);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  focus.y -= 35 + 1;  // this is to get over the PINCH_START_THRESHOLD in
+                      // GestureEventListener.cpp
+  MultiTouchInput mtiMove1 =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mtiMove1.mTouches.AppendElement(CreateSingleTouchData(inputId, focus));
+  mtiMove1.mTouches.AppendElement(CreateSingleTouchData(inputId + 1, focus));
+  apzc->ReceiveInputEvent(mtiMove1);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  focus.y -= 100;  // do a two-finger scroll of 100 screen pixels
+  MultiTouchInput mtiMove2 =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_MOVE, 0, mcc->Time(), 0);
+  mtiMove2.mTouches.AppendElement(CreateSingleTouchData(inputId, focus));
+  mtiMove2.mTouches.AppendElement(CreateSingleTouchData(inputId + 1, focus));
+  apzc->ReceiveInputEvent(mtiMove2);
+  mcc->AdvanceBy(TIME_BETWEEN_TOUCH_EVENT);
+
+  MultiTouchInput mtiEnd =
+      MultiTouchInput(MultiTouchInput::MULTITOUCH_END, 0, mcc->Time(), 0);
+  mtiEnd.mTouches.AppendElement(CreateSingleTouchData(inputId, focus));
+  mtiEnd.mTouches.AppendElement(CreateSingleTouchData(inputId + 1, focus));
+  apzc->ReceiveInputEvent(mtiEnd);
+
+  // Done, check the metrics to make sure we scrolled by 100 screen pixels,
+  // which is 50 CSS pixels for the pinchable frame metrics.
+
+  FrameMetrics fm = apzc->GetFrameMetrics();
+  EXPECT_EQ(originalMetrics.GetZoom(), fm.GetZoom());
+  EXPECT_EQ(originalMetrics.GetVisualScrollOffset().x,
+            fm.GetVisualScrollOffset().x);
+  EXPECT_EQ(originalMetrics.GetVisualScrollOffset().y + 50,
+            fm.GetVisualScrollOffset().y);
+
+  apzc->AssertStateIsReset();
+}
+
+TEST_F(APZCPinchTester, Pinch_TwoFinger_APZZoom_Disabled_Bug1354185) {
+  // Set up APZ such that mZoomConstraints.mAllowZoom is false.
+  SCOPED_GFX_PREF_BOOL("apz.allow_zooming", false);
+  apzc->SetFrameMetrics(GetPinchableFrameMetrics());
+  MakeApzcUnzoomable();
+
+  // We expect a repaint request for scrolling.
+  EXPECT_CALL(*mcc, RequestContentRepaint(_)).Times(1);
+
+  // Send only the PINCHGESTURE_START and PINCHGESTURE_SCALE events,
+  // in order to trigger a call to AsyncPanZoomController::OnScale
+  // but not to AsyncPanZoomController::OnScaleEnd.
+  ScreenIntPoint aFocus(250, 350);
+  ScreenIntPoint aSecondFocus(200, 300);
+  float aScale = 10;
+  auto event = CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_START,
+                                       aFocus, 10.0, 10.0, mcc->Time());
+  apzc->ReceiveInputEvent(event);
+
+  event =
+      CreatePinchGestureInput(PinchGestureInput::PINCHGESTURE_SCALE,
+                              aSecondFocus, 10.0f * aScale, 10.0, mcc->Time());
+  apzc->ReceiveInputEvent(event);
+}
+
+TEST_F(APZCPinchLockingTester, Pinch_Locking_Free) {
+  SCOPED_GFX_PREF_INT("apz.pinch_lock.mode", 0);  // PINCH_FREE
+
+  twoFingerPan();
+  EXPECT_FALSE(isPinchLockActive());
+}
+
+TEST_F(APZCPinchLockingTester, Pinch_Locking_Normal_Lock) {
+  SCOPED_GFX_PREF_INT("apz.pinch_lock.mode", 1);  // PINCH_NORMAL
+
+  twoFingerPan();
+  EXPECT_TRUE(isPinchLockActive());
+}
+
+TEST_F(APZCPinchLockingTester, Pinch_Locking_Normal_Lock_Break) {
+  SCOPED_GFX_PREF_INT("apz.pinch_lock.mode", 1);  // PINCH_NORMAL
+
+  twoFingerPan();
+  twoFingerZoom();
+  EXPECT_TRUE(isPinchLockActive());
+}
+
+TEST_F(APZCPinchLockingTester, Pinch_Locking_Sticky_Lock) {
+  SCOPED_GFX_PREF_INT("apz.pinch_lock.mode", 2);  // PINCH_STICKY
+
+  twoFingerPan();
+  EXPECT_TRUE(isPinchLockActive());
+}
+
+TEST_F(APZCPinchLockingTester, Pinch_Locking_Sticky_Lock_Break) {
+  SCOPED_GFX_PREF_INT("apz.pinch_lock.mode", 2);  // PINCH_STICKY
+
+  twoFingerPan();
+  twoFingerZoom();
+  EXPECT_FALSE(isPinchLockActive());
+}
+
+TEST_F(APZCPinchLockingTester, Pinch_Locking_Sticky_Lock_Break_Lock) {
+  SCOPED_GFX_PREF_INT("apz.pinch_lock.mode", 2);  // PINCH_STICKY
+
+  twoFingerPan();
+  twoFingerZoom();
+  twoFingerPan();
+  EXPECT_TRUE(isPinchLockActive());
+}
diff --git a/gfx/layers/apz/test/gtest/TestScrollHandoff.cpp b/gfx/layers/apz/test/gtest/TestScrollHandoff.cpp
new file mode 100644
index 0000000000..8f497dabe6
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestScrollHandoff.cpp
@@ -0,0 +1,809 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+
+class APZScrollHandoffTester : public APZCTreeManagerTester {
+ protected:
+  UniquePtr<ScopedLayerTreeRegistration> registration;
+  TestAsyncPanZoomController* rootApzc;
+
+  void CreateScrollHandoffLayerTree1() {
+    const char* treeShape = "x(x)";
+    LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                           LayerIntRect(0, 50, 100, 50)};
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 200, 200));
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1,
+                              CSSRect(0, 0, 100, 100));
+    SetScrollHandoff(layers[1], root);
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+    rootApzc = ApzcOf(root);
+    rootApzc->GetFrameMetrics().SetIsRootContent(
+        true);  // make root APZC zoomable
+  }
+
+  void CreateScrollHandoffLayerTree2() {
+    const char* treeShape = "x(x(x))";
+    LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                           LayerIntRect(0, 0, 100, 100),
+                                           LayerIntRect(0, 50, 100, 50)};
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 200, 200));
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 2,
+                              CSSRect(-100, -100, 200, 200));
+    SetScrollableFrameMetrics(layers[2],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1,
+                              CSSRect(0, 0, 100, 100));
+    SetScrollHandoff(layers[1], root);
+    SetScrollHandoff(layers[2], layers[1]);
+    // No ScopedLayerTreeRegistration as that just needs to be done once per
+    // test and this is the second layer tree for a particular test.
+    MOZ_ASSERT(registration);
+    UpdateHitTestingTree();
+    rootApzc = ApzcOf(root);
+  }
+
+  void CreateScrollHandoffLayerTree3() {
+    const char* treeShape = "x(x(x)x(x))";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 100, 100),  // root
+        LayerIntRect(0, 0, 100, 50),   // scrolling parent 1
+        LayerIntRect(0, 0, 100, 50),   // scrolling child 1
+        LayerIntRect(0, 50, 100, 50),  // scrolling parent 2
+        LayerIntRect(0, 50, 100, 50)   // scrolling child 2
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(layers[0], ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 100, 100));
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1,
+                              CSSRect(0, 0, 100, 100));
+    SetScrollableFrameMetrics(layers[2],
+                              ScrollableLayerGuid::START_SCROLL_ID + 2,
+                              CSSRect(0, 0, 100, 100));
+    SetScrollableFrameMetrics(layers[3],
+                              ScrollableLayerGuid::START_SCROLL_ID + 3,
+                              CSSRect(0, 50, 100, 100));
+    SetScrollableFrameMetrics(layers[4],
+                              ScrollableLayerGuid::START_SCROLL_ID + 4,
+                              CSSRect(0, 50, 100, 100));
+    SetScrollHandoff(layers[1], layers[0]);
+    SetScrollHandoff(layers[3], layers[0]);
+    SetScrollHandoff(layers[2], layers[1]);
+    SetScrollHandoff(layers[4], layers[3]);
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+  }
+
+  // Creates a layer tree with a parent layer that is only scrollable
+  // horizontally, and a child layer that is only scrollable vertically.
+  void CreateScrollHandoffLayerTree4() {
+    const char* treeShape = "x(x)";
+    LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                           LayerIntRect(0, 0, 100, 100)};
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 200, 100));
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1,
+                              CSSRect(0, 0, 100, 200));
+    SetScrollHandoff(layers[1], root);
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+    rootApzc = ApzcOf(root);
+  }
+
+  // Creates a layer tree with a parent layer that is not scrollable, and a
+  // child layer that is only scrollable vertically.
+  void CreateScrollHandoffLayerTree5() {
+    const char* treeShape = "x(x)";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 100, 100),  // scrolling parent
+        LayerIntRect(0, 50, 100, 50)   // scrolling child
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 100, 100));
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1,
+                              CSSRect(0, 0, 100, 200));
+    SetScrollHandoff(layers[1], root);
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+    rootApzc = ApzcOf(root);
+  }
+
+  void CreateScrollgrabLayerTree(bool makeParentScrollable = true) {
+    const char* treeShape = "x(x)";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 100, 100),  // scroll-grabbing parent
+        LayerIntRect(0, 20, 100, 80)   // child
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    float parentHeight = makeParentScrollable ? 120 : 100;
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 100, parentHeight));
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1,
+                              CSSRect(0, 0, 100, 800));
+    SetScrollHandoff(layers[1], root);
+    registration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+    UpdateHitTestingTree();
+    rootApzc = ApzcOf(root);
+    rootApzc->GetScrollMetadata().SetHasScrollgrab(true);
+  }
+
+  void TestFlingAcceleration() {
+    // Jack up the fling acceleration multiplier so we can easily determine
+    // whether acceleration occured.
+    const float kAcceleration = 100.0f;
+    SCOPED_GFX_PREF_FLOAT("apz.fling_accel_base_mult", kAcceleration);
+    SCOPED_GFX_PREF_FLOAT("apz.fling_accel_min_fling_velocity", 0.0);
+    SCOPED_GFX_PREF_FLOAT("apz.fling_accel_min_pan_velocity", 0.0);
+
+    RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+    // Pan once, enough to fully scroll the scrollgrab parent and then scroll
+    // and fling the child.
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+    Pan(manager, 70, 40);
+
+    // Give the fling animation a chance to start.
+    SampleAnimationsOnce();
+
+    float childVelocityAfterFling1 = childApzc->GetVelocityVector().y;
+
+    // Pan again.
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+    Pan(manager, 70, 40);
+
+    // Give the fling animation a chance to start.
+    // This time it should be accelerated.
+    SampleAnimationsOnce();
+
+    float childVelocityAfterFling2 = childApzc->GetVelocityVector().y;
+
+    // We should have accelerated once.
+    // The division by 2 is to account for friction.
+    EXPECT_GT(childVelocityAfterFling2,
+              childVelocityAfterFling1 * kAcceleration / 2);
+
+    // We should not have accelerated twice.
+    // The division by 4 is to account for friction.
+    EXPECT_LE(childVelocityAfterFling2,
+              childVelocityAfterFling1 * kAcceleration * kAcceleration / 4);
+  }
+
+  void TestCrossApzcAxisLock() {
+    SCOPED_GFX_PREF_INT("apz.axis_lock.mode", 1);
+
+    CreateScrollHandoffLayerTree1();
+
+    RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+    Pan(childApzc, ScreenIntPoint(10, 60), ScreenIntPoint(15, 90),
+        PanOptions::KeepFingerDown | PanOptions::ExactCoordinates);
+
+    childApzc->AssertAxisLocked(ScrollDirection::eVertical);
+    childApzc->AssertStateIsPanningLockedY();
+  }
+};
+
+class APZScrollHandoffTesterMock : public APZScrollHandoffTester {
+ public:
+  APZScrollHandoffTesterMock() { CreateMockHitTester(); }
+};
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+// Here we test that if the processing of a touch block is deferred while we
+// wait for content to send a prevent-default message, overscroll is still
+// handed off correctly when the block is processed.
+TEST_F(APZScrollHandoffTester, DeferredInputEventProcessing) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", true);
+
+  // Set up the APZC tree.
+  CreateScrollHandoffLayerTree1();
+
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  // Enable touch-listeners so that we can separate the queueing of input
+  // events from them being processed.
