Implement @patch annotation for patch class members

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 {
   /// 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;
     }
@@ skipping 11 matching lines @@
     native "VMService_SendObjectRootServiceMessage";
 @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)
     native "VMService_spawnUriNotify";