Inherit EventTarget interface instead of duplicating its code

Source/core/xml/XMLHttpRequest.idl

 /*
  * Copyright (C) 2008, 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 23 matching lines @@
 //    FIXME: enable once support for json responseText is completed. (bug #73648)
 //    "json",
     "text"
 };
 
 [
     GlobalContext=Window&WorkerGlobalScope,
     ActiveDOMObject,
     Constructor,
     ConstructorCallWith=ScriptExecutionContext,
-    CustomConstructor(optional XMLHttpRequestOptions options),
-    EventTarget
-] interface XMLHttpRequest {
+    CustomConstructor(optional XMLHttpRequestOptions options)
+] interface XMLHttpRequest : EventTarget {
     // From XMLHttpRequestEventTarget
     // event handler attributes
     attribute EventListener onabort;
     attribute EventListener onerror;
     attribute EventListener onload;
     attribute EventListener onloadend;
     attribute EventListener onloadstart;
     attribute EventListener onprogress;
     attribute EventListener ontimeout;
 
@@ skipping 29 matching lines @@
     [GetterRaisesException] readonly attribute Document responseXML;
 
     [SetterRaisesException] attribute XMLHttpRequestResponseType responseType;
     [CustomGetter, GetterRaisesException] readonly attribute Object response;
 
     [GetterRaisesException] readonly attribute unsigned short status;
     [GetterRaisesException] readonly attribute DOMString statusText;
 
     // Extension
     void overrideMimeType(DOMString override);
-
-    // 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);
 };