Merging upstream version 127.0.

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

14 files changed, 230 insertions, 103 deletions

diff --git a/gfx/layers/ipc/APZCTreeManagerChild.cpp b/gfx/layers/ipc/APZCTreeManagerChild.cpp
index b7f50c1c92..5dec4ca065 100644
--- a/gfx/layers/ipc/APZCTreeManagerChild.cpp
+++ b/gfx/layers/ipc/APZCTreeManagerChild.cpp
@@ -31,6 +31,9 @@ void APZCTreeManagerChild::SetCompositorSession(
   // we're setting mCompositorSession or we're clearing it).
   MOZ_ASSERT(!mCompositorSession ^ !aSession);
   mCompositorSession = aSession;
+  if (mInputBridge) {
+    mInputBridge->SetCompositorSession(aSession);
+  }
 }
 
 void APZCTreeManagerChild::SetInputBridge(APZInputBridgeChild* aInputBridge) {
@@ -143,45 +146,6 @@ void APZCTreeManagerChild::ActorDestroy(ActorDestroyReason aWhy) {
   mIPCOpen = false;
 }
 
-mozilla::ipc::IPCResult APZCTreeManagerChild::RecvHandleTap(
-    const TapType& aType, const LayoutDevicePoint& aPoint,
-    const Modifiers& aModifiers, const ScrollableLayerGuid& aGuid,
-    const uint64_t& aInputBlockId,
-    const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics) {
-  MOZ_ASSERT(XRE_IsParentProcess());
-  if (mCompositorSession &&
-      mCompositorSession->RootLayerTreeId() == aGuid.mLayersId &&
-      mCompositorSession->GetContentController()) {
-    RefPtr<GeckoContentController> controller =
-        mCompositorSession->GetContentController();
-    controller->HandleTap(aType, aPoint, aModifiers, aGuid, aInputBlockId,
-                          aDoubleTapToZoomMetrics);
-    return IPC_OK();
-  }
-  dom::BrowserParent* tab =
-      dom::BrowserParent::GetBrowserParentFromLayersId(aGuid.mLayersId);
-  if (tab) {
-#ifdef MOZ_WIDGET_ANDROID
-    // On Android, touch events are dispatched from the UI thread to the main
-    // thread using the Android priority queue. It is possible that this tap has
-    // made it to the GPU process and back before they have been processed. We
-    // must therefore dispatch this message to the same queue, otherwise the tab
-    // may receive the tap event before the touch events that synthesized it.
-    mozilla::jni::DispatchToGeckoPriorityQueue(
-        NewRunnableMethod<TapType, LayoutDevicePoint, Modifiers,
-                          ScrollableLayerGuid, uint64_t,
-                          Maybe<DoubleTapToZoomMetrics>>(
-            "dom::BrowserParent::SendHandleTap", tab,
-            &dom::BrowserParent::SendHandleTap, aType, aPoint, aModifiers,
-            aGuid, aInputBlockId, aDoubleTapToZoomMetrics));
-#else
-    tab->SendHandleTap(aType, aPoint, aModifiers, aGuid, aInputBlockId,
-                       aDoubleTapToZoomMetrics);
-#endif
-  }
-  return IPC_OK();
-}
-
 mozilla::ipc::IPCResult APZCTreeManagerChild::RecvNotifyPinchGesture(
     const PinchGestureType& aType, const ScrollableLayerGuid& aGuid,
     const LayoutDevicePoint& aFocusPoint, const LayoutDeviceCoord& aSpanChange,
diff --git a/gfx/layers/ipc/APZCTreeManagerChild.h b/gfx/layers/ipc/APZCTreeManagerChild.h
index 756677e1e3..4d79a18d5a 100644
--- a/gfx/layers/ipc/APZCTreeManagerChild.h
+++ b/gfx/layers/ipc/APZCTreeManagerChild.h
@@ -73,13 +73,6 @@ class APZCTreeManagerChild : public IAPZCTreeManager,
   void ActorDestroy(ActorDestroyReason aWhy) override;
 
  protected:
-  MOZ_CAN_RUN_SCRIPT_BOUNDARY
-  mozilla::ipc::IPCResult RecvHandleTap(
-      const TapType& aType, const LayoutDevicePoint& aPoint,
-      const Modifiers& aModifiers, const ScrollableLayerGuid& aGuid,
-      const uint64_t& aInputBlockId,
-      const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics);
-
   mozilla::ipc::IPCResult RecvNotifyPinchGesture(
       const PinchGestureType& aType, const ScrollableLayerGuid& aGuid,
       const LayoutDevicePoint& aFocusPoint,
diff --git a/gfx/layers/ipc/APZInputBridgeChild.cpp b/gfx/layers/ipc/APZInputBridgeChild.cpp
index bf059143ec..f9de8575a6 100644
--- a/gfx/layers/ipc/APZInputBridgeChild.cpp
+++ b/gfx/layers/ipc/APZInputBridgeChild.cpp
@@ -12,6 +12,14 @@
 #include "mozilla/layers/APZThreadUtils.h"
 #include "mozilla/layers/SynchronousTask.h"
 
