class BlockListController

class BlockListController extends EntityListController {

  /**
   * The theme handler.
   *
   * @var \Drupal\Core\Extension\ThemeHandlerInterface
   */
  protected $themeHandler;

  /**
   * Constructs the BlockListController.
   *
   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
   *   The theme handler.
   */
  public function __construct(ThemeHandlerInterface $theme_handler) {
    $this->themeHandler = $theme_handler;
  }

  /**
   * Shows the block administration page.
   *
   * @param string|null $theme
   *   Theme key of block list.
   * @param \Symfony\Component\HttpFoundation\Request $request
   *   The current request.
   *
   * @return array
   *   A render array as expected by
   *   \Drupal\Core\Render\RendererInterface::render().
   */
  public function listing($theme = NULL, Request $request = NULL) {
    $theme = $theme ?: $this
      ->config('system.theme')
      ->get('default');
    if (!$this->themeHandler
      ->hasUi($theme)) {
      throw new NotFoundHttpException();
    }
    return $this
      ->entityTypeManager()
      ->getListBuilder('block')
      ->render($theme, $request);
  }

}