Implement automatic loading of dart:core_native_fields library

bin/eventhandler.dart

 // Copyright (c) 2011, 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.
 
-class EventHandler extends EventHandlerNativeWrapper {
+class EventHandler extends NativeFieldWrapperClass1 {
   EventHandler() { }
 
   static void _start() {
     if (_eventHandler === null) {
       _eventHandler = new EventHandler();
       _eventHandler._doStart();
     }
   }
 
   void _doStart() native "EventHandler_Start";
 
   static _sendData(int id, ReceivePort receivePort, int data) {
     if (_eventHandler !== null) {
       _eventHandler._doSendData(id, receivePort, data);
     }
   }
 
 
   void _doSendData(int id, ReceivePort receivePort, int data)
       native "EventHandler_SendData";
 
   static EventHandler _eventHandler;
 }