anchor.diff:              leadingController: widget.showLeading ? _leadingController : null,
               trailingController: widget.showTrailing ? _trailingController : null,
               axisDirection: widget.axisDirection,
  +            repaint: _leadingAndTrailingListener,
             ),
             child: new RepaintBoundary(
               child: widget.child,
  
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: 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
  