anchor.diff:      this.leadingController,
       this.trailingController,
       this.axisDirection,
  +    Listenable repaint,
     }) : super(
  -    repaint: new Listenable.merge(<Listenable>[leadingController, trailingController])
  +    repaint: repaint,
     );
   
     /// The controller for the overscroll glow on the side with negative scroll offsets.
  
positive.code: class _GlowingOverscrollIndicatorState extends State<GlowingOverscrollIndicator> with TickerProviderStateMixin {
    _GlowController _leadingController;
    _GlowController _trailingController;
  
    @override
    void initState() {
      super.initState();
      _leadingController = new _GlowController(vsync: this, color: widget.color, axis: widget.axis);
      _trailingController = new _GlowController(vsync: this, color: widget.color, axis: widget.axis);
    }
  
    @override
  
negative.code:             leadingController: widget.showLeading ? _leadingController : null,
              trailingController: widget.showTrailing ? _trailingController : null,
              axisDirection: widget.axisDirection,
              repaint: _leadingAndTrailingListener,
            ),
            child: new RepaintBoundary(
              child: widget.child,
  