anchor.diff:    _WriteGroup _writeGroup;
   
     HeapPriorityQueue<_WriteGroup> _writeQueue =
  -      new HeapPriorityQueue<_WriteGroup>();
  +  new HeapPriorityQueue<_WriteGroup>();
   
     Completer _readCompleter;
     Completer _afterCompleter;
  
positive.code:   }
  
    void run(fn) {
      _zone.run(() {
        flags |= tickRunningFlag;
  
  
negative.code:       return;
      }
  
      time = html.window.performance.now();
  
      _zone.run(() {
        flags &= ~tickPendingFlag;
        flags |= tickRunningFlag;
  