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: 
  import 'dart:math' as math;
  
  import 'package:sky/animation/generators.dart';
  import 'package:sky/animation/mechanics.dart';
  import 'package:sky/animation/scroll_behavior.dart';
  import 'package:sky/painting/text_style.dart';
  import 'package:sky/rendering/box.dart';
  