+  childApzc->SetWaitForMainThread();
+
+  // Queue input events for a pan.
+  uint64_t blockId = 0;
+  Pan(childApzc, 90, 30, PanOptions::NoFling, nullptr, nullptr, &blockId);
+
+  // Allow the pan to be processed.
+  childApzc->ContentReceivedInputBlock(blockId, false);
+  childApzc->ConfirmTarget(blockId);
+
+  // Make sure overscroll was handed off correctly.
+  EXPECT_EQ(50, childApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+  EXPECT_EQ(10, rootApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+// Here we test that if the layer structure changes in between two input
+// blocks being queued, and the first block is only processed after the second
+// one has been queued, overscroll handoff for the first block follows
+// the original layer structure while overscroll handoff for the second block
+// follows the new layer structure.
+TEST_F(APZScrollHandoffTester, LayerStructureChangesWhileEventsArePending) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", true);
+
+  // Set up an initial APZC tree.
+  CreateScrollHandoffLayerTree1();
+
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  // Enable touch-listeners so that we can separate the queueing of input
+  // events from them being processed.
+  childApzc->SetWaitForMainThread();
+
+  // Queue input events for a pan.
+  uint64_t blockId = 0;
+  Pan(childApzc, 90, 30, PanOptions::NoFling, nullptr, nullptr, &blockId);
+
+  // Modify the APZC tree to insert a new APZC 'middle' into the handoff chain
+  // between the child and the root.
+  CreateScrollHandoffLayerTree2();
+  WebRenderLayerScrollData* middle = layers[1];
+  childApzc->SetWaitForMainThread();
+  TestAsyncPanZoomController* middleApzc = ApzcOf(middle);
+
+  // Queue input events for another pan.
+  uint64_t secondBlockId = 0;
+  Pan(childApzc, 30, 90, PanOptions::NoFling, nullptr, nullptr, &secondBlockId);
+
+  // Allow the first pan to be processed.
+  childApzc->ContentReceivedInputBlock(blockId, false);
+  childApzc->ConfirmTarget(blockId);
+
+  // Make sure things have scrolled according to the handoff chain in
+  // place at the time the touch-start of the first pan was queued.
+  EXPECT_EQ(50, childApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+  EXPECT_EQ(10, rootApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+  EXPECT_EQ(0, middleApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+
+  // Allow the second pan to be processed.
+  childApzc->ContentReceivedInputBlock(secondBlockId, false);
+  childApzc->ConfirmTarget(secondBlockId);
+
+  // Make sure things have scrolled according to the handoff chain in
+  // place at the time the touch-start of the second pan was queued.
+  EXPECT_EQ(0, childApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+  EXPECT_EQ(10, rootApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+  EXPECT_EQ(-10, middleApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+// Test that putting a second finger down on an APZC while a down-chain APZC
+// is overscrolled doesn't result in being stuck in overscroll.
+TEST_F(APZScrollHandoffTesterMock, StuckInOverscroll_Bug1073250) {
+  // Enable overscrolling.
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  CreateScrollHandoffLayerTree1();
+
+  TestAsyncPanZoomController* child = ApzcOf(layers[1]);
+
+  // Pan, causing the parent APZC to overscroll.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  Pan(manager, 10, 40, PanOptions::KeepFingerDown);
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+
+  // Put a second finger down.
+  MultiTouchInput secondFingerDown =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  // Use the same touch identifier for the first touch (0) as Pan(). (A bit
+  // hacky.)
+  secondFingerDown.mTouches.AppendElement(
+      SingleTouchData(0, ScreenIntPoint(10, 40), ScreenSize(0, 0), 0, 0));
+  secondFingerDown.mTouches.AppendElement(
+      SingleTouchData(1, ScreenIntPoint(30, 20), ScreenSize(0, 0), 0, 0));
+  manager->ReceiveInputEvent(secondFingerDown);
+
+  // Release the fingers.
+  MultiTouchInput fingersUp = secondFingerDown;
+  fingersUp.mType = MultiTouchInput::MULTITOUCH_END;
+  manager->ReceiveInputEvent(fingersUp);
+
+  // Allow any animations to run their course.
+  child->AdvanceAnimationsUntilEnd();
+  rootApzc->AdvanceAnimationsUntilEnd();
+
+  // Make sure nothing is overscrolled.
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+// This is almost exactly like StuckInOverscroll_Bug1073250, except the
+// APZC receiving the input events for the first touch block is the child
+// (and thus not the same APZC that overscrolls, which is the parent).
+TEST_F(APZScrollHandoffTesterMock, StuckInOverscroll_Bug1231228) {
+  // Enable overscrolling.
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  CreateScrollHandoffLayerTree1();
+
+  TestAsyncPanZoomController* child = ApzcOf(layers[1]);
+
+  // Pan, causing the parent APZC to overscroll.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  Pan(manager, 60, 90, PanOptions::KeepFingerDown);
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+
+  // Put a second finger down.
+  MultiTouchInput secondFingerDown =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  // Use the same touch identifier for the first touch (0) as Pan(). (A bit
+  // hacky.)
+  secondFingerDown.mTouches.AppendElement(
+      SingleTouchData(0, ScreenIntPoint(10, 40), ScreenSize(0, 0), 0, 0));
+  secondFingerDown.mTouches.AppendElement(
+      SingleTouchData(1, ScreenIntPoint(30, 20), ScreenSize(0, 0), 0, 0));
+  manager->ReceiveInputEvent(secondFingerDown);
+
+  // Release the fingers.
+  MultiTouchInput fingersUp = secondFingerDown;
+  fingersUp.mType = MultiTouchInput::MULTITOUCH_END;
+  manager->ReceiveInputEvent(fingersUp);
+
+  // Allow any animations to run their course.
+  child->AdvanceAnimationsUntilEnd();
+  rootApzc->AdvanceAnimationsUntilEnd();
+
+  // Make sure nothing is overscrolled.
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZScrollHandoffTester, StuckInOverscroll_Bug1240202a) {
+  // Enable overscrolling.
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  CreateScrollHandoffLayerTree1();
+
+  TestAsyncPanZoomController* child = ApzcOf(layers[1]);
+
+  // Pan, causing the parent APZC to overscroll.
+  Pan(manager, 60, 90, PanOptions::KeepFingerDown);
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+
+  // Lift the finger, triggering an overscroll animation
+  // (but don't allow it to run).
+  TouchUp(manager, ScreenIntPoint(10, 90), mcc->Time());
+
+  // Put the finger down again, interrupting the animation
+  // and entering the TOUCHING state.
+  TouchDown(manager, ScreenIntPoint(10, 90), mcc->Time());
+
+  // Lift the finger once again.
+  TouchUp(manager, ScreenIntPoint(10, 90), mcc->Time());
+
+  // Allow any animations to run their course.
+  child->AdvanceAnimationsUntilEnd();
+  rootApzc->AdvanceAnimationsUntilEnd();
+
+  // Make sure nothing is overscrolled.
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZScrollHandoffTesterMock, StuckInOverscroll_Bug1240202b) {
+  // Enable overscrolling.
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  CreateScrollHandoffLayerTree1();
+
+  TestAsyncPanZoomController* child = ApzcOf(layers[1]);
+
+  // Pan, causing the parent APZC to overscroll.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  Pan(manager, 60, 90, PanOptions::KeepFingerDown);
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_TRUE(rootApzc->IsOverscrolled());
+
+  // Lift the finger, triggering an overscroll animation
+  // (but don't allow it to run).
+  TouchUp(manager, ScreenIntPoint(10, 90), mcc->Time());
+
+  // Put the finger down again, interrupting the animation
+  // and entering the TOUCHING state.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  TouchDown(manager, ScreenIntPoint(10, 90), mcc->Time());
+
+  // Put a second finger down. Since we're in the TOUCHING state,
+  // the "are we panned into overscroll" check will fail and we
+  // will not ignore the second finger, instead entering the
+  // PINCHING state.
+  MultiTouchInput secondFingerDown(MultiTouchInput::MULTITOUCH_START, 0,
+                                   TimeStamp(), 0);
+  // Use the same touch identifier for the first touch (0) as TouchDown(). (A
+  // bit hacky.)
+  secondFingerDown.mTouches.AppendElement(
+      SingleTouchData(0, ScreenIntPoint(10, 90), ScreenSize(0, 0), 0, 0));
+  secondFingerDown.mTouches.AppendElement(
+      SingleTouchData(1, ScreenIntPoint(10, 80), ScreenSize(0, 0), 0, 0));
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  manager->ReceiveInputEvent(secondFingerDown);
+
+  // Release the fingers.
+  MultiTouchInput fingersUp = secondFingerDown;
+  fingersUp.mType = MultiTouchInput::MULTITOUCH_END;
+  manager->ReceiveInputEvent(fingersUp);
+
+  // Allow any animations to run their course.
+  child->AdvanceAnimationsUntilEnd();
+  rootApzc->AdvanceAnimationsUntilEnd();
+
+  // Make sure nothing is overscrolled.
+  EXPECT_FALSE(child->IsOverscrolled());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+}
+#endif
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZScrollHandoffTester, OpposingConstrainedAxes_Bug1201098) {
+  // Enable overscrolling.
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  CreateScrollHandoffLayerTree4();
+
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  // Pan, causing the child APZC to overscroll.
+  Pan(childApzc, 50, 60);
+
+  // Make sure only the child is overscrolled.
+  EXPECT_TRUE(childApzc->IsOverscrolled());
+  EXPECT_FALSE(rootApzc->IsOverscrolled());
+}
+#endif
+
+// Test that flinging in a direction where one component of the fling goes into
+// overscroll but the other doesn't, results in just the one component being
+// handed off to the parent, while the original APZC continues flinging in the
+// other direction.
+TEST_F(APZScrollHandoffTesterMock, PartialFlingHandoff) {
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  CreateScrollHandoffLayerTree1();
+
+  // Fling up and to the left. The child APZC has room to scroll up, but not
+  // to the left, so the horizontal component of the fling should be handed
+  // off to the parent APZC.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  Pan(manager, ScreenIntPoint(90, 90), ScreenIntPoint(55, 55));
+
+  RefPtr<TestAsyncPanZoomController> parent = ApzcOf(layers[0]);
+  RefPtr<TestAsyncPanZoomController> child = ApzcOf(layers[1]);
+
+  // Advance the child's fling animation once to give the partial handoff
+  // a chance to occur.
+  mcc->AdvanceByMillis(10);
+  child->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Assert that partial handoff has occurred.
+  child->AssertStateIsFling();
+  parent->AssertStateIsFling();
+}
+
+// Here we test that if two flings are happening simultaneously, overscroll
+// is handed off correctly for each.
+TEST_F(APZScrollHandoffTester, SimultaneousFlings) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", true);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  // Set up an initial APZC tree.
+  CreateScrollHandoffLayerTree3();
+
+  RefPtr<TestAsyncPanZoomController> parent1 = ApzcOf(layers[1]);
+  RefPtr<TestAsyncPanZoomController> child1 = ApzcOf(layers[2]);
+  RefPtr<TestAsyncPanZoomController> parent2 = ApzcOf(layers[3]);
+  RefPtr<TestAsyncPanZoomController> child2 = ApzcOf(layers[4]);
+
+  // Pan on the lower child.
+  Pan(child2, 45, 5);
+
+  // Pan on the upper child.
+  Pan(child1, 95, 55);
+
+  // Check that child1 and child2 are in a FLING state.
+  child1->AssertStateIsFling();
+  child2->AssertStateIsFling();
+
+  // Advance the animations on child1 and child2 until their end.
+  child1->AdvanceAnimationsUntilEnd();
+  child2->AdvanceAnimationsUntilEnd();
+
+  // Check that the flings have been handed off to the parents.
+  child1->AssertStateIsReset();
+  parent1->AssertStateIsFling();
+  child2->AssertStateIsReset();
+  parent2->AssertStateIsFling();
+}
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZScrollHandoffTester, Scrollgrab) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", true);
+
+  // Set up the layer tree
+  CreateScrollgrabLayerTree();
+
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  // Pan on the child, enough to fully scroll the scrollgrab parent (20 px)
+  // and leave some more (another 15 px) for the child.
+  Pan(childApzc, 80, 45);
+
+  // Check that the parent and child have scrolled as much as we expect.
+  EXPECT_EQ(20, rootApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+  EXPECT_EQ(15, childApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+}
+#endif
+
+TEST_F(APZScrollHandoffTester, ScrollgrabFling) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", true);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  // Set up the layer tree
+  CreateScrollgrabLayerTree();
+
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  // Pan on the child, not enough to fully scroll the scrollgrab parent.
