Events synthesized in the child process must be propagated back to the parent. (bug 1126090 part 3, r=smaug)

dom/base/nsDOMWindowUtils.cpp

@@ -1030,9 +1030,7 @@ nsDOMWindowUtils::SendWheelEvent(float aX,
 
   wheelEvent.refPoint = ToWidgetPoint(CSSPoint(aX, aY), offset, presContext);
 
-  nsEventStatus status;
-  nsresult rv = widget->DispatchEvent(&wheelEvent, status);
-  NS_ENSURE_SUCCESS(rv, rv);
+  widget->DispatchAPZAwareEvent(&wheelEvent);
 
   bool failedX = false;
   if ((aOptions & WHEEL_EVENT_EXPECTED_OVERFLOW_DELTA_X_ZERO) &&

dom/ipc/PBrowser.ipdl

@@ -484,6 +484,8 @@ parent:
      */
     async SetDimensions(uint32_t aFlags, int32_t aX, int32_t aY, int32_t aCx, int32_t aCy);
 
+    prio(high) sync SynthesizedMouseWheelEvent(WidgetWheelEvent event);
+
 child:
     /**
      * Notify the remote browser that it has been Show()n on this

dom/ipc/TabParent.cpp

@@ -1232,6 +1232,20 @@ bool TabParent::SendMouseWheelEvent(WidgetWheelEvent& event)
   return PBrowserParent::SendMouseWheelEvent(event, guid, blockId);
 }
 
+bool TabParent::RecvSynthesizedMouseWheelEvent(const mozilla::WidgetWheelEvent& aEvent)
+{
+  nsCOMPtr<nsIWidget> widget = GetWidget();
+  if (!widget) {
+    return true;
+  }
+
+  WidgetWheelEvent localEvent(aEvent);
+  localEvent.widget = widget;
+
+  widget->DispatchAPZAwareEvent(&localEvent);
+  return true;
+}
+
 static void
 DoCommandCallback(mozilla::Command aCommand, void* aData)
 {

dom/ipc/TabParent.h

@@ -231,6 +231,7 @@ public:
                                                const bool& aPreventDefault) MOZ_OVERRIDE;
     virtual bool RecvSetTargetAPZC(const uint64_t& aInputBlockId,
                                    nsTArray<ScrollableLayerGuid>&& aTargets) MOZ_OVERRIDE;
+    virtual bool RecvSynthesizedMouseWheelEvent(const mozilla::WidgetWheelEvent& aEvent) MOZ_OVERRIDE;
 
     virtual PColorPickerParent*
     AllocPColorPickerParent(const nsString& aTitle, const nsString& aInitialColor) MOZ_OVERRIDE;

widget/PuppetWidget.cpp

@@ -328,6 +328,30 @@ PuppetWidget::DispatchEvent(WidgetGUIEvent* event, nsEventStatus& aStatus)
 }
 
 
+nsEventStatus
+PuppetWidget::DispatchAPZAwareEvent(WidgetInputEvent* aEvent)
+{
+  if (!gfxPrefs::AsyncPanZoomEnabled()) {
+    nsEventStatus status = nsEventStatus_eIgnore;
+    DispatchEvent(aEvent, status);
+    return status;
+  }
+
+  if (!mTabChild) {
+    return nsEventStatus_eIgnore;
+  }
+
+  switch (aEvent->mClass) {
+    case eWheelEventClass:
+      mTabChild->SendSynthesizedMouseWheelEvent(*aEvent->AsWheelEvent());
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unsupported event type");
+  }
+
+  return nsEventStatus_eIgnore;
+}
+
 NS_IMETHODIMP_(bool)
 PuppetWidget::ExecuteNativeKeyBinding(NativeKeyBindingsType aType,
                                       const mozilla::WidgetKeyboardEvent& aEvent,

widget/PuppetWidget.h

@@ -128,6 +128,7 @@ public:
   void InitEvent(WidgetGUIEvent& aEvent, nsIntPoint* aPoint = nullptr);
 
   NS_IMETHOD DispatchEvent(WidgetGUIEvent* aEvent, nsEventStatus& aStatus) MOZ_OVERRIDE;
+  nsEventStatus DispatchAPZAwareEvent(WidgetInputEvent* aEvent) MOZ_OVERRIDE;
 
   NS_IMETHOD CaptureRollupEvents(nsIRollupListener* aListener,
                                  bool aDoCapture) MOZ_OVERRIDE