anchor.diff:      new Future.microtask(() {
         Stopwatch sw = new Stopwatch()..start();
   
  -      _mount(null, _host, null);
  +      _sync(null, _host, null);
         assert(_root is sky.Node);
   
         sw.stop();
  
positive.code: 
    static final Container _emptyContainer = new Container();
  
    Node get _emptyNode => _emptyContainer;
  
    Container({
      Object key,
  
negative.code: 
      if (height != oldImage.height)
        skyImage.style['height'] = '${height}px';
    }
  }
  
  