+  Pan(childApzc, 80, 70);
+
+  // Check that it is the scrollgrab parent that's in a fling, not the child.
+  rootApzc->AssertStateIsFling();
+  childApzc->AssertStateIsReset();
+}
+
+TEST_F(APZScrollHandoffTesterMock, ScrollgrabFlingAcceleration1) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", true);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+  CreateScrollgrabLayerTree(true /* make parent scrollable */);
+
+  // Note: Usually, fling acceleration does not work across handoff, because our
+  // fling acceleration code does not propagate the "fling cancel velocity"
+  // across handoff. However, this test sets apz.fling_min_velocity_threshold to
+  // zero, so the "fling cancel velocity" is allowed to be zero, and fling
+  // acceleration succeeds, almost by accident.
+  TestFlingAcceleration();
+}
+
+TEST_F(APZScrollHandoffTesterMock, ScrollgrabFlingAcceleration2) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", true);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+  CreateScrollgrabLayerTree(false /* do not make parent scrollable */);
+  TestFlingAcceleration();
+}
+
+TEST_F(APZScrollHandoffTester, ImmediateHandoffDisallowed_Pan) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", false);
+
+  CreateScrollHandoffLayerTree1();
+
+  RefPtr<TestAsyncPanZoomController> parentApzc = ApzcOf(layers[0]);
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  // Pan on the child, enough to scroll it to its end and have scroll
+  // left to hand off. Since immediate handoff is disallowed, we expect
+  // the leftover scroll not to be handed off.
+  Pan(childApzc, 60, 5);
+
+  // Verify that the parent has not scrolled.
+  EXPECT_EQ(50, childApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+  EXPECT_EQ(0, parentApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+
+  // Pan again on the child. This time, since the child was scrolled to
+  // its end when the gesture began, we expect the scroll to be handed off.
+  Pan(childApzc, 60, 50);
+
+  // Verify that the parent scrolled.
+  EXPECT_EQ(10, parentApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+}
+
+TEST_F(APZScrollHandoffTester, ImmediateHandoffDisallowed_Fling) {
+  SCOPED_GFX_PREF_BOOL("apz.allow_immediate_handoff", false);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_min_velocity_threshold", 0.0f);
+
+  CreateScrollHandoffLayerTree1();
+
+  RefPtr<TestAsyncPanZoomController> parentApzc = ApzcOf(layers[0]);
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  // Pan on the child, enough to get very close to the end, so that the
+  // subsequent fling reaches the end and has leftover velocity to hand off.
+  Pan(childApzc, 60, 2);
+
+  // Allow the fling to run its course.
+  childApzc->AdvanceAnimationsUntilEnd();
+  parentApzc->AdvanceAnimationsUntilEnd();
+
+  // Verify that the parent has not scrolled.
+  // The first comparison needs to be an ASSERT_NEAR because the fling
+  // computations are such that the final scroll position can be within
+  // COORDINATE_EPSILON of the end rather than right at the end.
+  ASSERT_NEAR(50, childApzc->GetFrameMetrics().GetVisualScrollOffset().y,
+              COORDINATE_EPSILON);
+  EXPECT_EQ(0, parentApzc->GetFrameMetrics().GetVisualScrollOffset().y);
+
+  // Pan again on the child. This time, since the child was scrolled to
+  // its end when the gesture began, we expect the scroll to be handed off.
+  Pan(childApzc, 60, 40);
+
+  // Allow the fling to run its course. The fling should also be handed off.
+  childApzc->AdvanceAnimationsUntilEnd();
+  parentApzc->AdvanceAnimationsUntilEnd();
+
+  // Verify that the parent scrolled from the fling.
+  EXPECT_GT(parentApzc->GetFrameMetrics().GetVisualScrollOffset().y, 10);
+}
+
+TEST_F(APZScrollHandoffTester, CrossApzcAxisLock_TouchAction) {
+  TestCrossApzcAxisLock();
+}
+
+TEST_F(APZScrollHandoffTesterMock, WheelHandoffAfterDirectionReversal) {
+  // Explicitly set the wheel transaction timeout pref because the test relies
+  // on its value.
+  SCOPED_GFX_PREF_INT("mousewheel.transaction.timeout", 1500);
+
+  // Set up a basic scroll handoff layer tree.
+  CreateScrollHandoffLayerTree1();
+
+  rootApzc = ApzcOf(layers[0]);
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+  FrameMetrics& rootMetrics = rootApzc->GetFrameMetrics();
+  FrameMetrics& childMetrics = childApzc->GetFrameMetrics();
+  CSSRect childScrollRange = childMetrics.CalculateScrollRange();
+
+  EXPECT_EQ(0, rootMetrics.GetVisualScrollOffset().y);
+  EXPECT_EQ(0, childMetrics.GetVisualScrollOffset().y);
+
+  ScreenIntPoint cursorLocation(10, 60);  // positioned to hit the subframe
+  ScreenPoint upwardDelta(0, -10);
+  ScreenPoint downwardDelta(0, 10);
+
+  // First wheel upwards. This will have no effect because we're already
+  // scrolled to the top.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  Wheel(manager, cursorLocation, upwardDelta, mcc->Time());
+  EXPECT_EQ(0, rootMetrics.GetVisualScrollOffset().y);
+  EXPECT_EQ(0, childMetrics.GetVisualScrollOffset().y);
+
+  // Now wheel downwards 6 times. This should scroll the child, and get it
+  // to the bottom of its 50px scroll range.
+  for (size_t i = 0; i < 6; ++i) {
+    mcc->AdvanceByMillis(100);
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+    Wheel(manager, cursorLocation, downwardDelta, mcc->Time());
+  }
+  EXPECT_EQ(0, rootMetrics.GetVisualScrollOffset().y);
+  EXPECT_EQ(childScrollRange.YMost(), childMetrics.GetVisualScrollOffset().y);
+
+  // Wheel downwards an additional 16 times, with 100ms increments.
+  // This should be enough to overcome the 1500ms wheel transaction timeout
+  // and start scrolling the root.
+  for (size_t i = 0; i < 16; ++i) {
+    mcc->AdvanceByMillis(100);
+    QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+    Wheel(manager, cursorLocation, downwardDelta, mcc->Time());
+  }
+  EXPECT_EQ(childScrollRange.YMost(), childMetrics.GetVisualScrollOffset().y);
+  EXPECT_GT(rootMetrics.GetVisualScrollOffset().y, 0);
+}
+
+TEST_F(APZScrollHandoffTesterMock, WheelHandoffNonscrollable) {
+  // Set up a basic scroll layer tree.
+  CreateScrollHandoffLayerTree5();
+
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+  FrameMetrics& childMetrics = childApzc->GetFrameMetrics();
+
+  EXPECT_EQ(0, childMetrics.GetVisualScrollOffset().y);
+
+  ScreenPoint downwardDelta(0, 10);
+  // Positioned to hit the nonscrollable parent frame
+  ScreenIntPoint nonscrollableLocation(40, 10);
+  // Positioned to hit the scrollable subframe
+  ScreenIntPoint scrollableLocation(40, 60);
+
+  // Start the wheel transaction on a nonscrollable parent frame.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  Wheel(manager, nonscrollableLocation, downwardDelta, mcc->Time());
+  EXPECT_EQ(0, childMetrics.GetVisualScrollOffset().y);
+
+  // Mouse moves to a scrollable subframe. This should end the transaction.
+  mcc->AdvanceByMillis(100);
+  MouseInput mouseInput(MouseInput::MOUSE_MOVE,
+                        MouseInput::ButtonType::PRIMARY_BUTTON, 0, 0,
+                        scrollableLocation, mcc->Time(), 0);
+  WidgetMouseEvent mouseEvent = mouseInput.ToWidgetEvent(nullptr);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  ((APZInputBridge*)manager.get())->ReceiveInputEvent(mouseEvent);
+
+  // Wheel downward should scroll the subframe.
+  mcc->AdvanceByMillis(100);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  Wheel(manager, scrollableLocation, downwardDelta, mcc->Time());
+  EXPECT_GT(childMetrics.GetVisualScrollOffset().y, 0);
+}
+
+TEST_F(APZScrollHandoffTesterMock, ChildCloseToEndOfScrollRange) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  CreateScrollHandoffLayerTree1();
+
+  RefPtr<TestAsyncPanZoomController> childApzc = ApzcOf(layers[1]);
+
+  FrameMetrics& rootMetrics = rootApzc->GetFrameMetrics();
+  FrameMetrics& childMetrics = childApzc->GetFrameMetrics();
+
+  // Zoom the page in by 3x. This needs to be reflected in the zoom level
+  // and composition bounds of both APZCs.
+  rootMetrics.SetZoom(CSSToParentLayerScale(3.0));
+  rootMetrics.SetCompositionBounds(ParentLayerRect(0, 0, 300, 300));
+  childMetrics.SetZoom(CSSToParentLayerScale(3.0));
+  childMetrics.SetCompositionBounds(ParentLayerRect(0, 150, 300, 150));
+
+  // Scroll the child APZC very close to the end of the scroll range.
+  // The scroll offset is chosen such that in CSS pixels it has 0.01 pixels
+  // room to scroll (less than COORDINATE_EPSILON = 0.02), but in ParentLayer
+  // pixels it has 0.03 pixels room (greater than COORDINATE_EPSILON).
+  childMetrics.SetVisualScrollOffset(CSSPoint(0, 49.99));
+
+  EXPECT_FALSE(childApzc->IsOverscrolled());
+
+  CSSPoint childBefore = childApzc->GetFrameMetrics().GetVisualScrollOffset();
+  CSSPoint parentBefore = rootApzc->GetFrameMetrics().GetVisualScrollOffset();
+
+  // Synthesize a pan gesture that tries to scroll the child further down.
+  PanGesture(PanGestureInput::PANGESTURE_START, childApzc,
+             ScreenIntPoint(10, 20), ScreenPoint(0, 40), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  childApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  PanGesture(PanGestureInput::PANGESTURE_END, childApzc, ScreenIntPoint(10, 21),
+             ScreenPoint(0, 0), mcc->Time());
+
+  CSSPoint childAfter = childApzc->GetFrameMetrics().GetVisualScrollOffset();
+  CSSPoint parentAfter = rootApzc->GetFrameMetrics().GetVisualScrollOffset();
+
+  bool childScrolled = (childBefore != childAfter);
+  bool parentScrolled = (parentBefore != parentAfter);
+
+  // Check that either the child or the parent scrolled.
+  // (With the current implementation of comparing quantities to
+  // COORDINATE_EPSILON in CSS units, it will be the parent, but the important
+  // thing is that at least one of the child or parent scroll, i.e. we're not
+  // stuck in a situation where no scroll offset is changing).
+  EXPECT_TRUE(childScrolled || parentScrolled);
+}
diff --git a/gfx/layers/apz/test/gtest/TestSnapping.cpp b/gfx/layers/apz/test/gtest/TestSnapping.cpp
new file mode 100644
index 0000000000..13bb1e5591
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestSnapping.cpp
@@ -0,0 +1,305 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+
+#include "InputUtils.h"
+#include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/StaticPrefs_mousewheel.h"
+
+class APZCSnappingTesterMock : public APZCTreeManagerTester {
+ public:
+  APZCSnappingTesterMock() { CreateMockHitTester(); }
+};
+
+TEST_F(APZCSnappingTesterMock, Bug1265510) {
+  const char* treeShape = "x(x)";
+  LayerIntRegion layerVisibleRegion[] = {LayerIntRect(0, 0, 100, 100),
+                                         LayerIntRect(0, 100, 100, 100)};
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 200));
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID + 1,
+                            CSSRect(0, 0, 100, 200));
+  SetScrollHandoff(layers[1], root);
+
+  ScrollSnapInfo snap;
+  snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
+  snap.mSnapportSize = CSSSize::ToAppUnits(
+      layerVisibleRegion[0].GetBounds().Size() * LayerToCSSScale(1.0));
+
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(0 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 0, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{1}));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(100 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 100, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{2}));
+
+  ModifyFrameMetrics(root, [&](ScrollMetadata& aSm, FrameMetrics&) {
+    aSm.SetSnapInfo(ScrollSnapInfo(snap));
+  });
+
+  UniquePtr<ScopedLayerTreeRegistration> registration =
+      MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  TestAsyncPanZoomController* outer = ApzcOf(layers[0]);
+  TestAsyncPanZoomController* inner = ApzcOf(layers[1]);
+
+  // Position the mouse near the bottom of the outer frame and scroll by 60px.
+  // (6 lines of 10px each). APZC will actually scroll to y=100 because of the
+  // mandatory snap coordinate there.
