anchor.diff:    Zone _zone;
   
     int _rafId = 0;
  -  Frame _currentFrame;
  -  Frame _nextFrame;
  +  Frame _currentFrame = new Frame();
  +  Frame _nextFrame = new Frame();
   
     DOMScheduler() {
       _zoneSpec = new ZoneSpecification(scheduleMicrotask: _scheduleMicrotask);
  
positive.code: 
      _zone.run(() {
        _running = true;
        _currentFrame = _nextFrame;
        _nextFrame = null;
        final wq = _currentFrame._writeQueue;
  
        do {
  
negative.code: 
    /// [Frame] that contains tasks for the current animation frame
    Frame get currentFrame {
      assert(_running);
      return _currentFrame;
    }
  
    /// [Frame] that contains tasks for the next animation frame.
    Frame get nextFrame {
      _requestAnimationFrame();
      return _nextFrame;
    }
  
  