+#include "mozilla/layers/GeckoContentController.h"  // for GeckoContentController
+#include "mozilla/layers/DoubleTapToZoom.h"  // for DoubleTapToZoomMetrics
+#include "mozilla/layers/RemoteCompositorSession.h"  // for RemoteCompositorSession
+#include "mozilla/dom/BrowserParent.h"               // for BrowserParent
+#ifdef MOZ_WIDGET_ANDROID
+#  include "mozilla/jni/Utils.h"  // for DispatchToGeckoPriorityQueue
+#endif
+
 namespace mozilla {
 namespace layers {
 
@@ -31,13 +39,20 @@ RefPtr<APZInputBridgeChild> APZInputBridgeChild::Create(
 }
 
 APZInputBridgeChild::APZInputBridgeChild(const uint64_t& aProcessToken)
-    : mIsOpen(false), mProcessToken(aProcessToken) {
+    : mIsOpen(false),
+      mProcessToken(aProcessToken),
+      mCompositorSession(nullptr) {
   MOZ_ASSERT(XRE_IsParentProcess());
   MOZ_ASSERT(NS_IsMainThread());
 }
 
 APZInputBridgeChild::~APZInputBridgeChild() = default;
 
+void APZInputBridgeChild::SetCompositorSession(
+    RemoteCompositorSession* aSession) {
+  mCompositorSession = aSession;
+}
+
 void APZInputBridgeChild::Open(Endpoint<PAPZInputBridgeChild>&& aEndpoint) {
   APZThreadUtils::AssertOnControllerThread();
 
@@ -176,6 +191,63 @@ APZEventResult APZInputBridgeChild::ReceiveInputEvent(
   return res;
 }
 
+void APZInputBridgeChild::HandleTapOnMainThread(
+    const TapType& aType, const LayoutDevicePoint& aPoint,
+    const Modifiers& aModifiers, const ScrollableLayerGuid& aGuid,
+    const uint64_t& aInputBlockId,
+    const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics) {
+  if (mCompositorSession &&
+      mCompositorSession->RootLayerTreeId() == aGuid.mLayersId &&
+      mCompositorSession->GetContentController()) {
+    RefPtr<GeckoContentController> controller =
+        mCompositorSession->GetContentController();
+    controller->HandleTap(aType, aPoint, aModifiers, aGuid, aInputBlockId,
+                          aDoubleTapToZoomMetrics);
+    return;
+  }
+  dom::BrowserParent* tab =
+      dom::BrowserParent::GetBrowserParentFromLayersId(aGuid.mLayersId);
+  if (tab) {
+#ifdef MOZ_WIDGET_ANDROID
+    // On Android, touch events are dispatched from the UI thread to the main
+    // thread using the Android priority queue. It is possible that this tap has
+    // made it to the GPU process and back before they have been processed. We
+    // must therefore dispatch this message to the same queue, otherwise the tab
+    // may receive the tap event before the touch events that synthesized it.
+    mozilla::jni::DispatchToGeckoPriorityQueue(
+        NewRunnableMethod<TapType, LayoutDevicePoint, Modifiers,
+                          ScrollableLayerGuid, uint64_t,
+                          Maybe<DoubleTapToZoomMetrics>>(
+            "dom::BrowserParent::SendHandleTap", tab,
+            &dom::BrowserParent::SendHandleTap, aType, aPoint, aModifiers,
+            aGuid, aInputBlockId, aDoubleTapToZoomMetrics));
+#else
+    tab->SendHandleTap(aType, aPoint, aModifiers, aGuid, aInputBlockId,
+                       aDoubleTapToZoomMetrics);
+#endif
+  }
+}
+
+mozilla::ipc::IPCResult APZInputBridgeChild::RecvHandleTap(
+    const TapType& aType, const LayoutDevicePoint& aPoint,
+    const Modifiers& aModifiers, const ScrollableLayerGuid& aGuid,
+    const uint64_t& aInputBlockId,
+    const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics) {
+  if (NS_IsMainThread()) {
+    HandleTapOnMainThread(aType, aPoint, aModifiers, aGuid, aInputBlockId,
+                          aDoubleTapToZoomMetrics);
+  } else {
+    NS_DispatchToMainThread(
+        NewRunnableMethod<TapType, LayoutDevicePoint, Modifiers,
+                          ScrollableLayerGuid, uint64_t,
+                          Maybe<DoubleTapToZoomMetrics>>(
+            "layers::APZInputBridgeChild::HandleTapOnMainThread", this,
+            &APZInputBridgeChild::HandleTapOnMainThread, aType, aPoint,
+            aModifiers, aGuid, aInputBlockId, aDoubleTapToZoomMetrics));
+  }
+  return IPC_OK();
+}
+
 mozilla::ipc::IPCResult APZInputBridgeChild::RecvCallInputBlockCallback(
     uint64_t aInputBlockId, const APZHandledResult& aHandledResult) {
   auto it = mInputBlockCallbacks.find(aInputBlockId);
diff --git a/gfx/layers/ipc/APZInputBridgeChild.h b/gfx/layers/ipc/APZInputBridgeChild.h
index dd77d95f36..4b14e3aa0d 100644
--- a/gfx/layers/ipc/APZInputBridgeChild.h
+++ b/gfx/layers/ipc/APZInputBridgeChild.h
@@ -10,11 +10,16 @@
 #include "mozilla/layers/APZInputBridge.h"
 #include "mozilla/layers/PAPZInputBridgeChild.h"
 
