anchor.diff:  const EdgeDims _kTabLabelPadding = const EdgeDims.symmetric(horizontal: 12.0);
   const TextStyle _kTabTextStyle = const TextStyle(textAlign: TextAlign.center);
   const int _kTabIconSize = 24;
  +const double _kTabBarScrollFriction = 0.005;
   
   class TabBarParentData extends BoxParentData with
       ContainerParentDataMixin<RenderBox> { }
  
positive.code:   }
  }
  
  class TabBar extends Scrollable {
    TabBar({
      String key,
  
negative.code:       scrollTo(0.0);
    }
  
    ScrollBehavior createScrollBehavior() => new TabBarScrollBehavior();
    TabBarScrollBehavior get scrollBehavior => super.scrollBehavior;
  
    void _handleTap(int tabIndex) {
      if (tabIndex != selectedIndex && onChanged != null)
  