Use metadata annotation @patch for patch classes

runtime/bin/io_service_patch.dart

 // Copyright (c) 2013, 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.
 
-patch class _IOService {
+@patch class _IOService {
   // Lazy initialize service ports, 32 per isolate.
   static const int _SERVICE_PORT_COUNT = 32;
   static List<SendPort> _servicePort = new List(_SERVICE_PORT_COUNT);
   static RawReceivePort _receivePort;
   static SendPort _replyToPort;
   static Map<int, Completer> _messageMap = {};
   static int _id = 0;
 
-  /* patch */ static Future _dispatch(int request, List data) {
+  /* @patch */ static Future _dispatch(int request, List data) {
     int id;
     do {
       id = _getNextId();
     } while (_messageMap.containsKey(id));
     int index = id % _SERVICE_PORT_COUNT;
     _initialize(index);
     var completer = new Completer();
     _messageMap[id] = completer;
     try {
       _servicePort[index].send([id, _replyToPort, request, data]);
@@ skipping 29 matching lines @@
     _receivePort = null;
   }
 
   static int _getNextId() {
     if (_id == 0x7FFFFFFF) _id = 0;
     return _id++;
   }
 
   static SendPort _newServicePort() native "IOService_NewServicePort";
 }