anchor.diff:    ScrollableMixedWidgetList({
       Key key,
       double initialScrollOffset,
  +    ScrollListener onScroll,
       this.builder,
       this.token,
       this.onInvalidatorAvailable
  -  }) : super(key: key, initialScrollOffset: initialScrollOffset);
  +  }) : super(
  +    key: key,
  +    initialScrollOffset: initialScrollOffset,
  +    onScroll: onScroll
  +  );
   
     final IndexedBuilder builder;
     final Object token;
  
positive.code: 
    void _handleDragEnd(Offset velocity) {
      fling(velocity);
    }
  
    final List<ScrollListener> _listeners = new List<ScrollListener>();
    void addListener(ScrollListener listener) {
      _listeners.add(listener);
    }
  
    void removeListener(ScrollListener listener) {
      _listeners.remove(listener);
    }
  
    void _notifyListeners() {
      List<ScrollListener> localListeners = new List<ScrollListener>.from(_listeners);
      for (ScrollListener listener in localListeners)
        listener();
    }
  }
  
  
negative.code:     key: key,
      initialScrollOffset: initialScrollOffset,
      scrollDirection: scrollDirection,
      onScroll: onScroll,
      itemsWrap: itemsWrap,
      itemExtent: itemExtent,
      padding: padding);
  