+#include "mozilla/layers/GeckoContentControllerTypes.h"
+
 namespace mozilla {
 namespace layers {
 
+class RemoteCompositorSession;
+
 class APZInputBridgeChild : public PAPZInputBridgeChild, public APZInputBridge {
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(APZInputBridgeChild, final)
+  using TapType = GeckoContentController_TapType;
 
  public:
   static RefPtr<APZInputBridgeChild> Create(
@@ -23,10 +28,19 @@ class APZInputBridgeChild : public PAPZInputBridgeChild, public APZInputBridge {
 
   void Destroy();
 
+  void SetCompositorSession(RemoteCompositorSession* aSession);
+
   APZEventResult ReceiveInputEvent(
       InputData& aEvent,
       InputBlockCallback&& aCallback = InputBlockCallback()) override;
 
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  mozilla::ipc::IPCResult RecvHandleTap(
+      const TapType& aType, const LayoutDevicePoint& aPoint,
+      const Modifiers& aModifiers, const ScrollableLayerGuid& aGuid,
+      const uint64_t& aInputBlockId,
+      const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics);
+
   mozilla::ipc::IPCResult RecvCallInputBlockCallback(
       uint64_t aInputBlockId, const APZHandledResult& handledResult);
 
@@ -48,8 +62,16 @@ class APZInputBridgeChild : public PAPZInputBridgeChild, public APZInputBridge {
  private:
   void Open(Endpoint<PAPZInputBridgeChild>&& aEndpoint);
 
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void HandleTapOnMainThread(
+      const TapType& aType, const LayoutDevicePoint& aPoint,
+      const Modifiers& aModifiers, const ScrollableLayerGuid& aGuid,
+      const uint64_t& aInputBlockId,
+      const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics);
+
   bool mIsOpen;
   uint64_t mProcessToken;
+  MOZ_NON_OWNING_REF RemoteCompositorSession* mCompositorSession = nullptr;
 
   using InputBlockCallbackMap =
       std::unordered_map<uint64_t, InputBlockCallback>;
diff --git a/gfx/layers/ipc/APZInputBridgeParent.cpp b/gfx/layers/ipc/APZInputBridgeParent.cpp
index fcc642ff7a..475c15abca 100644
--- a/gfx/layers/ipc/APZInputBridgeParent.cpp
+++ b/gfx/layers/ipc/APZInputBridgeParent.cpp
@@ -16,14 +16,15 @@ namespace mozilla {
 namespace layers {
 
 /* static */
-RefPtr<APZInputBridgeParent> APZInputBridgeParent::Create(
+APZInputBridgeParent* APZInputBridgeParent::Create(
     const LayersId& aLayersId, Endpoint<PAPZInputBridgeParent>&& aEndpoint) {
-  RefPtr<APZInputBridgeParent> parent = new APZInputBridgeParent(aLayersId);
+  APZInputBridgeParent* parent = new APZInputBridgeParent(aLayersId);
   if (!aEndpoint.Bind(parent)) {
     // We can't recover from this.
     MOZ_CRASH("Failed to bind APZInputBridgeParent to endpoint");
   }
 
+  CompositorBridgeParent::SetAPZInputBridgeParent(aLayersId, parent);
   return parent;
 }
 
