step 4: taking out accidental newlines that were added in menu_ui.module.
Step 4: addressing tim's feedback that we dont do the pattern of having abstract methods, from comment 71
Part 4: clean up. dont need third person verb in return description.
Step 4: use was added. add it in alpha order.
Part 4: mostly in tests, took out accidental new newlines, period at end of sentences, wrapped to 80 chars, new uses in alpha order, added type hint for a constructor
Part 4: clean up docs changed/added in toolbar.module.
Part 4: more little clean up, wrap to 80 chars, fixed an incorrect class name in construct doc, whitespace.
fix caching bug of menus
flag route ad admin
START PART 5: https://www.drupal.org/node/2301319
apply patch https://www.drupal.org/files/issues/menu-2256521-remove-dead-code.patch
and resolve conflicts with 8.x
remove unused constant MENU_MAX_DEPTH