anchor.diff:      _className = style == null ? '': style._className;
       _children = children == null ? _emptyList : children;
   
  -    if (_debugWarnings()) {
  +    if (_isInCheckedMode) {
         _debugReportDuplicateIds();
       }
     }
  
positive.code: 
  abstract class App extends Component {
    sky.Node _host = null;
    App()
      : super(stateful: true) {
  
      _host = sky.document.createElement('div');
      sky.document.appendChild(_host);
  
      new Future.microtask(() {
        Stopwatch sw = new Stopwatch()..start();
        _sync(null, _host, null);
        assert(_root is sky.Node);
        sw.stop();
        print("Initial render: ${sw.elapsedMicroseconds} microseconds");
      });
    }
  }
  
negative.code: 
    _dirtyComponents.clear();
    _renderScheduled = false;
  
    sw.stop();
    if (_shouldLogRenderDuration)
      print("Render took ${sw.elapsedMicroseconds} microseconds");
  }
  
  void _scheduleComponentForRender(Component c) {
  