@@ -31,6 +32,7 @@ APZInputBridgeParent::APZInputBridgeParent(const LayersId& aLayersId) {
   MOZ_ASSERT(XRE_IsGPUProcess());
   MOZ_ASSERT(NS_IsMainThread());
 
+  mLayersId = aLayersId;
   mTreeManager = CompositorBridgeParent::GetAPZCTreeManager(aLayersId);
   MOZ_ASSERT(mTreeManager);
 }
@@ -205,6 +207,10 @@ mozilla::ipc::IPCResult APZInputBridgeParent::RecvProcessUnhandledEvent(
 }
 
 void APZInputBridgeParent::ActorDestroy(ActorDestroyReason aWhy) {
+  StaticMonitorAutoLock lock(CompositorBridgeParent::sIndirectLayerTreesLock);
+  CompositorBridgeParent::LayerTreeState& state =
+      CompositorBridgeParent::sIndirectLayerTrees[mLayersId];
+  state.mApzInputBridgeParent = nullptr;
   // We shouldn't need it after this
   mTreeManager = nullptr;
 }
diff --git a/gfx/layers/ipc/APZInputBridgeParent.h b/gfx/layers/ipc/APZInputBridgeParent.h
index 71f43d092b..62e6427bb5 100644
--- a/gfx/layers/ipc/APZInputBridgeParent.h
+++ b/gfx/layers/ipc/APZInputBridgeParent.h
@@ -18,7 +18,7 @@ class APZInputBridgeParent : public PAPZInputBridgeParent {
   NS_INLINE_DECL_REFCOUNTING(APZInputBridgeParent, final)
 
  public:
-  static RefPtr<APZInputBridgeParent> Create(
+  static APZInputBridgeParent* Create(
       const LayersId& aLayersId, Endpoint<PAPZInputBridgeParent>&& aEndpoint);
 
   mozilla::ipc::IPCResult RecvReceiveMultiTouchInputEvent(
@@ -67,6 +67,7 @@ class APZInputBridgeParent : public PAPZInputBridgeParent {
 
  private:
   RefPtr<IAPZCTreeManager> mTreeManager;
+  LayersId mLayersId;
 };
 
 }  // namespace layers
diff --git a/gfx/layers/ipc/CanvasChild.cpp b/gfx/layers/ipc/CanvasChild.cpp
index a25d5e6799..efcd520300 100644
--- a/gfx/layers/ipc/CanvasChild.cpp
+++ b/gfx/layers/ipc/CanvasChild.cpp
@@ -206,13 +206,11 @@ class CanvasDataShmemHolder {
   }
 
   void Destroy() {
-    class DestroyRunnable final : public dom::WorkerRunnable {
+    class DestroyRunnable final : public dom::WorkerThreadRunnable {
      public:
       DestroyRunnable(dom::WorkerPrivate* aWorkerPrivate,
                       CanvasDataShmemHolder* aShmemHolder)
-          : dom::WorkerRunnable(aWorkerPrivate,
-                                "CanvasDataShmemHolder::Destroy",
-                                dom::WorkerRunnable::WorkerThread),
+          : dom::WorkerThreadRunnable("CanvasDataShmemHolder::Destroy"),
             mShmemHolder(aShmemHolder) {}
 
       bool WorkerRun(JSContext* aCx,
@@ -241,8 +239,9 @@ class CanvasDataShmemHolder {
       if (mWorkerRef) {
         if (!mWorkerRef->Private()->IsOnCurrentThread()) {
           auto task = MakeRefPtr<DestroyRunnable>(mWorkerRef->Private(), this);
+          dom::WorkerPrivate* worker = mWorkerRef->Private();
           mMutex.Unlock();
-          task->Dispatch();
+          task->Dispatch(worker);
           return;
         }
       } else if (!NS_IsMainThread()) {
diff --git a/gfx/layers/ipc/CanvasTranslator.cpp b/gfx/layers/ipc/CanvasTranslator.cpp
index 3fd7a4c4c4..46cab838de 100644
--- a/gfx/layers/ipc/CanvasTranslator.cpp
+++ b/gfx/layers/ipc/CanvasTranslator.cpp
@@ -1190,23 +1190,42 @@ already_AddRefed<gfx::SourceSurface> CanvasTranslator::LookupExternalSurface(
 // Check if the surface descriptor describes a GPUVideo texture for which we
 // only have an opaque source/handle from SurfaceDescriptorRemoteDecoder to
 // derive the actual texture from.
-static bool SDIsNullRemoteDecoder(const SurfaceDescriptor& sd) {
-  return sd.type() == SurfaceDescriptor::TSurfaceDescriptorGPUVideo &&
-         sd.get_SurfaceDescriptorGPUVideo()
-                 .get_SurfaceDescriptorRemoteDecoder()
-                 .subdesc()
-                 .type() == RemoteDecoderVideoSubDescriptor::Tnull_t;
+static bool SDIsSupportedRemoteDecoder(const SurfaceDescriptor& sd) {
+  if (sd.type() != SurfaceDescriptor::TSurfaceDescriptorGPUVideo) {
+    return false;
+  }
+
+  const auto& sdv = sd.get_SurfaceDescriptorGPUVideo();
+  const auto& sdvType = sdv.type();
+  if (sdvType != SurfaceDescriptorGPUVideo::TSurfaceDescriptorRemoteDecoder) {
+    return false;
+  }
+
+  const auto& sdrd = sdv.get_SurfaceDescriptorRemoteDecoder();
+  const auto& subdesc = sdrd.subdesc();
+  const auto& subdescType = subdesc.type();
+
+  if (subdescType == RemoteDecoderVideoSubDescriptor::Tnull_t ||
+      subdescType ==
+          RemoteDecoderVideoSubDescriptor::TSurfaceDescriptorMacIOSurface) {
+    return true;
+  }
+
+  return false;
 }
 
