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(c.models, [model, cModel, model]);
        expect(d.models, [model, cModel, model]);
      });
    });
  
  
negative.code:       expect(b.models, [aModel]);
        expect(c.models, [cModel]);
        expect(d.models, [cModel]);
  
        a.remove();
        return nextStep;
      });
    });
  }
  