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