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

Source/core/events/MessageEvent.h

 /*
  * Copyright (C) 2007 Henry Mason (hmason@mac.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * 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
@@ skipping 95 matching lines @@
     ArrayBuffer* dataAsArrayBuffer() const { ASSERT(m_dataType == DataTypeArrayBuffer); return m_dataAsArrayBuffer.get(); }
 
     void setSerializedData(PassRefPtr<SerializedScriptValue> data)
     {
         ASSERT(!m_dataAsSerializedScriptValue);
         m_dataAsSerializedScriptValue = data;
     }
 
     void entangleMessagePorts(ExecutionContext*);
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     MessageEvent();
     MessageEvent(const AtomicString&, const MessageEventInit&);
     MessageEvent(const String& origin, const String& lastEventId, PassRefPtr<EventTarget> source, PassOwnPtr<MessagePortArray>);
     MessageEvent(PassRefPtr<SerializedScriptValue> data, const String& origin, const String& lastEventId, PassRefPtr<EventTarget> source, PassOwnPtr<MessagePortArray>);
     MessageEvent(PassRefPtr<SerializedScriptValue> data, const String& origin, const String& lastEventId, PassRefPtr<EventTarget> source, PassOwnPtr<MessagePortChannelArray>);
 
     explicit MessageEvent(const String& data, const String& origin);
     explicit MessageEvent(PassRefPtr<Blob> data, const String& origin);
     explicit MessageEvent(PassRefPtr<ArrayBuffer> data, const String& origin);
 
     DataType m_dataType;
     RefPtr<SerializedScriptValue> m_dataAsSerializedScriptValue;
     String m_dataAsString;
     RefPtr<Blob> m_dataAsBlob;
     RefPtr<ArrayBuffer> m_dataAsArrayBuffer;
     String m_origin;
     String m_lastEventId;
     RefPtr<EventTarget> m_source;
     // m_ports are the MessagePorts in an engtangled state, and m_channels are
     // the MessageChannels in a disentangled state. Only one of them can be
     // non-empty at a time. entangleMessagePorts() moves between the states.
     OwnPtr<MessagePortArray> m_ports;
     OwnPtr<MessagePortChannelArray> m_channels;
 };
 
 } // namespace WebCore
 
 #endif // MessageEvent_h