Adding 'part of html' to all files which are used by dart:html.

sdk/lib/html/src/Isolates.dart

 // 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;
+
 _serialize(var message) {
   return new _JsSerializer().traverse(message);
 }
 
 class _JsSerializer extends _Serializer {
 
   visitSendPortSync(SendPortSync x) {
     if (x is _JsSendPortSync) return visitJsSendPortSync(x);
     if (x is _LocalSendPortSync) return visitLocalSendPortSync(x);
     if (x is _RemoteSendPortSync) return visitRemoteSendPortSync(x);
@@ skipping 176 matching lines @@
 }
 
 get _isolateId => ReceivePortSync._isolateId;
 
 void _dispatchEvent(String receiver, var message) {
   var event = new CustomEvent(receiver, false, false, JSON.stringify(message));
   window.$dom_dispatchEvent(event);
 }
 
 String _getPortSyncEventData(CustomEvent event) => event.detail;