anchor.diff:      int len = _list.length;
   
       _notifyChangeLength(len, len - rangeLength);
  -    if (_hasListObservers && rangeLength > 0) {
  +    if (hasListObservers && rangeLength > 0) {
         _recordChange(new ListChangeRecord(this, start,
             removed: _list.getRange(start, end).toList()));
       }
  
positive.code:     return _listChanges.stream;
    }
  
    bool get _hasListObservers =>
        _listChanges != null && _listChanges.hasListener;
  
    @reflectable int get length => _list.length;
  
negative.code: 
      // Produce notifications if needed
      _notifyChangeLength(len, value);
      if (hasListObservers) {
        if (value < len) {
          _recordChange(new ListChangeRecord(this, value,
              removed: _list.getRange(value, len).toList()));
  