anchor.diff:  
     OutlineTopLevelItem _addItem(OutlineTopLevelItem item) {
       _rootList.append(item.element);
  -    _outlineItems.add(item);
       item.onClick.listen((event) => _childSelectedController.add(item));
       return item;
     }
  
positive.code:     if (members.length > 0) {
        _offsetRange.bottom = members[0]._offsetRange.top - 1;
      }
      // Constructor's offsetRange.
      for (int i = 0; i < members.length; ++i) {
        OutlineItem member = members[i];
        if (member._data.name == _data.name) {
          if (i > 0) {
            member._offsetRange.top = members[i - 1]._offsetRange.bottom + 1;
          }
  
negative.code:       _create(data);
      }
  
      if (_lastScrolledOffsetRange != null) {
        scrollPosition = _lastScrolledOffsetRange;
      }
    }
  
    OutlineTopLevelItem _create(services.OutlineTopLevelEntry data) {
  