--- a/gfx/layers/apz/public/APZSampler.h
+++ b/gfx/layers/apz/public/APZSampler.h
@@ -2,16 +2,17 @@
 /* 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_APZSampler_h
 #define mozilla_layers_APZSampler_h
 
+#include "base/message_loop.h"
 #include "LayersTypes.h"
 #include "mozilla/layers/APZTestData.h"
 #include "mozilla/layers/AsyncCompositionManager.h" // for AsyncTransform
 #include "mozilla/Maybe.h"
 #include "nsTArray.h"
 #include "Units.h"
 
 namespace mozilla {
@@ -120,16 +121,26 @@ public:
    */
   void RunOnSamplerThread(already_AddRefed<Runnable> aTask);
 
   /**
    * Returns true if currently on the APZSampler's "sampler thread".
    */
   bool IsSamplerThread();
 
+  /**
+   * Dispatches the given task to the APZ "controller thread", but does it *from*
+   * the sampler thread. That is, if the thread on which this function is called
+   * is not the sampler thread, the task is first dispatched to the sampler thread.
+   * When the sampler thread runs it (or if this is called directly on the sampler
+   * thread), that is when the task gets dispatched to the controller thread.
+   * The controller thread then actually runs the task.
+   */
+  void RunOnControllerThread(already_AddRefed<Runnable> aTask);
+
 protected:
   virtual ~APZSampler();
 
 private:
   RefPtr<APZCTreeManager> mApz;
 };
 
 } // namespace layers

--- a/gfx/layers/apz/src/APZSampler.cpp
+++ b/gfx/layers/apz/src/APZSampler.cpp
@@ -247,10 +247,21 @@ APZSampler::RunOnSamplerThread(already_A
 }
 
 bool
 APZSampler::IsSamplerThread()
 {
   return CompositorThreadHolder::IsInCompositorThread();
 }
 
+void
+APZSampler::RunOnControllerThread(already_AddRefed<Runnable> aTask)
+{
+  MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
+
+  RunOnSamplerThread(NewRunnableFunction(
+      "APZSampler::RunOnControllerThread",
+      &APZThreadUtils::RunOnControllerThread,
+      Move(aTask)));
+}
+
 } // namespace layers
 } // namespace mozilla

--- a/gfx/layers/ipc/APZCTreeManagerParent.cpp
+++ b/gfx/layers/ipc/APZCTreeManagerParent.cpp
@@ -38,17 +38,17 @@ APZCTreeManagerParent::ChildAdopted(RefP
   MOZ_ASSERT(aAPZSampler->HasTreeManager(aAPZCTreeManager));
   mTreeManager = aAPZCTreeManager;
   mSampler = aAPZSampler;
 }
 
 mozilla::ipc::IPCResult
 APZCTreeManagerParent::RecvSetKeyboardMap(const KeyboardMap& aKeyboardMap)
 {
-  APZThreadUtils::RunOnControllerThread(NewRunnableMethod<KeyboardMap>(
+  mSampler->RunOnControllerThread(NewRunnableMethod<KeyboardMap>(
     "layers::IAPZCTreeManager::SetKeyboardMap",
     mTreeManager,
     &IAPZCTreeManager::SetKeyboardMap,
     aKeyboardMap));
 
   return IPC_OK();
 }
 
@@ -59,31 +59,31 @@ APZCTreeManagerParent::RecvZoomToRect(
     const uint32_t& aFlags)
 {
   if (aGuid.mLayersId != mLayersId) {
     // Guard against bad data from hijacked child processes
     NS_ERROR("Unexpected layers id in RecvZoomToRect; dropping message...");
     return IPC_FAIL_NO_REASON(this);
   }
 
-  APZThreadUtils::RunOnControllerThread(
+  mSampler->RunOnControllerThread(
     NewRunnableMethod<ScrollableLayerGuid, CSSRect, uint32_t>(
       "layers::IAPZCTreeManager::ZoomToRect",
       mTreeManager,
       &IAPZCTreeManager::ZoomToRect,
       aGuid, aRect, aFlags));
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 APZCTreeManagerParent::RecvContentReceivedInputBlock(
     const uint64_t& aInputBlockId,
     const bool& aPreventDefault)
 {
-  APZThreadUtils::RunOnControllerThread(NewRunnableMethod<uint64_t, bool>(
+  mSampler->RunOnControllerThread(NewRunnableMethod<uint64_t, bool>(
     "layers::IAPZCTreeManager::ContentReceivedInputBlock",
     mTreeManager,
     &IAPZCTreeManager::ContentReceivedInputBlock,
     aInputBlockId,
     aPreventDefault));
 
