Inherit EventTarget interface instead of duplicating its code

Source/modules/mediastream/RTCDTMFSender.h

Index: Source/modules/mediastream/RTCDTMFSender.h
diff --git a/Source/modules/mediastream/RTCDTMFSender.h b/Source/modules/mediastream/RTCDTMFSender.h
index 8f3819789a6e223760269348f784e9d6d20e0cc3..ef34cafef96137dac31c29df2ee4660d25cc01fc 100644
--- a/Source/modules/mediastream/RTCDTMFSender.h
+++ b/Source/modules/mediastream/RTCDTMFSender.h
@@ -39,7 +39,7 @@ class MediaStreamTrack;
 class RTCPeerConnectionHandler;
 class RTCDTMFSenderHandler;
 
-class RTCDTMFSender : public RefCounted<RTCDTMFSender>, public ScriptWrappable, public EventTarget, public RTCDTMFSenderHandlerClient, public ActiveDOMObject {
+class RTCDTMFSender : public EventTarget, public RefCounted<RTCDTMFSender>, public ScriptWrappable, public RTCDTMFSenderHandlerClient, public ActiveDOMObject {
 public:
     static PassRefPtr<RTCDTMFSender> create(ScriptExecutionContext*, RTCPeerConnectionHandler*, PassRefPtr<MediaStreamTrack>, ExceptionCode&);
     ~RTCDTMFSender();