Make Event RefCountedGarbageCollected and implement trace() methods to the Event hierarcy

Source/core/events/GestureEvent.cpp

Index: Source/core/events/GestureEvent.cpp
diff --git a/Source/core/events/GestureEvent.cpp b/Source/core/events/GestureEvent.cpp
index d8e5ca187a3d1d389de6dfbf29ff4f7f9f18e24d..645b72a41ca4e0aaa04473378caa5a629625c352 100644
--- a/Source/core/events/GestureEvent.cpp
+++ b/Source/core/events/GestureEvent.cpp
@@ -94,6 +94,11 @@ GestureEvent::GestureEvent(const AtomicString& type, PassRefPtr<AbstractView> vi
 {
 }
 
+void GestureEvent::trace(Visitor* visitor)
+{
+    MouseRelatedEvent::trace(visitor);
+}
+
 GestureEventDispatchMediator::GestureEventDispatchMediator(PassRefPtr<GestureEvent> gestureEvent)
     : EventDispatchMediator(gestureEvent)
 {