To fix a shutdown crash in which signin_screen_handler was removing itself from observing lock_screen_apps::StateController (issue 739596), https://chromium-review.googlesource.com/c/560648 is adding a two step destruction to lock_screen_apps::StateController (Shutdown method that is called before profiles shutdown; the StateController object is destruction is delayed until ChromeBrowserMainChromeOS goes out of scope).

When SigninScreenHandler usage in lock screen goes away, this approach should be revisited - it might be possible to remove Shutdown method, and replace it with lock_screen_apps::StateController instance destruction.