anchor.diff:    try {
       _asyncRunCallbackLoop();
     } finally {
  +    _lastPriorityCallback = null;
       _isInCallbackLoop = false;
       if (_nextCallback != null) _AsyncRun._scheduleImmediate(_asyncRunCallback);
     }
  
positive.code:  * It is only used internally to give higher priority to error reporting.
   */
  void _schedulePriorityAsyncCallback(callback) {
    if (_nextCallback == null) {
      _scheduleAsyncCallback(callback);
    } else {
      _AsyncCallbackEntry newEntry = new _AsyncCallbackEntry(callback);
      newEntry.next = _nextCallback;
      _nextCallback = newEntry;
    }
  }
  
  
negative.code: 
  void _asyncRunCallbackLoop() {
    while (_nextCallback != null) {
      _lastPriorityCallback = null;
      _AsyncCallbackEntry entry = _nextCallback;
      _nextCallback = entry.next;
      if (_nextCallback == null) _lastCallback = null;
  