anchor.diff:    }
   
     Duration get transitionDuration;
  -
  -  bool get isActuallyOpaque => (performance == null || _performance.isCompleted) && opaque;
   
     Widget build(NavigatorState navigator, PerformanceView nextRoutePerformance);
   
  
positive.code:   }
  
    void _handlePerformanceStatusChanged(PerformanceStatus status) {
      if (status == PerformanceStatus.dismissed) {
        _navigator._didDismissRoute(this);
        _navigator._removeRoute(this);
        _navigator = null;
  
negative.code:   bool _debugCurrentlyHaveRoute(Route route) {
      int index = _history.indexOf(route);
      return index >= 0 && index <= _currentPosition;
    }
  
    void _didCompleteRoute(Route route) {
      assert(_history.contains(route));
      if (route.isActuallyOpaque) {
        setState(() {
          // we need to rebuild because our build function depends on
          // whether the route is opaque or not.
        });
      }
    }
  
    void _didDismissRoute(Route route) {
  