Use metadata annotation @patch for patch classes

runtime/lib/vmservice_patch.dart

 // Copyright (c) 2015, 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 Asset {
+@patch class Asset {
   /// Call to request assets from the embedder.
-  /* patch */ static HashMap<String, Asset> request() {
+  /* @patch */ static HashMap<String, Asset> request() {
     HashMap<String, Asset> assets = new HashMap<String, Asset>();
     Uint8List tarBytes = _requestAssets();
     if (tarBytes == null) {
       return assets;
     }
     List assetList = _decodeAssets(tarBytes);
     for (int i = 0; i < assetList.length; i += 2) {
       var a = new Asset(assetList[i], assetList[i + 1]);
       assets[a.name] = a;
     }
     return assets;
   }
 }
 
 List _decodeAssets(Uint8List data) native "VMService_DecodeAssets";
 
-patch bool sendIsolateServiceMessage(SendPort sp, List m)
+@patch bool sendIsolateServiceMessage(SendPort sp, List m)
     native "VMService_SendIsolateServiceMessage";
-patch void sendRootServiceMessage(List m)
+@patch void sendRootServiceMessage(List m)
     native "VMService_SendRootServiceMessage";
-patch void sendObjectRootServiceMessage(List m)
+@patch void sendObjectRootServiceMessage(List m)
     native "VMService_SendObjectRootServiceMessage";
-patch void _onStart() native "VMService_OnStart";
-patch void _onExit() native "VMService_OnExit";
-patch void onServerAddressChange(String address)
+@patch void _onStart() native "VMService_OnStart";
+@patch void _onExit() native "VMService_OnExit";
+@patch void onServerAddressChange(String address)
     native "VMService_OnServerAddressChange";
-patch bool _vmListenStream(String streamId) native "VMService_ListenStream";
-patch void _vmCancelStream(String streamId) native "VMService_CancelStream";
-patch Uint8List _requestAssets() native "VMService_RequestAssets";
-patch void _spawnUriNotify(obj, String token)
+@patch bool _vmListenStream(String streamId) native "VMService_ListenStream";
+@patch void _vmCancelStream(String streamId) native "VMService_CancelStream";
+@patch Uint8List _requestAssets() native "VMService_RequestAssets";
+@patch void _spawnUriNotify(obj, String token)
     native "VMService_spawnUriNotify";