anchor.diff:    void clearMarkers() {
       traverse().where((r) => r.isFile)
           .forEach((f) => (f as File)._clearMarkers(fireEvent : false));
  -    _fireMarkerEvent(new MarkerChangeEvent.fromSingle(new MarkerDelta(this, null,EventType.DELETE)));
  +    _fireMarkerEvent([new MarkerDelta(this, null,EventType.DELETE)]);
     }
   
     int findMaxProblemSeverity(String type) {
  
positive.code:     Marker marker = new Marker(
          this, type, severity, message, lineNum, charStart, charEnd);
      _markers.add(marker);
      _fireMarkerEvent(new MarkerChangeEvent.fromSingle(new MarkerDelta(this, marker, EventType.ADD)));
      return marker;
    }
  
  
negative.code: 
    void _fireResourceEvent(ResourceChangeEvent event) => _parent._fireResourceEvent(event);
  
    void _fireMarkerEvent(List<MarkerDelta> delta) => _parent._fireMarkerEvent(delta);
  
    Future delete();
  
  