Issue #767404 by das-peter, geru, Ketan Harit, nikhilsukul, Nitesh Sethia: theme_menu_tree() removes helpful data for theming custom menu trees

CHANGELOG.txt

@@ -4,6 +4,7 @@ Drupal 7.54, xxxx-xx-xx (development version)
 - Modules are now able to define theme engines.
 - Numerous bug fixes.
 - Logging of searches can now be disabled.
+- Added menu tree render structure to (pre-)process hooks for theme_menu_tree().
 
 Drupal 7.53, 2016-12-07
 -----------------------

includes/menu.inc

@@ -1606,6 +1606,7 @@ function _menu_tree_data(&$links, $parents, $depth) {
  * Implements template_preprocess_HOOK() for theme_menu_tree().
  */
 function template_preprocess_menu_tree(&$variables) {
+  $variables['#tree'] = $variables['tree'];
   $variables['tree'] = $variables['tree']['#children'];
 }