anchor.diff:        return;
   
       _ensureDepth();
  -    StringBuffer buffer = new StringBuffer();
  -    int depth = _nodeDepth;
  -    while (depth-- > 0) {
  -      buffer.write(' ');
  -    }
  -    buffer.write(message);
  -    print(buffer);
  +    print((' ' * _nodeDepth) + message);
     }
   
     void _traceSync(_SyncOperation op, String key) {
  
positive.code:     _root = null;
    }
  
    void _ensureDepth() {
      if (_nodeDepth == null) {
        _nodeDepth = 0;
        UINode parent = _parent;
        while (parent != null) {
          _nodeDepth++;
          parent = parent._parent;
        }
      }
    }
  
  
negative.code:   UINode _parent;
    sky.Node _root;
    bool _defunct = false;
  
    UINode({ Object key }) {
      _key = key == null ? "$runtimeType" : "$runtimeType-$key";
  