diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 8688704..bf3c9f2 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -1062,13 +1062,16 @@ function menu_tree($menu_name) {
  * - collapsed: The menu item has a submenu which is not shown.
  * - leaf: The menu item has no submenu.
  *
- * @param $tree
+ * @param array $tree
  *   A data structure representing the tree as returned from menu_tree_data.
+ * @param bool $add_active_classes
+ *   (optional) Whether to mark items in the active trail with appriate CSS 
+ *   classes. If turned off, the data is useful for caching.
  *
  * @return
  *   A structured array to be rendered by drupal_render().
  */
-function menu_tree_output($tree, $add_active_classes = TRUE) {
+function menu_tree_output(array $tree, $add_active_classes = TRUE) {
   $build = array();
   $items = array();
 
@@ -1400,6 +1403,10 @@ function menu_tree_page_data($menu_name, $max_depth = NULL, $only_active_trail =
  *   - conditions: An associative array of custom database select query
  *     condition key/value pairs; see _menu_build_tree() for the actual query.
  *
+ *   If neither the 'active_trail', nor the 'only_active_trail' parameters are
+ *   provided, the localized, access filtered menu tree is cached per user. If
+ *   active trail items are marked, reusable caching is not possible.
+ *
  * @return
  *   A fully built menu tree.
  */
@@ -1416,7 +1423,7 @@ function menu_build_tree($menu_name, array $parameters = array()) {
   // If there's no active trail tracking, then add per-user caching of the
   // localized, access-filtered menu subtrees.
   else {
-    global $user;
+    $user = \Drupal::request()->attributes->get('account');
     $language_interface = language(Language::TYPE_INTERFACE);
     $trees = &drupal_static(__FUNCTION__, array());