 already_AddRefed<gfx::SourceSurface>
 CanvasTranslator::LookupSourceSurfaceFromSurfaceDescriptor(
     const SurfaceDescriptor& aDesc) {
-  if (!SDIsNullRemoteDecoder(aDesc)) {
+  if (!SDIsSupportedRemoteDecoder(aDesc)) {
     return nullptr;
   }
 
   const auto& sdrd = aDesc.get_SurfaceDescriptorGPUVideo()
                          .get_SurfaceDescriptorRemoteDecoder();
+  const auto& subdesc = sdrd.subdesc();
+  const auto& subdescType = subdesc.type();
+
   RefPtr<VideoBridgeParent> parent =
       VideoBridgeParent::GetSingleton(sdrd.source());
   if (!parent) {
@@ -1222,9 +1241,19 @@ CanvasTranslator::LookupSourceSurfaceFromSurfaceDescriptor(
     return nullptr;
   }
 
-  RefPtr<gfx::DataSourceSurface> surf = texture->GetAsSurface();
+  if (subdescType ==
+      RemoteDecoderVideoSubDescriptor::TSurfaceDescriptorMacIOSurface) {
+    MOZ_ASSERT(texture->AsMacIOSurfaceTextureHost());
+    return texture->GetAsSurface();
+  }
+
+  if (subdescType == RemoteDecoderVideoSubDescriptor::Tnull_t) {
+    RefPtr<gfx::DataSourceSurface> surf = texture->GetAsSurface();
+    return surf.forget();
+  }
 
-  return surf.forget();
+  MOZ_ASSERT_UNREACHABLE("unexpected to be called");
+  return nullptr;
 }
 
 void CanvasTranslator::CheckpointReached() { CheckAndSignalWriter(); }
diff --git a/gfx/layers/ipc/CompositorBridgeParent.cpp b/gfx/layers/ipc/CompositorBridgeParent.cpp
index 767ea47b2f..d6efb2c991 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.cpp
+++ b/gfx/layers/ipc/CompositorBridgeParent.cpp
@@ -167,6 +167,7 @@ bool CompositorBridgeParentBase::DeallocShmem(ipc::Shmem& aShmem) {
 
 CompositorBridgeParent::LayerTreeState::LayerTreeState()
     : mApzcTreeManagerParent(nullptr),
+      mApzInputBridgeParent(nullptr),
       mParent(nullptr),
       mContentCompositorBridgeParent(nullptr) {}
 
@@ -645,9 +646,21 @@ bool CompositorBridgeParent::DeallocPAPZCTreeManagerParent(
   return true;
 }
 
+void CompositorBridgeParent::SetAPZInputBridgeParent(
+    const LayersId& aLayersId, APZInputBridgeParent* aInputBridgeParent) {
+  MOZ_RELEASE_ASSERT(XRE_IsGPUProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+  StaticMonitorAutoLock lock(CompositorBridgeParent::sIndirectLayerTreesLock);
+  CompositorBridgeParent::LayerTreeState& state =
+      CompositorBridgeParent::sIndirectLayerTrees[aLayersId];
+  MOZ_ASSERT(!state.mApzInputBridgeParent);
+  state.mApzInputBridgeParent = aInputBridgeParent;
+}
+
 void CompositorBridgeParent::AllocateAPZCTreeManagerParent(
     const StaticMonitorAutoLock& aProofOfLayerTreeStateLock,
     const LayersId& aLayersId, LayerTreeState& aState) {
+  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
   MOZ_ASSERT(aState.mParent == this);
   MOZ_ASSERT(mApzcTreeManager);
   MOZ_ASSERT(mApzUpdater);
@@ -1713,6 +1726,15 @@ APZCTreeManagerParent* CompositorBridgeParent::GetApzcTreeManagerParentForRoot(
 }
 
