Inherit EventTarget interface instead of duplicating its code

Source/modules/encryptedmedia/MediaKeySession.idl

 /*
  * Copyright (C) 2013 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
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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 [
     Conditional=ENCRYPTED_MEDIA_V2,
-    EnabledAtRuntime=encryptedMedia,
-    EventTarget
-] interface MediaKeySession {
+    EnabledAtRuntime=encryptedMedia
+] interface MediaKeySession : EventTarget {
     // error state
     readonly attribute MediaKeyError error;
 
     // session properties
     readonly attribute DOMString keySystem;
     readonly attribute DOMString sessionId;
 
     // session operations
     [RaisesException] void update(Uint8Array key);
     void close();
     
     // EventListeners
     [EnabledAtRuntime=encryptedMedia] attribute EventListener onwebkitkeyadded;
     [EnabledAtRuntime=encryptedMedia] attribute EventListener onwebkitkeyerror;
     [EnabledAtRuntime=encryptedMedia] attribute EventListener onwebkitkeymessage;
-
-    // EventTarget interface
-    void addEventListener(DOMString type, 
-                          EventListener listener, 
-                          optional boolean useCapture);
-    void removeEventListener(DOMString type, 
-                             EventListener listener, 
-                             optional boolean useCapture);
-    [RaisesException] boolean dispatchEvent(Event evt);
 };