anchor.diff:          if (_oneTimeListeners.containsKey(event) && _oneTimeListeners[event].contains(listener)) {
               _oneTimeListeners[event].remove(listener);
           }
  +
  +        return this;
       }
   
  -    void removeAllListeners([String event]) {
  +    EventEmitter removeAllListeners([String event]) {
           if (event == null) {
               _listeners.clear();
           } else{
  
positive.code:     static int defaultMaxListeners = 10;
      int _maxListeners;
  
      void addListener(String event, Function listener) {
          if (!_listeners.containsKey(event)) {
              _listeners[event] = [];
          }
  
          verifyListenersLimit(event);
  
          _listeners[event].add(listener);
      }
  
      void on(String event, Function listener) {
          addListener(event, listener);
      }
  
      void once(String event, Function listener) {
          if (!_oneTimeListeners.containsKey(event)) {
              _oneTimeListeners[event] = [];
          }
  
          verifyListenersLimit(event);
  
          _oneTimeListeners[event].add(listener);
      }
  
      int _getMaxListeners() {
  
negative.code:         return result;
      }
  
      bool emit(String event) {
          bool handlersFound = false;
  
          if (_listeners.containsKey(event)) {
              handlersFound = true;
              _listeners[event].forEach((Function handler) {
                  handler();
              });
          }
  
          if (_oneTimeListeners.containsKey(event)) {
              handlersFound = true;
              for (int i = 0; i < _oneTimeListeners[event].length; i++) {
                  Function handler = _oneTimeListeners[event][i];
                  handler();
                  _oneTimeListeners[event].removeAt(i);
              }
          }
  
          return handlersFound;
      }
  
      static int listenerCount(EventEmitterInterface emitter, String event) {
  