+  TimeStamp now = mcc->Time();
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  SmoothWheel(manager, ScreenIntPoint(50, 80), ScreenPoint(0, 6), now);
+  // Advance in 5ms increments until we've scrolled by 70px. At this point, the
+  // closest snap point is y=100, and the inner frame should be under the mouse
+  // cursor.
+  while (outer
+             ->GetCurrentAsyncScrollOffset(
+                 AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting)
+             .y < 70) {
+    mcc->AdvanceByMillis(5);
+    outer->AdvanceAnimations(mcc->GetSampleTime());
+  }
+  // Now do another wheel in a new transaction. This should start scrolling the
+  // inner frame; we verify that it does by checking the inner scroll position.
+  TimeStamp newTransactionTime =
+      now + TimeDuration::FromMilliseconds(
+                StaticPrefs::mousewheel_transaction_timeout() + 100);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  SmoothWheel(manager, ScreenIntPoint(50, 80), ScreenPoint(0, 6),
+              newTransactionTime);
+  inner->AdvanceAnimationsUntilEnd();
+  EXPECT_LT(
+      0.0f,
+      inner
+          ->GetCurrentAsyncScrollOffset(
+              AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting)
+          .y);
+
+  // However, the outer frame should also continue to the snap point, otherwise
+  // it is demonstrating incorrect behaviour by violating the mandatory
+  // snapping.
+  outer->AdvanceAnimationsUntilEnd();
+  EXPECT_EQ(
+      100.0f,
+      outer
+          ->GetCurrentAsyncScrollOffset(
+              AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting)
+          .y);
+}
+
+TEST_F(APZCSnappingTesterMock, Snap_After_Pinch) {
+  const char* treeShape = "x";
+  LayerIntRegion layerVisibleRegion[] = {
+      LayerIntRect(0, 0, 100, 100),
+  };
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 200));
+
+  // Set up some basic scroll snapping
+  ScrollSnapInfo snap;
+  snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
+  snap.mSnapportSize = CSSSize::ToAppUnits(
+      layerVisibleRegion[0].GetBounds().Size() * LayerToCSSScale(1.0));
+
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(0 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 0, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{1}));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(100 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 100, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{2}));
+
+  // Save the scroll snap info on the root APZC.
+  // Also mark the root APZC as "root content", since APZC only allows
+  // zooming on the root content APZC.
+  ModifyFrameMetrics(root, [&](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    aSm.SetSnapInfo(ScrollSnapInfo(snap));
+    aMetrics.SetIsRootContent(true);
+  });
+
+  UniquePtr<ScopedLayerTreeRegistration> registration =
+      MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+
+  // Allow zooming
+  apzc->UpdateZoomConstraints(ZoomConstraints(
+      true, true, CSSToParentLayerScale(0.25f), CSSToParentLayerScale(4.0f)));
+
+  PinchWithPinchInput(apzc, ScreenIntPoint(50, 50), ScreenIntPoint(50, 50),
+                      1.2f);
+
+  apzc->AssertStateIsSmoothMsdScroll();
+}
+
+// Currently fails on Android because on the platform we have a different
+// VelocityTracker.
+#ifndef MOZ_WIDGET_ANDROID
+TEST_F(APZCSnappingTesterMock, SnapOnPanEndWithZeroVelocity) {
+  // Use pref values for desktop everywhere.
+  SCOPED_GFX_PREF_FLOAT("apz.fling_friction", 0.002);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_stopped_threshold", 0.01);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_x1", 0.0);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_x2", 1.0);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_y1", 0.0);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_y2", 1.0);
+  SCOPED_GFX_PREF_INT("apz.velocity_relevance_time_ms", 100);
+
+  const char* treeShape = "x";
+  LayerIntRegion layerVisibleRegion[] = {
+      LayerIntRect(0, 0, 100, 100),
+  };
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 400));
+
+  // Set up two snap points, 30 and 100.
+  ScrollSnapInfo snap;
+  snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
+  snap.mSnapportSize = CSSSize::ToAppUnits(
+      layerVisibleRegion[0].GetBounds().Size() * LayerToCSSScale(1.0));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(30 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 30, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{1}));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(100 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 100, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{2}));
+
+  // Save the scroll snap info on the root APZC.
+  ModifyFrameMetrics(root, [&](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    aSm.SetSnapInfo(ScrollSnapInfo(snap));
+  });
+
+  UniquePtr<ScopedLayerTreeRegistration> registration =
+      MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+
+  // Send a series of pan gestures to scroll to position at 50.
+  const ScreenIntPoint position = ScreenIntPoint(50, 30);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, position,
+             ScreenPoint(0, 10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, position,
+             ScreenPoint(0, 40), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Make sure the velocity just before sending a pan-end is zero.
+  EXPECT_EQ(apzc->GetVelocityVector().y, 0);
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, position,
+             ScreenPoint(0, 0), mcc->Time());
+
+  // Now a smooth animation has been triggered for snapping to 30.
+  apzc->AssertStateIsSmoothMsdScroll();
+
+  apzc->AdvanceAnimationsUntilEnd();
+  // The snapped position should be 30 rather than 100 because it's the nearest
+  // snap point.
+  EXPECT_EQ(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      30);
+}
+
+// Smililar to above SnapOnPanEndWithZeroVelocity but with positive velocity so
+// that the snap position would be the one in the scrolling direction.
+TEST_F(APZCSnappingTesterMock, SnapOnPanEndWithPositiveVelocity) {
+  // Use pref values for desktop everywhere.
+  SCOPED_GFX_PREF_FLOAT("apz.fling_friction", 0.002);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_stopped_threshold", 0.01);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_x1", 0.0);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_x2", 1.0);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_y1", 0.0);
+  SCOPED_GFX_PREF_FLOAT("apz.fling_curve_function_y2", 1.0);
+  SCOPED_GFX_PREF_INT("apz.velocity_relevance_time_ms", 100);
+
+  const char* treeShape = "x";
+  LayerIntRegion layerVisibleRegion[] = {
+      LayerIntRect(0, 0, 100, 100),
+  };
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 400));
+
+  // Set up two snap points, 30 and 100.
+  ScrollSnapInfo snap;
+  snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
+  snap.mSnapportSize = CSSSize::ToAppUnits(
+      layerVisibleRegion[0].GetBounds().Size() * LayerToCSSScale(1.0));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(30 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 30, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{1}));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(100 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 100, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{2}));
+
+  // Save the scroll snap info on the root APZC.
+  ModifyFrameMetrics(root, [&](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    aSm.SetSnapInfo(ScrollSnapInfo(snap));
+  });
+
+  UniquePtr<ScopedLayerTreeRegistration> registration =
+      MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+
+  // Send a series of pan gestures that a pan-end event happens at 65
+  const ScreenIntPoint position = ScreenIntPoint(50, 30);
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, position,
+             ScreenPoint(0, 10), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, position,
+             ScreenPoint(0, 35), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, position,
+             ScreenPoint(0, 20), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // There should be positive velocity in this case.
+  EXPECT_GT(apzc->GetVelocityVector().y, 0);
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, position,
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+
+  // A smooth animation has been triggered by the pan-end event above.
+  apzc->AssertStateIsSmoothMsdScroll();
+
+  apzc->AdvanceAnimationsUntilEnd();
+  EXPECT_EQ(
+      apzc->GetCurrentAsyncScrollOffset(AsyncPanZoomController::eForHitTesting)
+          .y,
+      100);
+}
+#endif
diff --git a/gfx/layers/apz/test/gtest/TestSnappingOnMomentum.cpp b/gfx/layers/apz/test/gtest/TestSnappingOnMomentum.cpp
new file mode 100644
index 0000000000..02b1d6798c
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestSnappingOnMomentum.cpp
@@ -0,0 +1,104 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+
+#include "InputUtils.h"
+#include "mozilla/StaticPrefs_layout.h"
+
+class APZCSnappingOnMomentumTesterMock : public APZCTreeManagerTester {
+ public:
+  APZCSnappingOnMomentumTesterMock() { CreateMockHitTester(); }
+};
+
+TEST_F(APZCSnappingOnMomentumTesterMock, Snap_On_Momentum) {
+  const char* treeShape = "x";
+  LayerIntRegion layerVisibleRegion[] = {
+      LayerIntRect(0, 0, 100, 100),
+  };
+  CreateScrollData(treeShape, layerVisibleRegion);
+  SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                            CSSRect(0, 0, 100, 500));
+
+  // Set up some basic scroll snapping
+  ScrollSnapInfo snap;
+  snap.mScrollSnapStrictnessY = StyleScrollSnapStrictness::Mandatory;
+  snap.mSnapportSize = CSSSize::ToAppUnits(
+      layerVisibleRegion[0].GetBounds().Size() * LayerToCSSScale(1.0));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(0 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 0, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{1}));
+  snap.mSnapTargets.AppendElement(ScrollSnapInfo::SnapTarget(
+      Nothing(), Some(100 * AppUnitsPerCSSPixel()),
+      CSSRect::ToAppUnits(CSSRect(0, 100, 10, 10)), StyleScrollSnapStop::Normal,
+      ScrollSnapTargetId{2}));
+
+  ModifyFrameMetrics(root, [&](ScrollMetadata& aSm, FrameMetrics&) {
+    aSm.SetSnapInfo(ScrollSnapInfo(snap));
+  });
+
+  UniquePtr<ScopedLayerTreeRegistration> registration =
+      MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+
+  TimeStamp now = mcc->Time();
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 2), now);
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 25), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, manager, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 25), mcc->Time());
+
+  // The velocity should be positive when panning with positive displacement.
+  EXPECT_GT(apzc->GetVelocityVector().y, 3.0);
+
+  mcc->AdvanceByMillis(5);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 80),
+             ScreenPoint(0, 0), mcc->Time());
+
+  // After lifting the fingers, the velocity should be zero and a smooth
+  // animation should have been triggered for scroll snap.
+  EXPECT_EQ(apzc->GetVelocityVector().y, 0);
+  apzc->AssertStateIsSmoothMsdScroll();
+
+  mcc->AdvanceByMillis(5);
+
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, manager,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 200), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, manager,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 50), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  apzc->AdvanceAnimations(mcc->GetSampleTime());
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, manager,
+             ScreenIntPoint(50, 80), ScreenPoint(0, 0), mcc->Time());
+
+  apzc->AdvanceAnimationsUntilEnd();
+  EXPECT_EQ(
+      100.0f,
+      apzc->GetCurrentAsyncScrollOffset(
+              AsyncPanZoomController::AsyncTransformConsumer::eForHitTesting)
+          .y);
+}
diff --git a/gfx/layers/apz/test/gtest/TestTransformNotifications.cpp b/gfx/layers/apz/test/gtest/TestTransformNotifications.cpp
new file mode 100644
index 0000000000..c3f53105fa
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestTransformNotifications.cpp
@@ -0,0 +1,461 @@
+/* -*- 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 "APZCBasicTester.h"
+#include "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "mozilla/layers/WebRenderScrollDataWrapper.h"
+
+#include "InputUtils.h"
+
+class APZCTransformNotificationTester : public APZCTreeManagerTester {
+ public:
+  explicit APZCTransformNotificationTester() { CreateMockHitTester(); }
+
+  UniquePtr<ScopedLayerTreeRegistration> mRegistration;
+
+  RefPtr<TestAsyncPanZoomController> mRootApzc;
+
+  void SetupBasicTest() {
+    const char* treeShape = "x";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 100, 100),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(root, ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 500, 500));
+
+    mRegistration = MakeUnique<ScopedLayerTreeRegistration>(LayersId{0}, mcc);
+
+    UpdateHitTestingTree();
+
+    mRootApzc = ApzcOf(root);
+  }
+};
+
+TEST_F(APZCTransformNotificationTester, PanningTransformNotifications) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  SetupBasicTest();
+
+  // Scroll down by 25 px. Ensure we only get one set of
+  // state change notifications.
+  //
+  // Then, scroll back up by 20px, this time flinging after.
+  // The fling should cover the remaining 5 px of room to scroll, then
+  // go into overscroll, and finally snap-back to recover from overscroll.
+  // Again, ensure we only get one set of state change notifications for
+  // this entire procedure.