 /* static */
+APZInputBridgeParent* CompositorBridgeParent::GetApzInputBridgeParentForRoot(
+    LayersId aContentLayersId) {
+  StaticMonitorAutoLock lock(sIndirectLayerTreesLock);
+  CompositorBridgeParent::LayerTreeState* state =
+      GetStateForRoot(aContentLayersId, lock);
+  return state ? state->mApzInputBridgeParent : nullptr;
+}
+
+/* static */
 GeckoContentController*
 CompositorBridgeParent::GetGeckoContentControllerForRoot(
     LayersId aContentLayersId) {
diff --git a/gfx/layers/ipc/CompositorBridgeParent.h b/gfx/layers/ipc/CompositorBridgeParent.h
index 0e6bd48f9a..c7cb530989 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.h
+++ b/gfx/layers/ipc/CompositorBridgeParent.h
@@ -24,6 +24,7 @@
 #include "mozilla/layers/ISurfaceAllocator.h"  // for IShmemAllocator
 #include "mozilla/layers/LayersTypes.h"
 #include "mozilla/layers/PCompositorBridgeParent.h"
+#include "mozilla/layers/APZInputBridgeParent.h"
 #include "mozilla/webrender/WebRenderTypes.h"
 
 namespace mozilla {
@@ -394,6 +395,10 @@ class CompositorBridgeParent final : public CompositorBridgeParentBase,
     ~LayerTreeState();
     RefPtr<GeckoContentController> mController;
     APZCTreeManagerParent* mApzcTreeManagerParent;
+    // The mApzInputBridgeParent is only populated for LayerTreeState
+    // objects corresponding to root LayerIds (one for each top-level
+    // window).
+    APZInputBridgeParent* mApzInputBridgeParent;
     RefPtr<CompositorBridgeParent> mParent;
     RefPtr<WebRenderBridgeParent> mWrBridge;
     // Pointer to the ContentCompositorBridgeParent. Used by APZCs to share
@@ -438,6 +443,13 @@ class CompositorBridgeParent final : public CompositorBridgeParentBase,
       LayersId aContentLayersId);
 
   /**
+   * Same as the GetApzcTreeManagerParentForRoot function, but returns
+   * the APZInputBridge for the parent process.
+   */
+  static APZInputBridgeParent* GetApzInputBridgeParentForRoot(
+      LayersId aContentLayersId);
+
+  /**
    * Used by the profiler to denote when a vsync occured
    */
   static void PostInsertVsyncProfilerMarker(mozilla::TimeStamp aVsyncTimestamp);
@@ -454,6 +466,9 @@ class CompositorBridgeParent final : public CompositorBridgeParentBase,
       const StaticMonitorAutoLock& aProofOfLayerTreeStateLock,
       const LayersId& aLayersId, LayerTreeState& aLayerTreeStateToUpdate);
 
+  static void SetAPZInputBridgeParent(const LayersId& aLayersId,
+                                      APZInputBridgeParent* aInputBridgeParent);
+
   PAPZParent* AllocPAPZParent(const LayersId& aLayersId) override;
   bool DeallocPAPZParent(PAPZParent* aActor) override;
 
diff --git a/gfx/layers/ipc/PAPZCTreeManager.ipdl b/gfx/layers/ipc/PAPZCTreeManager.ipdl
index a08e2cfeb1..75cb04bea6 100644
--- a/gfx/layers/ipc/PAPZCTreeManager.ipdl
+++ b/gfx/layers/ipc/PAPZCTreeManager.ipdl
@@ -80,10 +80,6 @@ parent:
 
 child:
 
-  async HandleTap(GeckoContentController_TapType aType, LayoutDevicePoint point, Modifiers aModifiers,
-                  ScrollableLayerGuid aGuid, uint64_t aInputBlockId,
-                  DoubleTapToZoomMetrics? aDoubleTapToZoomMetrics);
-
   async NotifyPinchGesture(PinchGestureType aType, ScrollableLayerGuid aGuid,
                            LayoutDevicePoint aFocusPoint, LayoutDeviceCoord aSpanChange,
                            Modifiers aModifiers);
diff --git a/gfx/layers/ipc/PAPZInputBridge.ipdl b/gfx/layers/ipc/PAPZInputBridge.ipdl
index 7564757b28..35ca82c018 100644
--- a/gfx/layers/ipc/PAPZInputBridge.ipdl
+++ b/gfx/layers/ipc/PAPZInputBridge.ipdl
@@ -6,11 +6,15 @@
 include "ipc/nsGUIEventIPC.h";
 
