Provide proper Dartium support for _getNewIsolateId().

lib/dom/templates/html/dartium/html_dartium.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.
 
 // DO NOT EDIT
 // Auto-generated dart:html library.
 
 #library("html");
 
 #import("dart:isolate");
@@ skipping 49 matching lines @@
 
 Element query(String selector) => _document.query(selector);
 ElementList queryAll(String selector) => _document.queryAll(selector);
 
 class _Null {
   const _Null();
 }
 
 final _null = const _Null();
 
-int _getNewIsolateId() {
-  // TODO(vsm): We need a Dartium native for this.
-  return 1;
-}
+int _getNewIsolateId() => _Utils._getNewIsolateId();
 
 bool _callPortInitialized = false;
 var _callPortLastResult = null;
 
 _callPortSync(num id, var message) {
   if (!_callPortInitialized) {
     window.on['js-result'].add((event) {
       _callPortLastResult = JSON.parse(event.data);
     }, false);
     _callPortInitialized = true;
   }
   assert(_callPortLastResult == null);
   _dispatchEvent('js-sync-message', {'id': id, 'message': message});
   var result = _callPortLastResult;
   _callPortLastResult = null;
   return result;
 }