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("Simple pan"));
+    EXPECT_CALL(*mcc,
+                NotifyAPZStateChange(
+                    _, GeckoContentController::APZStateChange::eStartTouch, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eStartPanning, _))
+        .Times(1);
+    EXPECT_CALL(*mcc,
+                NotifyAPZStateChange(
+                    _, GeckoContentController::APZStateChange::eEndTouch, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Complex pan"));
+    EXPECT_CALL(*mcc,
+                NotifyAPZStateChange(
+                    _, GeckoContentController::APZStateChange::eStartTouch, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eStartPanning, _))
+        .Times(1);
+    EXPECT_CALL(*mcc,
+                NotifyAPZStateChange(
+                    _, GeckoContentController::APZStateChange::eEndTouch, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Done"));
+  }
+
+  check.Call("Simple pan");
+  Pan(mRootApzc, 50, 25, PanOptions::NoFling);
+  check.Call("Complex pan");
+  Pan(mRootApzc, 25, 45);
+  mRootApzc->AdvanceAnimationsUntilEnd();
+  check.Call("Done");
+}
+
+TEST_F(APZCTransformNotificationTester, PanWithMomentumTransformNotifications) {
+  SetupBasicTest();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("Pan Start"));
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Panning"));
+    EXPECT_CALL(check, Call("Pan End"));
+    EXPECT_CALL(check, Call("Momentum Start"));
+
+    EXPECT_CALL(check, Call("Momentum Pan"));
+    EXPECT_CALL(check, Call("Momentum End"));
+    // The TransformEnd should only be sent after the momentum pan.
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Done"));
+  }
+
+  check.Call("Pan Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Panning");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, mRootApzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Pan End");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Momentum Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMSTART, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(30, 90), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Momentum Pan");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMPAN, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(10, 30), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Momentum End");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_MOMENTUMEND, manager,
+             ScreenIntPoint(50, 50), ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(10);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Done");
+}
+
+TEST_F(APZCTransformNotificationTester,
+       PanWithoutMomentumTransformNotifications) {
+  // Ensure that the TransformEnd delay is 100ms.
+  SCOPED_GFX_PREF_INT("apz.scrollend-event.content.delay_ms", 100);
+
+  SetupBasicTest();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("Pan Start"));
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Panning"));
+    EXPECT_CALL(check, Call("Pan End"));
+    EXPECT_CALL(check, Call("TransformEnd delay"));
+    // The TransformEnd should only be sent after the pan gesture and 100ms
+    // timer fire.
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Done"));
+  }
+
+  check.Call("Pan Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Panning");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, mRootApzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Pan End");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(55);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("TransformEnd delay");
+  mcc->AdvanceByMillis(55);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Done");
+}
+
+TEST_F(APZCTransformNotificationTester,
+       PanFollowedByNewPanTransformNotifications) {
+  // Ensure that the TransformEnd delay is 100ms.
+  SCOPED_GFX_PREF_INT("apz.scrollend-event.content.delay_ms", 100);
+
+  SetupBasicTest();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("Pan Start"));
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Panning"));
+    EXPECT_CALL(check, Call("Pan End"));
+    // The TransformEnd delay should be cut short and delivered before the
+    // new pan gesture begins.
+    EXPECT_CALL(check, Call("New Pan Start"));
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+    EXPECT_CALL(check, Call("New Pan End"));
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Done"));
+  }
+
+  check.Call("Pan Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Panning");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, mRootApzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Pan End");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(55);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("New Pan Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, mRootApzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("New Pan End");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(105);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Done");
+}
+
+TEST_F(APZCTransformNotificationTester,
+       PanFollowedByWheelTransformNotifications) {
+  // Ensure that the TransformEnd delay is 100ms.
+  SCOPED_GFX_PREF_INT("apz.scrollend-event.content.delay_ms", 100);
+
+  SetupBasicTest();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("Pan Start"));
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Panning"));
+    EXPECT_CALL(check, Call("Pan End"));
+    // The TransformEnd delay should be cut short and delivered before the
+    // new wheel event begins.
+    EXPECT_CALL(check, Call("Wheel Start"));
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Wheel End"));
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Done"));
+  }
+
+  check.Call("Pan Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Panning");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, mRootApzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, 30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Pan End");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(55);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Wheel Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  SmoothWheel(manager, ScreenIntPoint(50, 50), ScreenPoint(10, 10),
+              mcc->Time());
+  mcc->AdvanceByMillis(10);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Wheel End");
+
+  mRootApzc->AdvanceAnimationsUntilEnd();
+
+  check.Call("Done");
+}
+
+#ifndef MOZ_WIDGET_ANDROID  // Currently fails on Android
+TEST_F(APZCTransformNotificationTester, PanOverscrollTransformNotifications) {
+  SCOPED_GFX_PREF_BOOL("apz.overscroll.enabled", true);
+
+  SetupBasicTest();
+
+  MockFunction<void(std::string checkPointName)> check;
+  {
+    InSequence s;
+    EXPECT_CALL(check, Call("Pan Start"));
+    EXPECT_CALL(
+        *mcc,
+        NotifyAPZStateChange(
+            _, GeckoContentController::APZStateChange::eTransformBegin, _))
+        .Times(1);
+
+    EXPECT_CALL(check, Call("Panning Into Overscroll"));
+    EXPECT_CALL(check, Call("Pan End"));
+    EXPECT_CALL(check, Call("Overscroll Animation End"));
+    // The TransformEnd should only be sent after the overscroll animation
+    // completes.
+    EXPECT_CALL(
+        *mcc, NotifyAPZStateChange(
+                  _, GeckoContentController::APZStateChange::eTransformEnd, _))
+        .Times(1);
+    EXPECT_CALL(check, Call("Done"));
+  }
+
+  check.Call("Pan Start");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_START, manager, ScreenIntPoint(50, 50),
+             ScreenIntPoint(1, 2), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  check.Call("Panning Into Overscroll");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_PAN, mRootApzc, ScreenIntPoint(50, 50),
+             ScreenPoint(15, -30), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Ensure that we have overscrolled.
+  EXPECT_TRUE(mRootApzc->IsOverscrolled());
+
+  check.Call("Pan End");
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID);
+  PanGesture(PanGestureInput::PANGESTURE_END, manager, ScreenIntPoint(50, 50),
+             ScreenPoint(0, 0), mcc->Time());
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimations(mcc->GetSampleTime());
+
+  // Wait for the overscroll animation to complete and the TransformEnd
+  // notification to be sent.
+  check.Call("Overscroll Animation End");
+  mcc->AdvanceByMillis(5);
+  mRootApzc->AdvanceAnimationsUntilEnd();
+  EXPECT_FALSE(mRootApzc->IsOverscrolled());
+
+  check.Call("Done");
+}
+#endif
diff --git a/gfx/layers/apz/test/gtest/TestTreeManager.cpp b/gfx/layers/apz/test/gtest/TestTreeManager.cpp
new file mode 100644
index 0000000000..963a400cb8
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestTreeManager.cpp
@@ -0,0 +1,347 @@
+/* -*- 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 "APZCTreeManagerTester.h"
+#include "APZTestCommon.h"
+#include "InputUtils.h"
+#include "Units.h"
+
+class APZCTreeManagerGenericTester : public APZCTreeManagerTester {
+ protected:
+  void CreateSimpleScrollingLayer() {
+    const char* treeShape = "x";
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 200, 200),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(layers[0], ScrollableLayerGuid::START_SCROLL_ID,
+                              CSSRect(0, 0, 500, 500));
+  }
+
+  void CreateSimpleMultiLayerTree() {
+    const char* treeShape = "x(xx)";
+    // LayerID               0 12
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 100, 100),
+        LayerIntRect(0, 0, 100, 50),
+        LayerIntRect(0, 50, 100, 50),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+  }
+
+  void CreatePotentiallyLeakingTree() {
+    const char* treeShape = "x(x(x(x))x(x(x)))";
+    // LayerID               0 1 2 3  4 5 6
+    CreateScrollData(treeShape);
+    SetScrollableFrameMetrics(layers[0], ScrollableLayerGuid::START_SCROLL_ID);
+    SetScrollableFrameMetrics(layers[2],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1);
+    SetScrollableFrameMetrics(layers[5],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1);
+    SetScrollableFrameMetrics(layers[3],
+                              ScrollableLayerGuid::START_SCROLL_ID + 2);
+    SetScrollableFrameMetrics(layers[6],
+                              ScrollableLayerGuid::START_SCROLL_ID + 3);
+  }
+
+  void CreateTwoLayerTree(int32_t aRootContentLayerIndex) {
+    const char* treeShape = "x(x)";
+    // LayerID               0 1
+    LayerIntRegion layerVisibleRegion[] = {
+        LayerIntRect(0, 0, 100, 100),
+        LayerIntRect(0, 0, 100, 100),
+    };
+    CreateScrollData(treeShape, layerVisibleRegion);
+    SetScrollableFrameMetrics(layers[0], ScrollableLayerGuid::START_SCROLL_ID);
+    SetScrollableFrameMetrics(layers[1],
+                              ScrollableLayerGuid::START_SCROLL_ID + 1);
+    SetScrollHandoff(layers[1], layers[0]);
+
+    // Make layers[aRootContentLayerIndex] the root content
+    ModifyFrameMetrics(layers[aRootContentLayerIndex],
+                       [](ScrollMetadata& sm, FrameMetrics& fm) {
+                         fm.SetIsRootContent(true);
+                       });
+  }
+};
+
+TEST_F(APZCTreeManagerGenericTester, ScrollablePaintedLayers) {
+  CreateSimpleMultiLayerTree();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+
+  // both layers have the same scrollId
+  SetScrollableFrameMetrics(layers[1], ScrollableLayerGuid::START_SCROLL_ID);
+  SetScrollableFrameMetrics(layers[2], ScrollableLayerGuid::START_SCROLL_ID);
+  UpdateHitTestingTree();
+
+  TestAsyncPanZoomController* nullAPZC = nullptr;
+  // so they should have the same APZC
+  EXPECT_FALSE(HasScrollableFrameMetrics(layers[0]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[1]));
+  EXPECT_NE(nullAPZC, ApzcOf(layers[2]));
+  EXPECT_EQ(ApzcOf(layers[1]), ApzcOf(layers[2]));
+}
+
+TEST_F(APZCTreeManagerGenericTester, Bug1068268) {
+  CreatePotentiallyLeakingTree();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+
+  UpdateHitTestingTree();
+  RefPtr<HitTestingTreeNode> root = manager->GetRootNode();
+  RefPtr<HitTestingTreeNode> node2 = root->GetFirstChild()->GetFirstChild();
+  RefPtr<HitTestingTreeNode> node5 = root->GetLastChild()->GetLastChild();
+
+  EXPECT_EQ(ApzcOf(layers[2]), node5->GetApzc());
+  EXPECT_EQ(ApzcOf(layers[2]), node2->GetApzc());
+  EXPECT_EQ(ApzcOf(layers[0]), ApzcOf(layers[2])->GetParent());
+  EXPECT_EQ(ApzcOf(layers[2]), ApzcOf(layers[5]));
+
+  EXPECT_EQ(node2->GetFirstChild(), node2->GetLastChild());
+  EXPECT_EQ(ApzcOf(layers[3]), node2->GetLastChild()->GetApzc());
+  EXPECT_EQ(node5->GetFirstChild(), node5->GetLastChild());
+  EXPECT_EQ(ApzcOf(layers[6]), node5->GetLastChild()->GetApzc());
+  EXPECT_EQ(ApzcOf(layers[2]), ApzcOf(layers[3])->GetParent());
+  EXPECT_EQ(ApzcOf(layers[5]), ApzcOf(layers[6])->GetParent());
+}
+
+class APZCTreeManagerGenericTesterMock : public APZCTreeManagerGenericTester {
+ public:
+  APZCTreeManagerGenericTesterMock() { CreateMockHitTester(); }
+};
+
+TEST_F(APZCTreeManagerGenericTesterMock, Bug1194876) {
+  // Create a layer tree with parent and child scrollable layers, with the
+  // child being the root content.
+  CreateTwoLayerTree(1);
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  uint64_t blockId;
+  nsTArray<ScrollableLayerGuid> targets;
+
+  // First touch goes down, APZCTM will hit layers[1] because it is on top of
+  // layers[0], but we tell it the real target APZC is layers[0].
+  MultiTouchInput mti;
+  mti = CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(
+      SingleTouchData(0, ScreenIntPoint(25, 50), ScreenSize(0, 0), 0, 0));
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  blockId = manager->ReceiveInputEvent(mti).mInputBlockId;
+  manager->ContentReceivedInputBlock(blockId, false);
+  targets.AppendElement(ApzcOf(layers[0])->GetGuid());
+  manager->SetTargetAPZC(blockId, targets);
+
+  // Around here, the above touch will get processed by ApzcOf(layers[0])
+
+  // Second touch goes down (first touch remains down), APZCTM will again hit
+  // layers[1]. Again we tell it both touches landed on layers[0], but because
+  // layers[1] is the RCD layer, it will end up being the multitouch target.
