AppListController refactoring part 3: Switching over to use AppListShower in Ash.

Part 1 of the refactoring: https://crrev.com/1830293002
Part 2 of the refactoring: https://crrev.com/1856943003
Design doc: https://docs.google.com/document/d/1M9vqTTuprMssRXs8UIVaFjQUq3lUxSzwrWoPjPvca6Q/edit?ts=56d0e9f0#heading=h.b2znwtuxd2x2

This CL makes Ash use app_list::AppListShowerImpl + ash::AppListShowerDelegate
tandem instead of ash::AppListController. AppListShower is owned by
AppListServiceAsh, and Ash goes to AppListServiceAsh (through
ChromeShellDelegate) when it needs to hide or show the app list.

BUG=557408

Review URL: https://codereview.chromium.org/1861013004

Cr-Commit-Position: refs/heads/master@{#386136}
32 files changed