Use @Native annotation on dart2js DOM native classes

tools/dom/templates/html/dart2js/impl_URL.darttemplate

 // 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.
 
 part of $LIBRARYNAME;
 
-$(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+$(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 
   static String createObjectUrl(blob_OR_source_OR_stream) =>
       JS('String',
          '(self.URL || self.webkitURL).createObjectURL(#)',
           blob_OR_source_OR_stream);
 
   static String createObjectUrlFromSource(MediaSource source) =>
       JS('String', '(self.URL || self.webkitURL).createObjectURL(#)', source);
   
   static String createObjectUrlFromStream(MediaStream stream) =>
       JS('String', '(self.URL || self.webkitURL).createObjectURL(#)', stream);
   
   static String createObjectUrlFromBlob(Blob blob) =>
       JS('String', '(self.URL || self.webkitURL).createObjectURL(#)', blob);
 
   static void revokeObjectUrl(String url) =>
       JS('void',
          '(self.URL || self.webkitURL).revokeObjectURL(#)', url);
 $!MEMBERS
 }