   return IPC_OK();
 }
@@ -95,17 +95,17 @@ APZCTreeManagerParent::RecvSetTargetAPZC
 {
   for (size_t i = 0; i < aTargets.Length(); i++) {
     if (aTargets[i].mLayersId != mLayersId) {
       // Guard against bad data from hijacked child processes
       NS_ERROR("Unexpected layers id in RecvSetTargetAPZC; dropping message...");
       return IPC_FAIL_NO_REASON(this);
     }
   }
-  APZThreadUtils::RunOnControllerThread(
+  mSampler->RunOnControllerThread(
     NewRunnableMethod<uint64_t,
                       StoreCopyPassByRRef<nsTArray<ScrollableLayerGuid>>>(
       "layers::IAPZCTreeManager::SetTargetAPZC",
       mTreeManager,
       &IAPZCTreeManager::SetTargetAPZC,
       aInputBlockId,
       aTargets));
 
@@ -125,30 +125,30 @@ APZCTreeManagerParent::RecvUpdateZoomCon
 
   mTreeManager->UpdateZoomConstraints(aGuid, aConstraints);
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 APZCTreeManagerParent::RecvSetDPI(const float& aDpiValue)
 {
-  APZThreadUtils::RunOnControllerThread(NewRunnableMethod<float>(
+  mSampler->RunOnControllerThread(NewRunnableMethod<float>(
     "layers::IAPZCTreeManager::SetDPI",
     mTreeManager,
     &IAPZCTreeManager::SetDPI,
     aDpiValue));
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 APZCTreeManagerParent::RecvSetAllowedTouchBehavior(
     const uint64_t& aInputBlockId,
     nsTArray<TouchBehaviorFlags>&& aValues)
 {
-  APZThreadUtils::RunOnControllerThread(
+  mSampler->RunOnControllerThread(
     NewRunnableMethod<uint64_t,
                       StoreCopyPassByRRef<nsTArray<TouchBehaviorFlags>>>(
       "layers::IAPZCTreeManager::SetAllowedTouchBehavior",
       mTreeManager,
       &IAPZCTreeManager::SetAllowedTouchBehavior,
       aInputBlockId,
       Move(aValues)));
 
@@ -161,17 +161,17 @@ APZCTreeManagerParent::RecvStartScrollba
     const AsyncDragMetrics& aDragMetrics)
 {
   if (aGuid.mLayersId != mLayersId) {
     // Guard against bad data from hijacked child processes
     NS_ERROR("Unexpected layers id in RecvStartScrollbarDrag; dropping message...");
     return IPC_FAIL_NO_REASON(this);
   }
 
-  APZThreadUtils::RunOnControllerThread(
+  mSampler->RunOnControllerThread(
     NewRunnableMethod<ScrollableLayerGuid, AsyncDragMetrics>(
       "layers::IAPZCTreeManager::StartScrollbarDrag",
       mTreeManager,
       &IAPZCTreeManager::StartScrollbarDrag,
       aGuid,
       aDragMetrics));
 
   return IPC_OK();
@@ -184,45 +184,45 @@ APZCTreeManagerParent::RecvStartAutoscro
 {
   // Unlike RecvStartScrollbarDrag(), this message comes from the parent
   // process (via nsBaseWidget::mAPZC) rather than from the child process
   // (via TabChild::mApzcTreeManager), so there is no need to check the
   // layers id against mLayersId (and in any case, it wouldn't match, because
   // mLayersId stores the parent process's layers id, while nsBaseWidget is
   // sending the child process's layers id).
 
-  APZThreadUtils::RunOnControllerThread(
+  mSampler->RunOnControllerThread(
       NewRunnableMethod<ScrollableLayerGuid, ScreenPoint>(
         "layers::IAPZCTreeManager::StartAutoscroll",
         mTreeManager,
         &IAPZCTreeManager::StartAutoscroll,
         aGuid, aAnchorLocation));
 
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 APZCTreeManagerParent::RecvStopAutoscroll(const ScrollableLayerGuid& aGuid)
 {
   // See RecvStartAutoscroll() for why we don't check the layers id.
 
-  APZThreadUtils::RunOnControllerThread(
+  mSampler->RunOnControllerThread(
       NewRunnableMethod<ScrollableLayerGuid>(
         "layers::IAPZCTreeManager::StopAutoscroll",
         mTreeManager,
         &IAPZCTreeManager::StopAutoscroll,
         aGuid));
 
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
 APZCTreeManagerParent::RecvSetLongTapEnabled(const bool& aLongTapEnabled)
 {
-  APZThreadUtils::RunOnControllerThread(
+  mSampler->RunOnControllerThread(
       NewRunnableMethod<bool>(
         "layers::IAPZCTreeManager::SetLongTapEnabled",
         mTreeManager,
         &IAPZCTreeManager::SetLongTapEnabled,
         aLongTapEnabled));
 
   return IPC_OK();
 }