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

Source/core/events/Event.h

Index: Source/core/events/Event.h
diff --git a/Source/core/events/Event.h b/Source/core/events/Event.h
index bc7ce5d83ad7b8ede6e8fb7f0d321d16b7e83b3e..d63cea615a7019095c310d16f23a3e9cbbb86fc6 100644
--- a/Source/core/events/Event.h
+++ b/Source/core/events/Event.h
@@ -44,7 +44,7 @@ struct EventInit {
     bool cancelable;
 };
 
-class Event : public ScriptWrappable, public RefCounted<Event> {
+class Event : public RefCountedWillBeRefCountedGarbageCollected<Event>,  public ScriptWrappable {
 public:
     enum PhaseType {
         NONE                = 0,
@@ -179,6 +179,8 @@ public:
 
     bool isBeingDispatched() const { return eventPhase(); }
 
+    virtual void trace(Visitor*);
+
 protected:
     Event();
     Event(const AtomicString& type, bool canBubble, bool cancelable);