anchor.diff:      currentNode = null;
       while (oldStartIndex < oldEndIndex) {
         oldNode = oldChildren[oldStartIndex];
  -      oldNode._remove();
  +      _removeChild(oldNode);
         advanceOldStartIndex();
       }
     }
  
positive.code: 
  final bool _isInCheckedMode = _initIsInCheckedMode();
  final bool _shouldLogRenderDuration = false;
  
  class Style {
    final String _className;
  
negative.code:     _root = null;
    }
  
    void _ensureDepth() {
      if (_nodeDepth == null) {
        _nodeDepth = 0;
        Node parent = _parent;
        while (parent != null) {
          _nodeDepth++;
          parent = parent._parent;
        }
      }
    }
  
    void _trace(String message) {
      if (!_shouldTrace)
        return;
  
      _ensureDepth();
      StringBuffer buffer = new StringBuffer();
      int depth = _nodeDepth;
      while (depth-- > 0) {
        buffer.write(' ');
      }
      buffer.write(message);
      print(buffer);
    }
  
    void _removeChild(Node node) {
      _trace('_sync(remove) ${node._key}');
      node._remove();
    }
  
    // Returns the child which should be retained as the child of this node.
    Node _syncChild(Node node, Node oldNode, sky.ParentNode host,
        sky.Node insertBefore) {
  
      if (node == oldNode) {
        _trace('_sync(identical) ${node._key}');
        return node; // Nothing to do. Subtrees must be identical.
      }
  
      // TODO(rafaelw): This eagerly removes the old DOM. It may be that a
      // new component was built that could re-use some of it. Consider
      // syncing the new VDOM against the old one.
      if (oldNode != null && node._key != oldNode._key) {
        _trace('_sync(remove) ${node._key}');
        oldNode._remove();
      }
  
      if (node._willSync(oldNode)) {
        _trace('_sync(statefull) ${node._key} -> ${oldNode._key}');
        oldNode._sync(node, host, insertBefore);
        node._defunct = true;
        assert(oldNode._root is sky.Node);
  