anchor.diff:      final Performance performance = _selection.performance;
   
       if (performance.status == PerformanceStatus.completed) {
  -      _initItemsAndScrollOffset();
  +      _updateItemsAndScrollBehavior();
         return;
       }
   
  
positive.code:     _initSelection(TabBarSelection.of(context));
    }
  
    void dispose() {
      _selection?.unregisterPerformanceListener(this);
      super.dispose();
  
negative.code:     _selection = selection;
      if (_selection != null) {
        _selection.registerPerformanceListener(this);
        _updateItemsAndScrollBehavior();
      }
    }
  
  