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

Source/core/events/CustomEvent.h

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 42 matching lines @@
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
     SerializedScriptValue* serializedDetail() { return m_serializedDetail.get(); }
 
     void setSerializedDetail(PassRefPtr<SerializedScriptValue> detail)
     {
         ASSERT(!m_serializedDetail);
         m_serializedDetail = detail;
     }
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     CustomEvent();
     CustomEvent(const AtomicString& type, const CustomEventInit& initializer);
 
     RefPtr<SerializedScriptValue> m_serializedDetail;
 };
 
 } // namespace WebCore
 
 #endif // CustomEvent_h