gistfile1.php

  foreach (drupal_container()->get('plugin.manager.system.plugin_ui')->getDefinitions() as $plugin_id => $plugin) {
    list($plugin_base, $key) = explode(':', $plugin_id);
    if ($plugin_base == 'block_plugin_ui') {
      $theme = $themes[$key];
      $items['admin/structure/block/list/' . $plugin_id] = array(
        'title' => check_plain($theme->info['name']),
        'page arguments' => array($key),
        'type' => $key == $default_theme ? MENU_DEFAULT_LOCAL_TASK : MENU_LOCAL_TASK,
        'access callback' => '_block_themes_access',
        'access arguments' => array($key),
        'file' => 'block.admin.inc',
      );
      $items['admin/structure/block/demo/' . $key] = array(
        'title' => check_plain($theme->info['name']),
        'page callback' => 'block_admin_demo',
        'page arguments' => array($key),
        'type' => MENU_CALLBACK,
        'access callback' => '_block_themes_access',
        'access arguments' => array($key),
        'theme callback' => '_block_custom_theme',
        'theme arguments' => array($key),
        'file' => 'block.admin.inc',
      );
    }
  }