Inherit EventTarget interface instead of duplicating its code

Source/core/page/EventSource.idl

 /*
  * Copyright (C) 2009 Ericsson AB. All rights reserved.
  * Copyright (C) 2010, 2011 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.
@@ skipping 16 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
     GlobalContext=Window&WorkerGlobalScope,
     ActiveDOMObject,
     Constructor(DOMString url, optional Dictionary eventSourceInit),
     ConstructorCallWith=ScriptExecutionContext,
-    ConstructorRaisesException,
-    EventTarget
-] interface EventSource {
+    ConstructorRaisesException
+] interface EventSource : EventTarget {
 
     readonly attribute DOMString URL; // Lowercased .url is the one in the spec, but leaving .URL for compatibility reasons.
     readonly attribute DOMString url;
     readonly attribute boolean withCredentials;
 
     // ready state
     const unsigned short CONNECTING = 0;
     const unsigned short OPEN = 1;
     const unsigned short CLOSED = 2;
     readonly attribute unsigned short readyState;
 
     // networking
     attribute EventListener onopen;
     attribute EventListener onmessage;
     attribute EventListener onerror;
     void close();
-
-    // 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);
-
 };