Capture delayed events and cancel as necessary.

Tag #1052

layout/base/nsPresShell.h

@@ -617,6 +617,7 @@ protected:
   public:
     virtual ~DelayedEvent() { }
     virtual void Dispatch() { }
+    virtual bool IsKeyPressEvent() { return false; }
   };
 
   class DelayedInputEvent : public DelayedEvent
@@ -641,6 +642,7 @@ protected:
   {
   public:
     explicit DelayedKeyEvent(mozilla::WidgetKeyboardEvent* aEvent);
+    virtual bool IsKeyPressEvent() override;
   };
 
   // Check if aEvent is a mouse event and record the mouse location for later
@@ -951,6 +953,8 @@ protected:
   // Whether the widget has received a paint message yet.
   bool                      mHasReceivedPaintMessage : 1;
 
+  bool                      mIsLastKeyDownCanceled : 1;
+
   static bool               sDisableNonTestMouseEvents;
 };