Temporarily exposing createObjectUrl on Window.

tests/html/html.status

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 window_open_test: Fail, Pass # http://dartbug.com/5151
 
 event_test: Skip  # Issue 1996
 webgl_1_test: Skip  # Issue 1495
 xmldocument_test: Skip  # XML in dart:html is incomplete
 xmlelement_test: Skip  # XML in dart:html is incomplete
@@ skipping 152 matching lines @@
 [ $compiler == dart2js && $runtime == drt ]
 # Unknown error - should investigate.
 htmloptionscollection_test: Fail # Issue 3813.
 unknownelement_test: Fail # Issue 4189
 
 [ $compiler == dart2js && $runtime == none ]
 *: Fail, Pass # TODO(ahe): Triage these tests.
 
 [ $compiler == dart2js ]
 transferables_test: Skip # until isInstance works in dart2js
-url_test: Fail # antonm is working on it
 
 [ $compiler == dart2js && ($runtime == drt || $runtime == ff) ]
 request_animation_frame_test: Skip # Async test hangs.
 
 [ $compiler == dart2js && ($runtime == drt || $runtime == chrome || $runtime == ff) ]
 isolates_test: Skip   # Timeout because leg does not support web workers.
 typed_arrays_1_test: Fail # dart2js doesn't support is checks with generic types.
 
 [ $compiler == dart2js && $runtime == ff && $system == linux]
 indexeddb_3_test: Fail  # Caught Error: DATA_ERR: DOM IDBDatabase Exception 5 Error: The data provided does not meet the requirements of the function.
 
 [ $compiler == dart2js && $runtime == ff ]
 cache_test: Fail # Expectation: ApplicationCache. Caught NoSuchMethodError : method not found: 'get$status'
 xhr_test: Skip # Timeout
 inner_frame_test: Skip # Timeout
 svg_3_test: Skip # Timeout
 documentfragment_test: Skip # Timeout
 
 [ $compiler == dart2js && $runtime == chrome && $system == windows]
 css_test: Pass, Fail # Issue #2823
 
 [ $compiler == dart2js && $runtime == ff && $system == windows]
 js_interop_2_test: Fail # Issue 4658.
 
 [ $compiler == dart2js && $checked && $browser]
 fileapi_test: Fail # TypeError: Object #<DirectoryEntry> has no method 'get$name'
 cross_frame_test: Fail # Caught NoSuchMethodError : method not found: 'is$_WindowImpl'
 window_open_test: Fail # Caught NoSuchMethodError : method not found: 'is$_WindowImpl'