 using mozilla::LayoutDeviceIntPoint from "Units.h";
+using mozilla::LayoutDevicePoint from "Units.h";
+using mozilla::layers::GeckoContentController_TapType from "mozilla/layers/GeckoContentControllerTypes.h";
+using mozilla::layers::DoubleTapToZoomMetrics from "mozilla/layers/DoubleTapToZoom.h";
 using struct mozilla::layers::ScrollableLayerGuid from "mozilla/layers/ScrollableLayerGuid.h";
 using struct mozilla::layers::APZEventResult from "mozilla/layers/APZInputBridge.h";
 using struct mozilla::layers::APZHandledResult from "mozilla/layers/APZInputBridge.h";
 
 using mozilla::EventMessage from "mozilla/EventForwards.h";
+using mozilla::Modifiers from "mozilla/EventForwards.h";
 using class mozilla::MultiTouchInput from "InputData.h";
 using class mozilla::MouseInput from "InputData.h";
 using class mozilla::PanGestureInput from "InputData.h";
@@ -82,6 +86,10 @@ parent:
 child:
   async CallInputBlockCallback(uint64_t aInputBlockId,
                                APZHandledResult aHandledResult);
+
+  async HandleTap(GeckoContentController_TapType aType, LayoutDevicePoint point,
+                  Modifiers aModifiers, ScrollableLayerGuid aGuid,
+                  uint64_t aInputBlockId, DoubleTapToZoomMetrics? aDoubleTapToZoomMetrics);
 };
 
 } // namespace gfx
diff --git a/gfx/layers/ipc/RemoteContentController.cpp b/gfx/layers/ipc/RemoteContentController.cpp
index 682331362b..8c6ab22acd 100644
--- a/gfx/layers/ipc/RemoteContentController.cpp
+++ b/gfx/layers/ipc/RemoteContentController.cpp
@@ -62,7 +62,7 @@ void RemoteContentController::RequestContentRepaint(
   }
 }
 
-void RemoteContentController::HandleTapOnMainThread(
+void RemoteContentController::HandleTapOnParentProcessMainThread(
     TapType aTapType, LayoutDevicePoint aPoint, Modifiers aModifiers,
     ScrollableLayerGuid aGuid, uint64_t aInputBlockId,
     const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics) {
@@ -78,20 +78,19 @@ void RemoteContentController::HandleTapOnMainThread(
   }
 }
 
-void RemoteContentController::HandleTapOnCompositorThread(
+void RemoteContentController::HandleTapOnGPUProcessMainThread(
     TapType aTapType, LayoutDevicePoint aPoint, Modifiers aModifiers,
     ScrollableLayerGuid aGuid, uint64_t aInputBlockId,
     const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics) {
   MOZ_ASSERT(XRE_IsGPUProcess());
-  MOZ_ASSERT(mCompositorThread->IsOnCurrentThread());
+  MOZ_ASSERT(NS_IsMainThread());
 
-  // The raw pointer to APZCTreeManagerParent is ok here because we are on
-  // the compositor thread.
-  APZCTreeManagerParent* apzctmp =
-      CompositorBridgeParent::GetApzcTreeManagerParentForRoot(aGuid.mLayersId);
-  if (apzctmp) {
-    Unused << apzctmp->SendHandleTap(aTapType, aPoint, aModifiers, aGuid,
-                                     aInputBlockId, aDoubleTapToZoomMetrics);
+  // Send a message to the controller thread to handle the single-tap gesture.
+  APZInputBridgeParent* apzib =
+      CompositorBridgeParent::GetApzInputBridgeParentForRoot(aGuid.mLayersId);
+  if (apzib) {
+    Unused << apzib->SendHandleTap(aTapType, aPoint, aModifiers, aGuid,
+                                   aInputBlockId, aDoubleTapToZoomMetrics);
   }
 }
 
