Oilpan: have URL object on the heap.

Source/core/dom/URL.idl

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  * Copyright (C) 2012 Motorola Mobility Inc.
  *
  * 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 15 matching lines @@
 
 // http://url.spec.whatwg.org/#url
 
 [
     Constructor(USVString url),
     Constructor(USVString url, USVString base),
     Constructor(USVString url, URL base),
     Exposed=(Window,Worker),
     ImplementedAs=DOMURL,
     RaisesException=Constructor,
-    WillBeGarbageCollected,
+    GarbageCollected,
 ] interface URL {
     // FIXME: should be in separate URLBlob.idl partial interface definition
     // http://dev.w3.org/2006/webapi/FileAPI/#URL-object
     // FIXME: should not be nullable
     [RaisesException, CallWith=ExecutionContext] static DOMString? createObjectURL(Blob? blob);
     [CallWith=ExecutionContext] static void revokeObjectURL(DOMString url);
 };
 
 URL implements URLUtils;