anchor.diff:   * Defines a class which handles all isolate setup and communication
    */
   class _IsolateHandler {
  +  int _topCallId = 0;
  +  Map<int, Completer> _serviceCallCompleters = {};
  +
     final String _workerPath = 'services_impl.dart';
     SendPort _sendPort;
     final ReceivePort _receivePort = new ReceivePort();
   
     // Fired when isolate responds to message
     Stream<ServiceActionEvent> onIsolateResponse(String callId) {
  +    onIsolateMessage = _messageController.stream;
  +    onceIsolateReady = _readyController.stream.first;
       // TODO(ericarnold): Implement
     }
  +
  +  StreamController<ServiceActionEvent> _messageController =
  +      new StreamController<ServiceActionEvent>.broadcast();
  +
  +  StreamController _readyController = new StreamController.broadcast();
   
     // Fired when isolate originates a message
     Stream onIsolateMessage;
  
positive.code:     registerService(new ExampleService(this, _isolateHandler));
    }
  
    Service getService(String serviceId) => _services[serviceId];
  
    void registerService(Service service) {
      _services[service.serviceId] = service;
    }
  
  }
  
  /**
  
negative.code:   }
  
    Future _startIsolate() {
      _receivePort.listen((arg) {
        if (_sendPort == null) {
          _sendPort = arg;
          _readyController..add(null)..close();
        } else {
          pong(arg);
        }
      });
  
      return Isolate.spawnUri(Uri.parse(_workerPath), [], _receivePort.sendPort);
    }
  
    Future<String> ping() {
      Completer<String> completer = new Completer();
      int callId = _topCallId;
      _serviceCallCompleters[callId] = completer;
  
      onceIsolateReady.then((_){
        _sendPort.send(callId);
      });
  
      _topCallId += 1;
      return completer.future;
    }
  
    Future pong(int id) {
      Completer completer = _serviceCallCompleters[id];
      _serviceCallCompleters.remove(id);
      completer.complete("pong");
      return completer.future;
    }
  
  
    Future<ServiceActionEvent> sendAction(String serviceId, String actionId,
        String callId, [String data = ""]) {
  