Bug 1177018 - Send mouse move events generated via nsIPresShell::SynthesizeMouseMove() to the child process through a different IPDL message than real mouse move events. r=smaug

This avoids a real event being dropped in favour of a synthesized event via IPDL compression, which is important because synthesized events don't generate 'mousemove' DOM events.

--HG--
extra : rebase_source : 711341f7ae50583498854993028bbd9e1b1299cc
extra : source : c0e8553911e54232f060bbb284f936d81f73f411

dom/ipc/PBrowser.ipdl

@@ -634,6 +634,14 @@ child:
      * they are 'compressed' by dumping the oldest one.
      */
     RealMouseMoveEvent(WidgetMouseEvent event) compress;
+    /**
+     * Mouse move events with |reason == eSynthesized| are sent via a separate
+     * message because they do not generate DOM 'mousemove' events, and the
+     * 'compress' attribute on RealMouseMoveEvent() could result in a
+     * |reason == eReal| event being dropped in favour of an |eSynthesized|
+     * event, and thus a DOM 'mousemove' event to be lost.
+     */
+    SynthMouseMoveEvent(WidgetMouseEvent event);
     RealMouseButtonEvent(WidgetMouseEvent event);
     RealKeyEvent(WidgetKeyboardEvent event, MaybeNativeKeyBinding keyBinding);
     MouseWheelEvent(WidgetWheelEvent event, ScrollableLayerGuid aGuid, uint64_t aInputBlockId);

dom/ipc/TabChild.cpp

@@ -1856,6 +1856,12 @@ TabChild::RecvRealMouseMoveEvent(const WidgetMouseEvent& event)
   return RecvRealMouseButtonEvent(event);
 }
 
+bool
+TabChild::RecvSynthMouseMoveEvent(const WidgetMouseEvent& event)
+{
+  return RecvRealMouseButtonEvent(event);
+}
+
 bool
 TabChild::RecvRealMouseButtonEvent(const WidgetMouseEvent& event)
 {

dom/ipc/TabChild.h

@@ -334,6 +334,7 @@ public:
                                 const int32_t&  aModifiers,
                                 const bool&     aIgnoreRootScrollFrame) override;
     virtual bool RecvRealMouseMoveEvent(const mozilla::WidgetMouseEvent& event) override;
+    virtual bool RecvSynthMouseMoveEvent(const mozilla::WidgetMouseEvent& event) override;
     virtual bool RecvRealMouseButtonEvent(const mozilla::WidgetMouseEvent& event) override;
     virtual bool RecvRealDragEvent(const WidgetDragEvent& aEvent,
                                    const uint32_t& aDragAction,

dom/ipc/TabParent.cpp

@@ -1381,7 +1381,11 @@ bool TabParent::SendRealMouseEvent(WidgetMouseEvent& event)
   }
 
   if (NS_MOUSE_MOVE == event.mMessage) {
-    return SendRealMouseMoveEvent(event);
+    if (event.reason == WidgetMouseEvent::eSynthesized) {
+      return SendSynthMouseMoveEvent(event);
+    } else {
+      return SendRealMouseMoveEvent(event);
+    }
   }
   return SendRealMouseButtonEvent(event);
 }