anchor.diff:  
   abstract class BuildContext {
     InheritedWidget inheritedWidgetOfType(Type targetType);
  +  RenderObject findRenderObject();
   }
   
   /// Elements are the instantiations of Widget configurations.
  
positive.code:   /// Pointer to the owner Element object
    StatefulComponentElement _element;
  
    /// Called when this object is inserted into the tree. Override this function
    /// to perform initialization that depends on the location at which this
    /// object was inserted into the tree or on the widget configuration object.
  
negative.code:       ancestor = ancestor._parent;
      return ancestor?.widget;
    }
  
    RenderObject findRenderObject() => renderObject;
  
    void dependenciesChanged() {
      assert(false);
  