anchor.diff:    static const int lowestPriority = (1 << 31) - 1;
   
     /// Write groups indexed by priority
  -  List<_WriteGroup> _writeGroups = [];
  -  _WriteGroup _lowestPriorityWriteGroup;
  +  List<_WriteGroup> _prioWriteGroups = [];
  +  _WriteGroup _writeGroup;
   
     HeapPriorityQueue<_WriteGroup> _writeQueue =
         new HeapPriorityQueue<_WriteGroup>();
  
positive.code:     return _nextFrame;
    }
  
    void _scheduleMicrotask(Zone self, ZoneDelegate parent, Zone zone, void f()) {
      if (_running) {
        _currentTasks.add(f);
      } else {
        parent.scheduleMicrotask(zone, f);
  
negative.code:   }
  }
  
  /// [Scheduler].
  class Scheduler {
    static const int runningFlag = 1;
    static const int tickPendingFlag = 1 << 1;
    static const int framePendingFlag = 1 << 2;
  
    int flags = 0;
    int clock = 0;
  
    bool get isRunning => ((flags & runningFlag) != 0);
  
    Queue<Function> _currentTasks = new Queue<Function>();
  
    ZoneSpecification _zoneSpec;
    Zone _zone;
  
    /// Scheduler [Zone].
    Zone get zone => _zone;
  
    Frame _currentFrame = new Frame();
    Frame _nextFrame = new Frame();
  
    Completer _nextTickCompleter;
  
    /// [Frame] that contains tasks for the current animation frame.
    Frame get currentFrame {
      assert(isRunning);
      return _currentFrame;
    }
  
  