anchor.diff:    final AnimatedRelativeRectValue currentRect;
     final AnimatedValue<double> currentTurns;
   
  +  bool get alwaysAnimate => true;
  +
     bool get taken => _taken;
     bool _taken = false;
     _HeroManifest _takeChild(Rect animationArea) {
  
positive.code: }
  
  abstract class HeroHandle {
    _HeroManifest _takeChild(Rect animationArea);
  }
  
  
negative.code:     Key key,
      this.tag,
      this.child,
      this.turns: 1,
      this.alwaysAnimate: false
    }) : super(key: key) {
      assert(tag != null);
    }
  