anchor.diff:  
     void _fireResourceEvent(ResourceChangeEvent event) => _resourceController.add(event);
   
  -  void _fireMarkerEvent(MarkerChangeEvent event) {
  +  void _fireMarkerEvent(List<MarkerDelta> deltas) {
       if (_markersPauseCount == 0) {
  -      _markerController.add(event);
  +      _markerController.add(new MarkerChangeEvent.fromList(deltas));
       } else {
  -      _makerChangeList.addAll(event.changes);
  +      _makerChangeList.addAll(deltas);
       }
     }
   
  
positive.code: 
    void _fireResourceEvent(ResourceChangeEvent event) => _parent._fireResourceEvent(event);
  
    void _fireMarkerEvent(MarkerChangeEvent event) => _parent._fireMarkerEvent(event);
  
    Future delete();
  
  
negative.code:   void _clearMarkers({bool fireEvent : true}) {
      _markers.clear();
      if (fireEvent) {
        _fireMarkerEvent([new MarkerDelta(this, null, EventType.DELETE)]);
      }
    }
  
  