+  mti.mTouches.AppendElement(
+      SingleTouchData(1, ScreenIntPoint(75, 50), ScreenSize(0, 0), 0, 0));
+  // Each touch will get hit-tested, so queue two hit-test results.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  blockId = manager->ReceiveInputEvent(mti).mInputBlockId;
+  manager->ContentReceivedInputBlock(blockId, false);
+  targets.AppendElement(ApzcOf(layers[0])->GetGuid());
+  manager->SetTargetAPZC(blockId, targets);
+
+  // Around here, the above multi-touch will get processed by ApzcOf(layers[1]).
+  // We want to ensure that ApzcOf(layers[0]) has had its state cleared, because
+  // otherwise it will do things like dispatch spurious long-tap events.
+
+  EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap, _, _, _, _)).Times(0);
+}
+
+TEST_F(APZCTreeManagerGenericTesterMock, TargetChangesMidGesture_Bug1570559) {
+  // Create a layer tree with parent and child scrollable layers, with the
+  // parent being the root content.
+  CreateTwoLayerTree(0);
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  uint64_t blockId;
+  nsTArray<ScrollableLayerGuid> targets;
+
+  // First touch goes down. APZCTM hits the child layer because it is on top
+  // (and we confirm this target), but do not prevent-default the event, causing
+  // the child APZC's gesture detector to start a long-tap timeout task.
+  MultiTouchInput mti =
+      CreateMultiTouchInput(MultiTouchInput::MULTITOUCH_START, mcc->Time());
+  mti.mTouches.AppendElement(
+      SingleTouchData(0, ScreenIntPoint(25, 50), ScreenSize(0, 0), 0, 0));
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  blockId = manager->ReceiveInputEvent(mti).mInputBlockId;
+  manager->ContentReceivedInputBlock(blockId, /* default prevented = */ false);
+  targets.AppendElement(ApzcOf(layers[1])->GetGuid());
+  manager->SetTargetAPZC(blockId, targets);
+
+  // Second touch goes down (first touch remains down). APZCTM again hits the
+  // child and we confirm this, but multi-touch events are routed to the root
+  // content APZC which is the parent. This event is prevent-defaulted, so we
+  // clear the parent's gesture state. The bug is that we fail to clear the
+  // child's gesture state.
+  mti.mTouches.AppendElement(
+      SingleTouchData(1, ScreenIntPoint(75, 50), ScreenSize(0, 0), 0, 0));
+  // Each touch will get hit-tested, so queue two hit-test results.
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID + 1,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  blockId = manager->ReceiveInputEvent(mti).mInputBlockId;
+  manager->ContentReceivedInputBlock(blockId, /* default prevented = */ true);
+  targets.AppendElement(ApzcOf(layers[1])->GetGuid());
+  manager->SetTargetAPZC(blockId, targets);
+
+  // If we've failed to clear the child's gesture state, then the long tap
+  // timeout task will fire in TearDown() and a long-tap will be dispatched.
+  EXPECT_CALL(*mcc, HandleTap(TapType::eLongTap, _, _, _, _)).Times(0);
+}
+
+TEST_F(APZCTreeManagerGenericTesterMock, Bug1198900) {
+  // This is just a test that cancels a wheel event to make sure it doesn't
+  // crash.
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  ScreenPoint origin(100, 50);
+  ScrollWheelInput swi(mcc->Time(), 0, ScrollWheelInput::SCROLLMODE_INSTANT,
+                       ScrollWheelInput::SCROLLDELTA_PIXEL, origin, 0, 10,
+                       false, WheelDeltaAdjustmentStrategy::eNone);
+  uint64_t blockId;
+  QueueMockHitResult(ScrollableLayerGuid::START_SCROLL_ID,
+                     {CompositorHitTestFlags::eVisibleToHitTest,
+                      CompositorHitTestFlags::eIrregularArea});
+  blockId = manager->ReceiveInputEvent(swi).mInputBlockId;
+  manager->ContentReceivedInputBlock(blockId, /* preventDefault= */ true);
+}
+
+// The next two tests check that APZ clamps the scroll offset it composites even
+// if the main thread fails to do so. (The main thread will always clamp its
+// scroll offset internally, but it may not send APZ the clamped version for
+// scroll offset synchronization reasons.)
+TEST_F(APZCTreeManagerTester, Bug1551582) {
+  // The simple layer tree has a scrollable rect of 500x500 and a composition
+  // bounds of 200x200, leading to a scroll range of (0,0,300,300).
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  // Simulate the main thread scrolling to the end of the scroll range.
+  ModifyFrameMetrics(root, [](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    aMetrics.SetLayoutScrollOffset(CSSPoint(300, 300));
+    nsTArray<ScrollPositionUpdate> scrollUpdates;
+    scrollUpdates.AppendElement(ScrollPositionUpdate::NewScroll(
+        ScrollOrigin::Other, CSSPoint::ToAppUnits(CSSPoint(300, 300))));
+    aSm.SetScrollUpdates(scrollUpdates);
+    aMetrics.SetScrollGeneration(scrollUpdates.LastElement().GetGeneration());
+  });
+  UpdateHitTestingTree();
+
+  // Sanity check.
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+  CSSPoint compositedScrollOffset = apzc->GetCompositedScrollOffset();
+  EXPECT_EQ(CSSPoint(300, 300), compositedScrollOffset);
+
+  // Simulate the main thread shrinking the scrollable rect to 400x400 (and
+  // thereby the scroll range to (0,0,200,200) without sending a new scroll
+  // offset update for the clamped scroll position (200,200).
+  ModifyFrameMetrics(root, [](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    aMetrics.SetScrollableRect(CSSRect(0, 0, 400, 400));
+  });
+  UpdateHitTestingTree();
+
+  // Check that APZ has clamped the scroll offset to (200,200) for us.
+  compositedScrollOffset = apzc->GetCompositedScrollOffset();
+  EXPECT_EQ(CSSPoint(200, 200), compositedScrollOffset);
+}
+TEST_F(APZCTreeManagerTester, Bug1557424) {
+  // The simple layer tree has a scrollable rect of 500x500 and a composition
+  // bounds of 200x200, leading to a scroll range of (0,0,300,300).
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+
+  // Simulate the main thread scrolling to the end of the scroll range.
+  ModifyFrameMetrics(root, [](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    aMetrics.SetLayoutScrollOffset(CSSPoint(300, 300));
+    nsTArray<ScrollPositionUpdate> scrollUpdates;
+    scrollUpdates.AppendElement(ScrollPositionUpdate::NewScroll(
+        ScrollOrigin::Other, CSSPoint::ToAppUnits(CSSPoint(300, 300))));
+    aSm.SetScrollUpdates(scrollUpdates);
+    aMetrics.SetScrollGeneration(scrollUpdates.LastElement().GetGeneration());
+  });
+  UpdateHitTestingTree();
+
+  // Sanity check.
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+  CSSPoint compositedScrollOffset = apzc->GetCompositedScrollOffset();
+  EXPECT_EQ(CSSPoint(300, 300), compositedScrollOffset);
+
+  // Simulate the main thread expanding the composition bounds to 300x300 (and
+  // thereby shrinking the scroll range to (0,0,200,200) without sending a new
+  // scroll offset update for the clamped scroll position (200,200).
+  ModifyFrameMetrics(root, [](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    aMetrics.SetCompositionBounds(ParentLayerRect(0, 0, 300, 300));
+  });
+  UpdateHitTestingTree();
+
+  // Check that APZ has clamped the scroll offset to (200,200) for us.
+  compositedScrollOffset = apzc->GetCompositedScrollOffset();
+  EXPECT_EQ(CSSPoint(200, 200), compositedScrollOffset);
+}
+
+TEST_F(APZCTreeManagerTester, Bug1805601) {
+  // The simple layer tree has a scrollable rect of 500x500 and a composition
+  // bounds of 200x200, leading to a scroll range of (0,0,300,300) at unit zoom.
+  CreateSimpleScrollingLayer();
+  ScopedLayerTreeRegistration registration(LayersId{0}, mcc);
+  UpdateHitTestingTree();
+  RefPtr<TestAsyncPanZoomController> apzc = ApzcOf(root);
+  FrameMetrics& compositorMetrics = apzc->GetFrameMetrics();
+  EXPECT_EQ(CSSRect(0, 0, 300, 300), compositorMetrics.CalculateScrollRange());
+
+  // Zoom the page in by 2x. This needs to be reflected in each of the pres
+  // shell resolution, cumulative resolution, and zoom. This makes the scroll
+  // range (0,0,400,400).
+  compositorMetrics.SetZoom(CSSToParentLayerScale(2.0));
+  EXPECT_EQ(CSSRect(0, 0, 400, 400), compositorMetrics.CalculateScrollRange());
+
+  // Scroll to an area inside the 2x scroll range but outside the original one.
+  compositorMetrics.ClampAndSetVisualScrollOffset(CSSPoint(350, 350));
+  EXPECT_EQ(CSSPoint(350, 350), compositorMetrics.GetVisualScrollOffset());
+
+  // Simulate a main-thread update where the zoom is reset to 1x but the visual
+  // scroll offset is unmodified.
+  ModifyFrameMetrics(root, [](ScrollMetadata& aSm, FrameMetrics& aMetrics) {
+    // Changes to |compositorMetrics| are not reflected in |aMetrics|, which
+    // is the "layer tree" copy, so we don't need to explicitly set the zoom to
+    // 1.0 (it still has that as the initial value), but we do need to set
+    // the visual scroll offset to the same value the APZ copy has.
+    aMetrics.SetVisualScrollOffset(CSSPoint(350, 350));
+
+    // Needed to get APZ to accept the 1.0 zoom in |aMetrics|, otherwise
+    // it will act as though its zoom is newer (e.g. an async zoom that hasn't
+    // been repainted yet) and ignore ours.
+    aSm.SetResolutionUpdated(true);
+  });
+  UpdateHitTestingTree();
+
+  // Check that APZ clamped the scroll offset.
+  EXPECT_EQ(CSSRect(0, 0, 300, 300), compositorMetrics.CalculateScrollRange());
+  EXPECT_EQ(CSSPoint(300, 300), compositorMetrics.GetVisualScrollOffset());
+}
diff --git a/gfx/layers/apz/test/gtest/TestWRScrollData.cpp b/gfx/layers/apz/test/gtest/TestWRScrollData.cpp
new file mode 100644
index 0000000000..e267e58e90
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestWRScrollData.cpp
@@ -0,0 +1,273 @@
+/* -*- 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 "TestWRScrollData.h"
+#include "APZTestAccess.h"
+#include "gtest/gtest.h"
+#include "FrameMetrics.h"
+#include "gfxPlatform.h"
+#include "mozilla/layers/APZUpdater.h"
+#include "mozilla/layers/LayersTypes.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+#include "mozilla/layers/WebRenderScrollDataWrapper.h"
+#include "mozilla/UniquePtr.h"
+#include "apz/src/APZCTreeManager.h"
+
+using mozilla::layers::APZCTreeManager;
+using mozilla::layers::APZUpdater;
+using mozilla::layers::LayersId;
+using mozilla::layers::ScrollableLayerGuid;
+using mozilla::layers::ScrollMetadata;
+using mozilla::layers::TestWRScrollData;
+using mozilla::layers::WebRenderLayerScrollData;
+using mozilla::layers::WebRenderScrollDataWrapper;
+
+/* static */
+TestWRScrollData TestWRScrollData::Create(const char* aTreeShape,
+                                          const APZUpdater& aUpdater,
+                                          const LayerIntRegion* aVisibleRegions,
+                                          const gfx::Matrix4x4* aTransforms) {
+  // The WebRenderLayerScrollData tree needs to be created in a fairly
+  // particular way (for example, each node needs to know the number of
+  // descendants it has), so this function takes care to create the nodes
+  // in the same order as WebRenderCommandBuilder would.
+  TestWRScrollData result;
+  const size_t len = strlen(aTreeShape);
+  // "Layer index" in this function refers to the index by which a layer will
+  // be accessible via TestWRScrollData::GetLayer(), and matches the order
+  // in which the layer appears in |aTreeShape|.
+  size_t currentLayerIndex = 0;
+  struct LayerEntry {
+    size_t mLayerIndex;
+    int32_t mDescendantCount = 0;
+  };
+  // Layers we have encountered in |aTreeShape|, but have not built a
+  // WebRenderLayerScrollData for. (It can only be built after its
+  // descendants have been encountered and counted.)
+  std::stack<LayerEntry> pendingLayers;
+  std::vector<WebRenderLayerScrollData> finishedLayers;
+  // Tracks the level of nesting of '(' characters. Starts at 1 to account
+  // for the root layer.
+  size_t depth = 1;
+  // Helper function for finishing a layer once all its descendants have been
+  // encountered.
