anchor.diff:    Stream<ServiceActionEvent> onIsolateResponse(String callId) {
       // TODO(ericarnold): Implement
       StreamSubscription subscription;
  -    StreamController<ActionEvent> controller =
  -        new StreamController<ActionEvent>();
  -    subscription = onIsolateMessage.listen((ActionEvent event){
  +    StreamController<ServiceActionEvent> controller =
  +        new StreamController<ServiceActionEvent>();
  +    subscription = onIsolateMessage.listen((ServiceActionEvent event){
         if (event.response && event.callId == callId) {
           subscription.cancel();
           controller..add(event)..close();
  
positive.code: 
  class ExampleService extends Service {
    String serviceId = "example";
    ExampleService(Services services, _IsolateHandler handler)
        : super(services, handler);
  }
  
negative.code:         _sendPort = arg;
          _readyController..add(null)..close();
        } else {
          if (arg is int) {
            // int: handle as ping
            _pong(arg);
          } else if (arg is String) {
            // String: handle as print
            print ("Worker: $arg");
          } else {
            // implemented ...
            String data = arg["data"];
            Map dataMap = null;
            if (data != null) {
              dataMap = JSON.decode(data);
            }
            ServiceActionEvent event = new ServiceActionEvent(
                arg["serviceId"], arg["actionId"], arg["callId"], dataMap);
            _messageController..add(event);
          }
        }
      });
  
  