Inherit EventTarget interface instead of duplicating its code

Source/modules/mediastream/RTCDataChannel.h

 /*
  * Copyright (C) 2012 Google 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
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 23 matching lines @@
 namespace WebKit {
 struct WebRTCDataChannelInit;
 }
 
 namespace WebCore {
 
 class Blob;
 class RTCDataChannelHandler;
 class RTCPeerConnectionHandler;
 
-class RTCDataChannel : public RefCounted<RTCDataChannel>, public ScriptWrappable, public EventTarget, public RTCDataChannelHandlerClient {
+class RTCDataChannel : public EventTarget, public RefCounted<RTCDataChannel>, public ScriptWrappable, public RTCDataChannelHandlerClient {
 public:
     static PassRefPtr<RTCDataChannel> create(ScriptExecutionContext*, PassOwnPtr<RTCDataChannelHandler>);
     static PassRefPtr<RTCDataChannel> create(ScriptExecutionContext*, RTCPeerConnectionHandler*, const String& label, const WebKit::WebRTCDataChannelInit&, ExceptionCode&);
     ~RTCDataChannel();
 
     String label() const;
     bool reliable() const;
     String readyState() const;
     unsigned long bufferedAmount() const;
 
@@ skipping 52 matching lines @@
     };
     BinaryType m_binaryType;
 
     Timer<RTCDataChannel> m_scheduledEventTimer;
     Vector<RefPtr<Event> > m_scheduledEvents;
 };
 
 } // namespace WebCore
 
 #endif // RTCDataChannel_h