diff --git a/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php b/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php
index 539a8c1..173b051 100644
--- a/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php
+++ b/core/modules/block/lib/Drupal/block/Controller/BlockAutocompleteController.php
@@ -75,4 +75,18 @@ public function autocomplete(Request $request) {
     return new JsonResponse($matches);
   }
 
+  /**
+   * Sets whether the admin menu is in compact mode or not.
+   *
+   * @param string $mode
+   *   Valid values are 'on' and 'off'.
+   *
+   * @return \Symfony\Component\HttpFoundation\RedirectResponse
+   *   A redirect response. Redirects back to the front page.
+   */
+  public function compactPage($mode) {
+    user_cookie_save(array('admin_compact_mode' => ($mode == 'on')));
+    return new RedirectResponse(url('<front>', array('absolute' => TRUE)));
+  }
+
 }