Make dart:_vmservice a proper builtin library

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:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:isolate';
-import 'dart:vmservice';
+import 'dart:_vmservice';
 
 part 'loader.dart';
 part 'resources.dart';
 part 'server.dart';
 
 // The TCP ip/port that the HTTP server listens on.
 int _port;
 String _ip;
 // Should the HTTP server auto start?
 bool _autoStart;
@@ skipping 75 matching lines @@
   // else {
   //   var service = new VMService();
   //   service.onShutdown = _onShutdown;
   // }
   scriptLoadPort.handler = _processLoadRequest;
   // Register signal handler after a small delay to avoid stalling main
   // isolate startup.
   new Timer(_shortDelay, _registerSignalHandler);
   return scriptLoadPort;
 }