anchor.diff:  /// * [ClampingScrollPhysics], which is the analogous physics for Android's
   ///   clamping behavior.
   class BouncingScrollPhysics extends ScrollPhysics {
  +  /// Creates scroll physics that bounce back from the edge.
     const BouncingScrollPhysics({ ScrollPhysics parent }) : super(parent);
   
     @override
  
positive.code: ///   provide the glowing effect that is usually found with this clamping effect
  ///   on Android.
  class ClampingScrollPhysics extends ScrollPhysics {
    const ClampingScrollPhysics({ ScrollPhysics parent }) : super(parent);
  
    @override
  
negative.code: /// * [ClampingScrollPhysics], which provides the clamping overscroll behavior
  ///   found on Android.
  class AlwaysScrollableScrollPhysics extends ScrollPhysics {
    /// Creates scroll physics that always lets the user scroll.
    const AlwaysScrollableScrollPhysics({ ScrollPhysics parent }) : super(parent);
  
    @override
  