anchor.diff:        renderView = new RenderView();
         renderView.scheduleInitialFrame();
       }
  -    handleMetricsChanged(); // configures _renderView's metrics
  +    handleMetricsChanged(); // configures renderView's metrics
     }
   
     /// The render tree that's attached to the output surface.
     RenderView get renderView => _renderView;
     RenderView _renderView;
     void set renderView(RenderView value) {
  +    assert(value != null);
       if (_renderView == value)
         return;
       if (_renderView != null)
         _renderView.detach();
       _renderView = value;
  -    if (_renderView != null)
  -      _renderView.attach();
  +    _renderView.attach();
     }
   
     void handleMetricsChanged() {
  -    _renderView.rootConstraints = new ViewConstraints(size: ui.window.size);
  +    assert(renderView != null);
  +    renderView.rootConstraints = new ViewConstraints(size: ui.window.size);
     }
   
     void _handlePersistentFrameCallback(Duration timeStamp) {
  
positive.code: 
    /// Pump the rendering pipeline to generate a frame.
    void beginFrame() {
      RenderObject.flushLayout();
      _renderView.updateCompositingBits();
      RenderObject.flushPaint();
      _renderView.compositeFrame();
    }
  
    void hitTest(HitTestResult result, Point position) {
      _renderView.hitTest(result, position: position);
      super.hitTest(result, position);
    }
  }
  
  /// Prints a textual representation of the entire render tree.
  void debugDumpRenderTree() {
    debugPrint(Renderer.instance.renderView.toStringDeep());
  }
  
  /// Prints a textual representation of the entire layer tree.
  void debugDumpLayerTree() {
    debugPrint(Renderer.instance.renderView.layer.toStringDeep());
  }
  
  /// A concrete binding for applications that use the Rendering framework
  /// directly. This is the glue that binds the framework to the Flutter engine.
  class RenderingFlutterBinding extends BindingBase with Scheduler, Renderer, Gesturer {
    RenderingFlutterBinding({ RenderBox root }) {
      renderView.child = root;
    }
  }
  
negative.code:     _instance = this;
      ui.window.onMetricsChanged = handleMetricsChanged;
      initRenderView();
      assert(renderView != null);
      assert(() {
        initServiceExtensions();
        return true;
  