+  auto finishLayer = [&] {
+    MOZ_ASSERT(!pendingLayers.empty());
+    LayerEntry entry = pendingLayers.top();
+
+    WebRenderLayerScrollData layer;
+    APZTestAccess::InitializeForTest(layer, entry.mDescendantCount);
+    if (aVisibleRegions) {
+      layer.SetVisibleRegion(aVisibleRegions[entry.mLayerIndex]);
+    }
+    if (aTransforms) {
+      layer.SetTransform(aTransforms[entry.mLayerIndex]);
+    }
+    finishedLayers.push_back(std::move(layer));
+
+    // |finishedLayers| stores the layers in a different order than they
+    // appeared in |aTreeShape|. To be able to access layers by their layer
+    // index, keep a mapping from layer index to index in |finishedLayers|.
+    result.mIndexMap.emplace(entry.mLayerIndex, finishedLayers.size() - 1);
+
+    pendingLayers.pop();
+
+    // Keep track of descendant counts. The +1 is for the layer just finished.
+    if (!pendingLayers.empty()) {
+      pendingLayers.top().mDescendantCount += (entry.mDescendantCount + 1);
+    }
+  };
+  for (size_t i = 0; i < len; ++i) {
+    if (aTreeShape[i] == '(') {
+      ++depth;
+    } else if (aTreeShape[i] == ')') {
+      if (pendingLayers.size() <= 1) {
+        printf("Invalid tree shape: too many ')'\n");
+        MOZ_CRASH();
+      }
+      finishLayer();  // finish last layer at current depth
+      --depth;
+    } else {
+      if (aTreeShape[i] != 'x') {
+        printf("The only allowed character to represent a layer is 'x'\n");
+        MOZ_CRASH();
+      }
+      if (depth == pendingLayers.size()) {
+        // We have a previous layer at this same depth to finish.
+        if (depth <= 1) {
+          printf("The tree is only allowed to have one root\n");
+          MOZ_CRASH();
+        }
+        finishLayer();
+      }
+      MOZ_ASSERT(depth == pendingLayers.size() + 1);
+      pendingLayers.push({currentLayerIndex});
+      ++currentLayerIndex;
+    }
+  }
+  if (pendingLayers.size() != 1) {
+    printf("Invalid tree shape: '(' and ')' not balanced\n");
+    MOZ_CRASH();
+  }
+  finishLayer();  // finish root layer
+
+  // As in WebRenderCommandBuilder, the layers need to be added to the
+  // WebRenderScrollData in reverse of the order in which they were built.
+  for (auto it = finishedLayers.rbegin(); it != finishedLayers.rend(); ++it) {
+    result.AddLayerData(std::move(*it));
+  }
+  // mIndexMap also needs to be adjusted to accout for the reversal above.
+  for (auto& [layerIndex, storedIndex] : result.mIndexMap) {
+    (void)layerIndex;  // suppress -Werror=unused-variable
+    storedIndex = result.GetLayerCount() - storedIndex - 1;
+  }
+
+  return result;
+}
+
+const WebRenderLayerScrollData* TestWRScrollData::operator[](
+    size_t aLayerIndex) const {
+  auto it = mIndexMap.find(aLayerIndex);
+  if (it == mIndexMap.end()) {
+    return nullptr;
+  }
+  return GetLayerData(it->second);
+}
+
+WebRenderLayerScrollData* TestWRScrollData::operator[](size_t aLayerIndex) {
+  auto it = mIndexMap.find(aLayerIndex);
+  if (it == mIndexMap.end()) {
+    return nullptr;
+  }
+  return GetLayerData(it->second);
+}
+
+void TestWRScrollData::SetScrollMetadata(
+    size_t aLayerIndex, const nsTArray<ScrollMetadata>& aMetadata) {
+  WebRenderLayerScrollData* layer = operator[](aLayerIndex);
+  MOZ_ASSERT(layer);
+  for (const ScrollMetadata& metadata : aMetadata) {
+    layer->AppendScrollMetadata(*this, metadata);
+  }
+}
+
+class WebRenderScrollDataWrapperTester : public ::testing::Test {
+ protected:
+  virtual void SetUp() {
+    // This ensures ScrollMetadata::sNullMetadata is initialized.
+    gfxPlatform::GetPlatform();
+
+    mManager = new APZCTreeManager(LayersId{0});
+    mUpdater = new APZUpdater(mManager, false);
+  }
+
+  RefPtr<APZCTreeManager> mManager;
+  RefPtr<APZUpdater> mUpdater;
+};
+
+TEST_F(WebRenderScrollDataWrapperTester, SimpleTree) {
+  auto layers = TestWRScrollData::Create("x(x(x(xx)x(x)))", *mUpdater);
+  WebRenderScrollDataWrapper w0(*mUpdater, &layers);
+
+  ASSERT_EQ(layers[0], w0.GetLayer());
+  WebRenderScrollDataWrapper w1 = w0.GetLastChild();
+  ASSERT_EQ(layers[1], w1.GetLayer());
+  ASSERT_FALSE(w1.GetPrevSibling().IsValid());
+  WebRenderScrollDataWrapper w5 = w1.GetLastChild();
+  ASSERT_EQ(layers[5], w5.GetLayer());
+  WebRenderScrollDataWrapper w6 = w5.GetLastChild();
+  ASSERT_EQ(layers[6], w6.GetLayer());
+  ASSERT_FALSE(w6.GetLastChild().IsValid());
+  WebRenderScrollDataWrapper w2 = w5.GetPrevSibling();
+  ASSERT_EQ(layers[2], w2.GetLayer());
+  ASSERT_FALSE(w2.GetPrevSibling().IsValid());
+  WebRenderScrollDataWrapper w4 = w2.GetLastChild();
+  ASSERT_EQ(layers[4], w4.GetLayer());
+  ASSERT_FALSE(w4.GetLastChild().IsValid());
+  WebRenderScrollDataWrapper w3 = w4.GetPrevSibling();
+  ASSERT_EQ(layers[3], w3.GetLayer());
+  ASSERT_FALSE(w3.GetLastChild().IsValid());
+  ASSERT_FALSE(w3.GetPrevSibling().IsValid());
+}
+
+static ScrollMetadata MakeMetadata(ScrollableLayerGuid::ViewID aId) {
+  ScrollMetadata metadata;
+  metadata.GetMetrics().SetScrollId(aId);
+  return metadata;
+}
+
+TEST_F(WebRenderScrollDataWrapperTester, MultiFramemetricsTree) {
+  auto layers = TestWRScrollData::Create("x(x(x(xx)x(x)))", *mUpdater);
+
+  nsTArray<ScrollMetadata> metadata;
+  metadata.InsertElementAt(0,
+                           MakeMetadata(ScrollableLayerGuid::START_SCROLL_ID +
+                                        0));  // topmost of root layer
+  metadata.InsertElementAt(0,
+                           MakeMetadata(ScrollableLayerGuid::NULL_SCROLL_ID));
+  metadata.InsertElementAt(
+      0, MakeMetadata(ScrollableLayerGuid::START_SCROLL_ID + 1));
+  metadata.InsertElementAt(
+      0, MakeMetadata(ScrollableLayerGuid::START_SCROLL_ID + 2));
+  metadata.InsertElementAt(0,
+                           MakeMetadata(ScrollableLayerGuid::NULL_SCROLL_ID));
+  metadata.InsertElementAt(
+      0, MakeMetadata(
+             ScrollableLayerGuid::NULL_SCROLL_ID));  // bottom of root layer
+  layers.SetScrollMetadata(0, metadata);
+
+  metadata.Clear();
+  metadata.InsertElementAt(
+      0, MakeMetadata(ScrollableLayerGuid::START_SCROLL_ID + 3));
+  layers.SetScrollMetadata(1, metadata);
+
+  metadata.Clear();
+  metadata.InsertElementAt(
+      0, MakeMetadata(ScrollableLayerGuid::START_SCROLL_ID + 4));
+  layers.SetScrollMetadata(2, metadata);
+
+  metadata.Clear();
+  metadata.InsertElementAt(
+      0, MakeMetadata(ScrollableLayerGuid::START_SCROLL_ID + 5));
+  layers.SetScrollMetadata(4, metadata);
+
+  metadata.Clear();
+  metadata.InsertElementAt(0,
+                           MakeMetadata(ScrollableLayerGuid::NULL_SCROLL_ID));
+  metadata.InsertElementAt(
+      0, MakeMetadata(ScrollableLayerGuid::START_SCROLL_ID + 6));
+  layers.SetScrollMetadata(5, metadata);
+
+  WebRenderScrollDataWrapper wrapper(*mUpdater, &layers);
+  nsTArray<WebRenderLayerScrollData*> expectedLayers;
+  expectedLayers.AppendElement(layers[0]);
+  expectedLayers.AppendElement(layers[0]);
+  expectedLayers.AppendElement(layers[0]);
+  expectedLayers.AppendElement(layers[0]);
+  expectedLayers.AppendElement(layers[0]);
+  expectedLayers.AppendElement(layers[0]);
+  expectedLayers.AppendElement(layers[1]);
+  expectedLayers.AppendElement(layers[5]);
+  expectedLayers.AppendElement(layers[5]);
+  expectedLayers.AppendElement(layers[6]);
+  nsTArray<ScrollableLayerGuid::ViewID> expectedIds;
+  expectedIds.AppendElement(ScrollableLayerGuid::START_SCROLL_ID + 0);
+  expectedIds.AppendElement(ScrollableLayerGuid::NULL_SCROLL_ID);
+  expectedIds.AppendElement(ScrollableLayerGuid::START_SCROLL_ID + 1);
+  expectedIds.AppendElement(ScrollableLayerGuid::START_SCROLL_ID + 2);
+  expectedIds.AppendElement(ScrollableLayerGuid::NULL_SCROLL_ID);
+  expectedIds.AppendElement(ScrollableLayerGuid::NULL_SCROLL_ID);
+  expectedIds.AppendElement(ScrollableLayerGuid::START_SCROLL_ID + 3);
+  expectedIds.AppendElement(ScrollableLayerGuid::NULL_SCROLL_ID);
+  expectedIds.AppendElement(ScrollableLayerGuid::START_SCROLL_ID + 6);
+  expectedIds.AppendElement(ScrollableLayerGuid::NULL_SCROLL_ID);
+  for (int i = 0; i < 10; i++) {
+    ASSERT_EQ(expectedLayers[i], wrapper.GetLayer());
+    ASSERT_EQ(expectedIds[i], wrapper.Metrics().GetScrollId());
+    wrapper = wrapper.GetLastChild();
+  }
+  ASSERT_FALSE(wrapper.IsValid());
+}
diff --git a/gfx/layers/apz/test/gtest/TestWRScrollData.h b/gfx/layers/apz/test/gtest/TestWRScrollData.h
new file mode 100644
index 0000000000..92e79aaee0
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/TestWRScrollData.h
@@ -0,0 +1,63 @@
+/* -*- 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_TestWRScrollData_h
+#define mozilla_layers_TestWRScrollData_h
+
+#include "mozilla/gfx/MatrixFwd.h"
+#include "mozilla/layers/WebRenderScrollData.h"
+
+namespace mozilla {
+namespace layers {
+
+class APZUpdater;
+
+// Extends WebRenderScrollData with some methods useful for gtests.
+class TestWRScrollData : public WebRenderScrollData {
+ public:
+  TestWRScrollData() = default;
+  TestWRScrollData(TestWRScrollData&& aOther) = default;
+  TestWRScrollData& operator=(TestWRScrollData&& aOther) = default;
+
+  /*
+   * Create a WebRenderLayerScrollData tree described by |aTreeShape|.
+   * |aTreeShape| is expected to be a string where each character is
+   * either 'x' to indicate a node in the tree, or a '(' or ')' to indicate
+   * the start/end of a subtree.
+   *
+   * Example "x(x(x(xx)x))" would yield:
+   *          x
+   *          |
+   *          x
+   *         / \
+   *        x   x
+   *       / \
+   *      x   x
+   *
+   * The caller may optionally provide visible regions and/or transforms
+   * for the nodes. If provided, the array should contain one element
+   * for each node, in the same order as in |aTreeShape|.
+   */
+  static TestWRScrollData Create(
+      const char* aTreeShape, const APZUpdater& aUpdater,
+      const LayerIntRegion* aVisibleRegions = nullptr,
+      const gfx::Matrix4x4* aTransforms = nullptr);
+
+  // These methods allow accessing and manipulating layers based on an index
+  // representing the order in which they appear in |aTreeShape|.
