anchor.diff:      PointerEventListener onPointerDown,
       PointerEventListener onPointerMove,
       PointerEventListener onPointerUp,
  -    Map<String, sky.EventListener> custom
  +    Map<String, EventListener> custom
     }) {
       var listeners = custom != null ?
  -        new HashMap<String, sky.EventListener>.from(custom) :
  -        new HashMap<String, sky.EventListener>();
  +        new HashMap<String, EventListener>.from(custom) :
  +        new HashMap<String, EventListener>();
   
       if (onWheel != null)
         listeners['wheel'] = onWheel;
  
positive.code:     PointerEventListener onPointerDown,
      PointerEventListener onPointerMove,
      PointerEventListener onPointerUp,
      Map<String, sky.EventListener> custom
    }) : listeners = _createListeners(
           onWheel: onWheel,
           onGestureFlingCancel: onGestureFlingCancel,
  
negative.code:   }
  
    void _handleEvent(sky.Event e) {
      EventListener listener = listeners[e.type];
      if (listener != null) {
        listener(e);
      }
  