anchor.diff:      Key key,
       this.tag,
       this.child,
  -    this.turns: 1
  +    this.turns: 1,
  +    this.alwaysAnimate: false
     }) : super(key: key) {
       assert(tag != null);
     }
  
positive.code:   final Object tag;
    final Widget child;
    final int turns;
  
    static Map<Object, HeroHandle> of(BuildContext context, Set<Key> mostValuableKeys) {
      mostValuableKeys ??= new Set<Key>();
  
negative.code: }
  
  abstract class HeroHandle {
    bool get alwaysAnimate;
    _HeroManifest _takeChild(Rect animationArea);
  }
  
  