code: protected function getToplevelController()
      {
          $c = $this->owner->getController();
          while ($c && $c instanceof GridFieldDetailForm_ItemRequest) {
              $c = $c->getController();
          }
          return $c;
      }
docs: Gets the top level controller.
  
  @return Controller
  @todo  This had to be directly copied from {@link GridFieldDetailForm_ItemRequest}
  because it is a protected method and not visible to a decorator!