Add use counters for EventSource.URL, WebSocket.URL.

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 19 matching lines @@
  */
 
 [
     ActiveDOMObject,
     Constructor(DOMString url, optional Dictionary eventSourceInit),
     ConstructorCallWith=ExecutionContext,
     GlobalContext=Window&WorkerGlobalScope,
     RaisesException=Constructor,
 ] interface EventSource : EventTarget {
 
-    readonly attribute DOMString URL; // Lowercased .url is the one in the spec, but leaving .URL for compatibility reasons.
+    [MeasureAs=EventSourceURL] 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 EventHandler onopen;
     attribute EventHandler onmessage;
     attribute EventHandler onerror;
     void close();
 };