class BlockPluginHasSettingsTrayFormAccessCheck

class BlockPluginHasSettingsTrayFormAccessCheck implements AccessInterface {

  /**
   * Checks access for accessing a block's 'settings_tray' form.
   *
   * @param \Drupal\block\BlockInterface $block
   *   The block whose 'settings_tray' form is being accessed.
   *
   * @return \Drupal\Core\Access\AccessResultInterface
   *   The access result.
   */
  public function access(BlockInterface $block) {

    /** @var \Drupal\Core\Block\BlockPluginInterface $block_plugin */
    $block_plugin = $block
      ->getPlugin();
    return $this
      ->accessBlockPlugin($block_plugin);
  }

  /**
   * Checks access for accessing a block plugin's 'settings_tray' form.
   *
   * @param \Drupal\Core\Block\BlockPluginInterface $block_plugin
   *   The block plugin whose 'settings_tray' form is being accessed.
   *
   * @return \Drupal\Core\Access\AccessResultInterface
   *   The access result.
   *
   * @see settings_tray_preprocess_block()
   */
  public function accessBlockPlugin(BlockPluginInterface $block_plugin) {
    return AccessResult::allowedIf($block_plugin instanceof PluginWithFormsInterface && $block_plugin
      ->hasFormClass('settings_tray'));
  }

}