Use "self" not "window" for Worker API.

dart/sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol;
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
@@ skipping 20477 matching lines @@
 // 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.
 
 
 @DomName('URL')
 class Url native "URL" {
 
   static String createObjectUrl(blob_OR_source_OR_stream) =>
       JS('String',
-         '(window.URL || window.webkitURL).createObjectURL(#)',
+         '(self.URL || self.webkitURL).createObjectURL(#)',
          blob_OR_source_OR_stream);
 
   static void revokeObjectUrl(String objectUrl) =>
       JS('void',
-         '(window.URL || window.webkitURL).revokeObjectURL(#)', objectUrl);
+         '(self.URL || self.webkitURL).revokeObjectURL(#)', objectUrl);
 
 }
 // 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.
 
 
 @DocsEditable
 @DomName('ValidityState')
 class ValidityState native "ValidityState" {
@@ skipping 7437 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }