Bug 1176954 part.1 Child process should notify its parent process when it dispatches composition or selection event into the DOM tree r=smaug

dom/ipc/PBrowser.ipdl

@@ -265,6 +265,13 @@ parent:
     prio(urgent) sync EndIMEComposition(bool cancel)
                         returns (bool noCompositionEvent, nsString composition);
 
+    /**
+     * OnEventNeedingAckReceived() is called when a child process dispatches a
+     * composition event or a selection event which is sent from the parent
+     * process.
+     */
+    prio(urgent) async OnEventNeedingAckReceived();
+
     /**
      * Tells chrome to start plugin IME.  If this results in a string getting
      * committed, the result is in aCommitted (otherwise aCommitted is empty).

dom/ipc/TabChild.cpp

@@ -2659,6 +2659,7 @@ TabChild::RecvKeyEvent(const nsString& aType,
 bool
 TabChild::RecvCompositionEvent(const WidgetCompositionEvent& event)
 {
+  unused << SendOnEventNeedingAckReceived();
   WidgetCompositionEvent localEvent(event);
   localEvent.widget = mPuppetWidget;
   APZCCallbackHelper::DispatchWidgetEvent(localEvent);
@@ -2668,6 +2669,7 @@ TabChild::RecvCompositionEvent(const WidgetCompositionEvent& event)
 bool
 TabChild::RecvSelectionEvent(const WidgetSelectionEvent& event)
 {
+  unused << SendOnEventNeedingAckReceived();
   WidgetSelectionEvent localEvent(event);
   localEvent.widget = mPuppetWidget;
   APZCCallbackHelper::DispatchWidgetEvent(localEvent);

dom/ipc/TabParent.cpp

@@ -2087,6 +2087,14 @@ TabParent::RecvNotifyIMEPositionChange(const ContentCache& aContentCache)
   return true;
 }
 
+bool
+TabParent::RecvOnEventNeedingAckReceived()
+{
+  // This is called when the child process receives WidgetCompositionEvent or
+  // WidgetSelectionEvent.
+  return true;
+}
+
 bool
 TabParent::RecvRequestFocus(const bool& aCanRaise)
 {

dom/ipc/TabParent.h

@@ -177,6 +177,7 @@ public:
     virtual bool RecvNotifyIMEMouseButtonEvent(const widget::IMENotification& aEventMessage,
                                                bool* aConsumedByIME) override;
     virtual bool RecvNotifyIMEPositionChange(const ContentCache& aContentCache) override;
+    virtual bool RecvOnEventNeedingAckReceived() override;
     virtual bool RecvEndIMEComposition(const bool& aCancel,
                                        bool* aNoCompositionEvent,
                                        nsString* aComposition) override;