anchor.diff:    void clearModel() {
       element.clearModel();
     }
  +
  +  void remove() {
  +    element.remove();
  +  }
   }
   
   main() {
     useHtmlConfiguration();
  +
  +  if (MutationObserver.supported) {
  +    stepDuration = new Duration();
  +  } else {
  +    // Need to step after the tree update notifications, but on IE9 these may
  +    // get polyfilled to use setTimeout(0). So use a longer timer to try to
  +    // get a later callback.
  +    stepDuration = new Duration(milliseconds: 15);
  +  }
   
     test('basic top down', () {
       var a = new DivElement();
  
positive.code: 
        c.clearModel();
        expect(d.model, model2);
      });
    });
  
  
negative.code: import '../../pkg/unittest/lib/unittest.dart';
  import '../../pkg/unittest/lib/html_config.dart';
  
  var stepDuration;
  Future get nextStep {
    return new Future.delayed(stepDuration);
  }
  
  class ModelTracker {
  