anchor.diff:      if (ourEvent is PointerInputEvent) {
         _handlePointerInputEvent(ourEvent);
       } else {
  +      assert(event.type == 'back');
         for (EventListener listener in _eventListeners)
           listener(ourEvent);
       }
  
positive.code:   }
    return weight;
  }
  
  typedef void EventListener(InputEvent event);
  
  /// A hit test entry used by [FlutterBinding]
  class BindingHitTestEntry extends HitTestEntry {
  
negative.code:   RenderView get renderView => _renderView;
    RenderView _renderView;
  
    final List<MetricListener> _metricListeners = new List<MetricListener>();
  
    /// Calls listener for every event that isn't localized to a given view coordinate
    void addMetricListener(MetricListener listener) => _metricListeners.add(listener);
  
    /// Stops calling listener for every event that isn't localized to a given view coordinate
    bool removeMetricListener(MetricListener listener) => _metricListeners.remove(listener);
  
    void _handleMetricsChanged() {
      Size size = new Size(ui.view.width, ui.view.height);
      _renderView.rootConstraints = new ViewConstraints(size: size);
      for (MetricListener listener in _metricListeners)
        listener(size);
    }
  
    /// Pump the rendering pipeline to generate a frame for the given time stamp
  