Add @JSName annotation for native fields and methods.

sdk/lib/html/templates/html/impl/impl_MutationObserver.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 html;
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
   void observe(Node target,
                {Map options,
@@ skipping 57 matching lines @@
     _observe(target, options);
   }
 $endif
 
 $if DART2JS
   static _createDict() => JS('var', '{}');
   static _add(m, String key, value) { JS('void', '#[#] = #', m, key, value); }
   static _fixupList(list) => list;  // TODO: Ensure is a JavaScript Array.
 
   // Call native function with no conversions.
-  void _call(target, options) native 'observe';
+  @JSName('observe')
+  void _call(target, options) native;
 $endif
 }