+  WebRenderLayerScrollData* operator[](size_t aLayerIndex);
+  const WebRenderLayerScrollData* operator[](size_t aLayerIndex) const;
+  void SetScrollMetadata(size_t aLayerIndex,
+                         const nsTArray<ScrollMetadata>& aMetadata);
+
+ private:
+  std::map<size_t, size_t> mIndexMap;  // Used to implement GetLayer()
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif
diff --git a/gfx/layers/apz/test/gtest/moz.build b/gfx/layers/apz/test/gtest/moz.build
new file mode 100644
index 0000000000..c7ec2e5f0b
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/moz.build
@@ -0,0 +1,38 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+UNIFIED_SOURCES += [
+    "APZTestAccess.cpp",
+    "APZTestCommon.cpp",
+    "MockHitTester.cpp",
+    "TestAxisLock.cpp",
+    "TestBasic.cpp",
+    "TestEventRegions.cpp",
+    "TestEventResult.cpp",
+    "TestFlingAcceleration.cpp",
+    "TestGestureDetector.cpp",
+    "TestHitTesting.cpp",
+    "TestInputQueue.cpp",
+    "TestOverscroll.cpp",
+    "TestPanning.cpp",
+    "TestPinching.cpp",
+    "TestScrollHandoff.cpp",
+    "TestSnapping.cpp",
+    "TestSnappingOnMomentum.cpp",
+    "TestTransformNotifications.cpp",
+    "TestTreeManager.cpp",
+    "TestWRScrollData.cpp",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+LOCAL_INCLUDES += [
+    "/gfx/2d",
+    "/gfx/cairo/cairo/src",
+    "/gfx/layers",
+]
+
+FINAL_LIBRARY = "xul-gtest"
diff --git a/gfx/layers/apz/test/gtest/mvm/TestMobileViewportManager.cpp b/gfx/layers/apz/test/gtest/mvm/TestMobileViewportManager.cpp
new file mode 100644
index 0000000000..cd7e0a7d0d
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/mvm/TestMobileViewportManager.cpp
@@ -0,0 +1,220 @@
+/* -*- 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 "gtest/gtest.h"
+#include "gmock/gmock.h"
+
+#include <functional>
+
+#include "MobileViewportManager.h"
+#include "mozilla/MVMContext.h"
+#include "mozilla/dom/Event.h"
+
+using namespace mozilla;
+
+class MockMVMContext : public MVMContext {
+  using AutoSizeFlag = nsViewportInfo::AutoSizeFlag;
+  using AutoScaleFlag = nsViewportInfo::AutoScaleFlag;
+  using ZoomFlag = nsViewportInfo::ZoomFlag;
+
+  // A "layout function" is a function that computes the content size
+  // as a function of the ICB size.
+  using LayoutFunction = std::function<CSSSize(CSSSize aICBSize)>;
+
+ public:
+  // MVMContext methods we don't care to implement.
+  MOCK_METHOD3(AddEventListener,
+               void(const nsAString& aType, nsIDOMEventListener* aListener,
+                    bool aUseCapture));
+  MOCK_METHOD3(RemoveEventListener,
+               void(const nsAString& aType, nsIDOMEventListener* aListener,
+                    bool aUseCapture));
+  MOCK_METHOD3(AddObserver, void(nsIObserver* aObserver, const char* aTopic,
+                                 bool aOwnsWeak));
+  MOCK_METHOD2(RemoveObserver,
+               void(nsIObserver* aObserver, const char* aTopic));
+  MOCK_METHOD0(Destroy, void());
+
+  MOCK_METHOD1(SetVisualViewportSize, void(const CSSSize& aSize));
+  MOCK_METHOD0(PostVisualViewportResizeEventByDynamicToolbar, void());
+  MOCK_METHOD0(UpdateDisplayPortMargins, void());
+
+  void SetMVM(MobileViewportManager* aMVM) { mMVM = aMVM; }
+
+  // MVMContext method implementations.
+  nsViewportInfo GetViewportInfo(const ScreenIntSize& aDisplaySize) const {
+    // This is a very basic approximation of what Document::GetViewportInfo()
+    // does in the most common cases.
+    // Ideally, we would invoke the algorithm in Document::GetViewportInfo()
+    // itself, but that would require refactoring it a bit to remove
+    // dependencies on the actual Document which we don't have available in
+    // this test harness.
+    CSSSize viewportSize = mDisplaySize / mDeviceScale;
+    if (mAutoSizeFlag == AutoSizeFlag::FixedSize) {
+      viewportSize = CSSSize(mFixedViewportWidth,
+                             mFixedViewportWidth * (float(mDisplaySize.height) /
+                                                    mDisplaySize.width));
+    }
+    return nsViewportInfo(mDefaultScale, mMinScale, mMaxScale, viewportSize,
+                          mAutoSizeFlag, mAutoScaleFlag, mZoomFlag,
+                          dom::ViewportFitType::Auto);
+  }
+  CSSToLayoutDeviceScale CSSToDevPixelScale() const { return mDeviceScale; }
+  float GetResolution() const { return mResolution; }
+  bool SubjectMatchesDocument(nsISupports* aSubject) const { return true; }
+  Maybe<CSSRect> CalculateScrollableRectForRSF() const {
+    return Some(CSSRect(CSSPoint(), mContentSize));
+  }
+  bool IsResolutionUpdatedByApz() const { return false; }
+  LayoutDeviceMargin ScrollbarAreaToExcludeFromCompositionBounds() const {
+    return LayoutDeviceMargin();
+  }
+  Maybe<LayoutDeviceIntSize> GetContentViewerSize() const {
+    return Some(mDisplaySize);
+  }
+  bool AllowZoomingForDocument() const { return true; }
+  bool IsInReaderMode() const { return false; }
+  bool IsDocumentLoading() const { return false; }
+
+  void SetResolutionAndScaleTo(float aResolution,
+                               ResolutionChangeOrigin aOrigin) {
+    mResolution = aResolution;
+    mMVM->ResolutionUpdated(aOrigin);
+  }
+  void Reflow(const CSSSize& aNewSize) {
+    mICBSize = aNewSize;
+    mContentSize = mLayoutFunction(mICBSize);
+  }
+
+  // Allow test code to modify the input metrics.
+  void SetMinScale(CSSToScreenScale aMinScale) { mMinScale = aMinScale; }
+  void SetMaxScale(CSSToScreenScale aMaxScale) { mMaxScale = aMaxScale; }
+  void SetInitialScale(CSSToScreenScale aInitialScale) {
+    mDefaultScale = aInitialScale;
+    mAutoScaleFlag = AutoScaleFlag::FixedScale;
+  }
+  void SetFixedViewportWidth(CSSCoord aWidth) {
+    mFixedViewportWidth = aWidth;
+    mAutoSizeFlag = AutoSizeFlag::FixedSize;
+  }
+  void SetDisplaySize(const LayoutDeviceIntSize& aNewDisplaySize) {
+    mDisplaySize = aNewDisplaySize;
+  }
+  void SetLayoutFunction(const LayoutFunction& aLayoutFunction) {
+    mLayoutFunction = aLayoutFunction;
+  }
+
+  // Allow test code to query the output metrics.
+  CSSSize GetICBSize() const { return mICBSize; }
+  CSSSize GetContentSize() const { return mContentSize; }
+
+ private:
+  // Input metrics, with some sensible defaults.
+  LayoutDeviceIntSize mDisplaySize{300, 600};
+  CSSToScreenScale mDefaultScale{1.0f};
+  CSSToScreenScale mMinScale{0.25f};
+  CSSToScreenScale mMaxScale{10.0f};
+  CSSToLayoutDeviceScale mDeviceScale{1.0f};
+  CSSCoord mFixedViewportWidth;
+  AutoSizeFlag mAutoSizeFlag = AutoSizeFlag::AutoSize;
+  AutoScaleFlag mAutoScaleFlag = AutoScaleFlag::AutoScale;
+  ZoomFlag mZoomFlag = ZoomFlag::AllowZoom;
+  // As a default layout function, just set the content size to the ICB size.
+  LayoutFunction mLayoutFunction = [](CSSSize aICBSize) { return aICBSize; };
+
+  // Output metrics.
+  float mResolution = 1.0f;
+  CSSSize mICBSize;
+  CSSSize mContentSize;
+
+  MobileViewportManager* mMVM = nullptr;
+};
+
+class MVMTester : public ::testing::Test {
+ public:
+  MVMTester()
+      : mMVMContext(new MockMVMContext()),
+        mMVM(new MobileViewportManager(
+            mMVMContext,
+            MobileViewportManager::ManagerType::VisualAndMetaViewport)) {
+    mMVMContext->SetMVM(mMVM.get());
+  }
+
+  void Resize(const LayoutDeviceIntSize& aNewDisplaySize) {
+    mMVMContext->SetDisplaySize(aNewDisplaySize);
+    mMVM->RequestReflow(false);
+  }
+
+ protected:
+  RefPtr<MockMVMContext> mMVMContext;
+  RefPtr<MobileViewportManager> mMVM;
+};
+
+TEST_F(MVMTester, ZoomBoundsRespectedAfterRotation_Bug1536755) {
+  // Set up initial conditions.
+  mMVMContext->SetDisplaySize(LayoutDeviceIntSize(600, 300));
+  mMVMContext->SetInitialScale(CSSToScreenScale(1.0f));
+  mMVMContext->SetMinScale(CSSToScreenScale(1.0f));
+  mMVMContext->SetMaxScale(CSSToScreenScale(1.0f));
+  // Set a layout function that simulates a page which is twice
+  // as tall as it is wide.
+  mMVMContext->SetLayoutFunction([](CSSSize aICBSize) {
+    return CSSSize(aICBSize.width, aICBSize.width * 2);
+  });
+
+  // Perform an initial viewport computation and reflow, and
+  // sanity-check the results.
+  mMVM->SetInitialViewport();
+  EXPECT_EQ(CSSSize(600, 300), mMVMContext->GetICBSize());
+  EXPECT_EQ(CSSSize(600, 1200), mMVMContext->GetContentSize());
+  EXPECT_EQ(1.0f, mMVMContext->GetResolution());
+
+  // Now rotate the screen, and check that the minimum and maximum
+  // scales are still respected after the rotation.
+  Resize(LayoutDeviceIntSize(300, 600));
+  EXPECT_EQ(CSSSize(300, 600), mMVMContext->GetICBSize());
+  EXPECT_EQ(CSSSize(300, 600), mMVMContext->GetContentSize());
+  EXPECT_EQ(1.0f, mMVMContext->GetResolution());
+}
+
+TEST_F(MVMTester, LandscapeToPortraitRotation_Bug1523844) {
+  // Set up initial conditions.
+  mMVMContext->SetDisplaySize(LayoutDeviceIntSize(300, 600));
+  // Set a layout function that simulates a page with a fixed
+  // content size that's as wide as the screen in one orientation
+  // (and wider in the other).
+  mMVMContext->SetLayoutFunction(
+      [](CSSSize aICBSize) { return CSSSize(600, 1200); });
+
+  // Simulate a "DOMMetaAdded" event being fired before calling
+  // SetInitialViewport(). This matches what typically happens
+  // during real usage (the MVM receives the "DOMMetaAdded"
+  // before the "load", and it's the "load" that calls
+  // SetInitialViewport()), and is important to trigger this
+  // bug, because it causes the MVM to be stuck with an
+  // "mRestoreResolution" (prior to the fix).
+  mMVM->HandleDOMMetaAdded();
+
+  // Perform an initial viewport computation and reflow, and
+  // sanity-check the results.
+  mMVM->SetInitialViewport();
+  EXPECT_EQ(CSSSize(300, 600), mMVMContext->GetICBSize());
+  EXPECT_EQ(CSSSize(600, 1200), mMVMContext->GetContentSize());
+  EXPECT_EQ(0.5f, mMVMContext->GetResolution());
+
+  // Rotate to landscape.
+  Resize(LayoutDeviceIntSize(600, 300));
+  EXPECT_EQ(CSSSize(600, 300), mMVMContext->GetICBSize());
+  EXPECT_EQ(CSSSize(600, 1200), mMVMContext->GetContentSize());
+  EXPECT_EQ(1.0f, mMVMContext->GetResolution());
+
+  // Rotate back to portrait and check that we have returned
+  // to the portrait resolution.
+  Resize(LayoutDeviceIntSize(300, 600));
+  EXPECT_EQ(CSSSize(300, 600), mMVMContext->GetICBSize());
+  EXPECT_EQ(CSSSize(600, 1200), mMVMContext->GetContentSize());
+  EXPECT_EQ(0.5f, mMVMContext->GetResolution());
+}
diff --git a/gfx/layers/apz/test/gtest/mvm/moz.build b/gfx/layers/apz/test/gtest/mvm/moz.build
new file mode 100644
index 0000000000..0fa985307b
--- /dev/null
+++ b/gfx/layers/apz/test/gtest/mvm/moz.build
@@ -0,0 +1,13 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+UNIFIED_SOURCES += [
+    "TestMobileViewportManager.cpp",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul-gtest"