@@ -103,19 +102,18 @@ void RemoteContentController::HandleTap(
   APZThreadUtils::AssertOnControllerThread();
 
   if (XRE_GetProcessType() == GeckoProcessType_GPU) {
-    if (mCompositorThread->IsOnCurrentThread()) {
-      HandleTapOnCompositorThread(aTapType, aPoint, aModifiers, aGuid,
-                                  aInputBlockId, aDoubleTapToZoomMetrics);
+    if (NS_IsMainThread()) {
+      HandleTapOnGPUProcessMainThread(aTapType, aPoint, aModifiers, aGuid,
+                                      aInputBlockId, aDoubleTapToZoomMetrics);
     } else {
-      // We have to send messages from the compositor thread
-      mCompositorThread->Dispatch(
-          NewRunnableMethod<TapType, LayoutDevicePoint, Modifiers,
-                            ScrollableLayerGuid, uint64_t,
-                            Maybe<DoubleTapToZoomMetrics>>(
-              "layers::RemoteContentController::HandleTapOnCompositorThread",
-              this, &RemoteContentController::HandleTapOnCompositorThread,
-              aTapType, aPoint, aModifiers, aGuid, aInputBlockId,
-              aDoubleTapToZoomMetrics));
+      NS_DispatchToMainThread(NewRunnableMethod<TapType, LayoutDevicePoint,
+                                                Modifiers, ScrollableLayerGuid,
+                                                uint64_t,
+                                                Maybe<DoubleTapToZoomMetrics>>(
+          "layers::RemoteContentController::HandleTapOnGPUProcessMainThread",
+          this, &RemoteContentController::HandleTapOnGPUProcessMainThread,
+          aTapType, aPoint, aModifiers, aGuid, aInputBlockId,
+          aDoubleTapToZoomMetrics));
     }
     return;
   }
@@ -123,8 +121,8 @@ void RemoteContentController::HandleTap(
   MOZ_ASSERT(XRE_IsParentProcess());
 
   if (NS_IsMainThread()) {
-    HandleTapOnMainThread(aTapType, aPoint, aModifiers, aGuid, aInputBlockId,
-                          aDoubleTapToZoomMetrics);
+    HandleTapOnParentProcessMainThread(aTapType, aPoint, aModifiers, aGuid,
+                                       aInputBlockId, aDoubleTapToZoomMetrics);
   } else {
     // We must be on Android, running on the Java UI thread
 #ifndef MOZ_WIDGET_ANDROID
@@ -138,13 +136,15 @@ void RemoteContentController::HandleTap(
     // using NS_DispatchToMainThread would post to a different message loop,
     // and introduces the possibility of this tap event getting processed
     // out of order with respect to the touch events that synthesized it.
-    mozilla::jni::DispatchToGeckoPriorityQueue(
-        NewRunnableMethod<TapType, LayoutDevicePoint, Modifiers,
-                          ScrollableLayerGuid, uint64_t,
-                          Maybe<DoubleTapToZoomMetrics>>(
-            "layers::RemoteContentController::HandleTapOnMainThread", this,
-            &RemoteContentController::HandleTapOnMainThread, aTapType, aPoint,
-            aModifiers, aGuid, aInputBlockId, aDoubleTapToZoomMetrics));
+    mozilla::jni::DispatchToGeckoPriorityQueue(NewRunnableMethod<
+                                               TapType, LayoutDevicePoint,
+                                               Modifiers, ScrollableLayerGuid,
+                                               uint64_t,
+                                               Maybe<DoubleTapToZoomMetrics>>(
+        "layers::RemoteContentController::HandleTapOnParentProcessMainThread",
+        this, &RemoteContentController::HandleTapOnParentProcessMainThread,
+        aTapType, aPoint, aModifiers, aGuid, aInputBlockId,
+        aDoubleTapToZoomMetrics));
 #endif
   }
 }
diff --git a/gfx/layers/ipc/RemoteContentController.h b/gfx/layers/ipc/RemoteContentController.h
index 7c2ef3789f..34f85004d2 100644
--- a/gfx/layers/ipc/RemoteContentController.h
+++ b/gfx/layers/ipc/RemoteContentController.h
@@ -98,12 +98,12 @@ class RemoteContentController : public GeckoContentController,
   nsCOMPtr<nsISerialEventTarget> mCompositorThread;
   bool mCanSend;
 
-  void HandleTapOnMainThread(
-      TapType aType, LayoutDevicePoint aPoint, Modifiers aModifiers,
+  void HandleTapOnParentProcessMainThread(
+      TapType aTapType, LayoutDevicePoint aPoint, Modifiers aModifiers,
       ScrollableLayerGuid aGuid, uint64_t aInputBlockId,
       const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics);
-  void HandleTapOnCompositorThread(
-      TapType aType, LayoutDevicePoint aPoint, Modifiers aModifiers,
+  void HandleTapOnGPUProcessMainThread(
+      TapType aTapType, LayoutDevicePoint aPoint, Modifiers aModifiers,
       ScrollableLayerGuid aGuid, uint64_t aInputBlockId,
       const Maybe<DoubleTapToZoomMetrics>& aDoubleTapToZoomMetrics);
   void NotifyPinchGestureOnCompositorThread(