Update VM service to new isolate API

runtime/bin/vmservice/vmservice_io.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.
 
 library vmservice_io;
 
 import 'dart:io';
 import 'vmservice.dart';
 
 part 'server.dart';
 
-var _port;
+// The TCP port that the HTTP server listens on.
+int _port;
+
+// The receive port that isolate startup / shutdown messages are delivered on.
+RawReceivePort _receivePort;
 
 main() {
   // Create VmService.
   var service = new VMService();
+  _receivePort = service.receivePort;
   // Start HTTP server.
   var server = new Server(service, _port);
   server.startServer();
 }