Mark DOMStringList.contains() as deprecated, add console warning.

Source/core/dom/DOMStringList.idl

 /*
  * Copyright (C) 2010 Google 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
@@ skipping 12 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://dom.spec.whatwg.org/#domstringlist
 
 // FIXME: DOMStringList has been removed from the spec. crbug.com/460726
 [
     WillBeGarbageCollected,
 ] interface DOMStringList {
     readonly attribute unsigned long length;
-    getter DOMString? item(unsigned long index);
-    [MeasureAs=DOMStringListContains] boolean contains(DOMString string);
+    [DeprecateAs=DOMStringListItem] DOMString? item(unsigned long index);
+    getter DOMString? (unsigned long index);
+    // FIXME: If Array.prototype.includes is added, add includes() and update deprecation message.

[philipj_slow, 2015/03/06 03:03:49]

I don't think it's a given that we'll want to add DOMStringList.includes or that
doing so would help the transition, so... remove this FIXME, wait and see?

[jsbell, 2015/03/06 17:19:20]

Done.

+    [DeprecateAs=DOMStringListContains] boolean contains(DOMString string);
 };