Inherit EventTarget interface instead of duplicating its code

Source/modules/mediastream/RTCDataChannel.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
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  * modification, are permitted provided that the following conditions
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 [
-    NoInterfaceObject,
-    EventTarget
-] interface RTCDataChannel {
+    NoInterfaceObject
+] interface RTCDataChannel : EventTarget {
     readonly attribute DOMString label;
     readonly attribute boolean reliable;
     readonly attribute DOMString readyState;
     readonly attribute unsigned long bufferedAmount;
 
     [SetterRaisesException] attribute DOMString binaryType;
 
     [RaisesException] void send(ArrayBuffer data);
     [RaisesException] void send(ArrayBufferView data);
     [RaisesException] void send(Blob data);
     [RaisesException] void send(DOMString data);
 
     void close();
 
     attribute EventListener onopen;
     attribute EventListener onerror;
     attribute EventListener onclose;
     attribute EventListener onmessage;
-
-    // EventTarget interface
-    void addEventListener(DOMString type,
-                          EventListener listener,
-                          optional boolean useCapture);
-    void removeEventListener(DOMString type,
-                             EventListener listener,
-                             optional boolean useCapture);
-    [RaisesException] boolean dispatchEvent(Event event);
 };