anchor.diff:  
     // Fires when the isolate communication has been established.
     Stream onReady;
  -
  -  // Services:
  -  ExampleService exampleService;
  -  // ExampleService exampleService
  +  Map<String, Service> _services = {};
   
     Services() {
       _isolateHandler = new _IsolateHandler();
  -    exampleService = new ExampleService(_isolateHandler);
  +    registerService(new ExampleService(this, _isolateHandler));
     }
  +
  +  Service getService(String serviceId) => _services[serviceId];
  +
  +  void registerService(Service service) {
  +    _services[service.serviceId] = service;
  +  }
  +
   }
   
   /**
  
positive.code: abstract class Service {
    static int _topCallId = 0;
  
    _IsolateHandler _isolateHandler;
  
    String get serviceId;
  
    Service(this._isolateHandler);
  
    String _getNewCallId() => "host_${_topCallId++}";
  
  
negative.code:  */
  class ChromeService extends Service {
    String serviceId = "chrome";
    ChromeService(Services services, _IsolateHandler handler)
        : super(services, handler);
  
    // For incoming (non-requested) actions.
    void _receiveAction(ActionEvent event) {
  