anchor.diff:  
   final List<UINode> _emptyList = new List<UINode>();
   
  -abstract class WrapperNode extends RenderNode {
  +abstract class SkyElementWrapper extends SkyNodeWrapper {
   
     String get _tagName;
   
  
positive.code:   }
  
    static void _dispatchEvent(sky.Event e) {
      UINode target = RenderNode._getMounted(e.target);
  
      // TODO(rafaelw): StopPropagation?
      while (target != null) {
  
negative.code: 
    static final Text _emptyText = new Text(null);
  
    SkyNodeWrapper get _emptyNode => _emptyText;
  
    sky.Node _createNode() {
      return new sky.Text(data);
    }
  
    void _syncNode(SkyNodeWrapper old) {
      if (old == _emptyText)
        return; // we set inside _createNode();
  
  