anchor.diff:    Services() {
       _isolateHandler = new _IsolateHandler();
       registerService(new ExampleService(this, _isolateHandler));
  +    registerService(new PingService(this, _isolateHandler));
     }
   
     Future<String> ping() => _isolateHandler.ping();
  
positive.code:  * Special service for handling Chrome app calls that the isolate
   * cannot handle on its own.
   */
  class ExampleService extends Service {
    String serviceId = "example";
  
    ExampleService(Services services, _IsolateHandler handler)
        : super(services, handler);
  }
  
  /**
  
negative.code:       } else {
          // TODO(ericarnold): Temporary (encode ping command once implemented)
          _pong(arg);
  
          // implemented ...
          String data = arg["data"];
          Map dataMap = null;
          if (data != null) {
            dataMap = JSON.decode(data);
          }
          ActionEvent event = new ActionEvent(
              arg["serviceId"], arg["actionId"], arg["callId"], dataMap);
          messageController..add(event);
        }
      });
  
  