GitLab

This CL:
* Removes IsRunningInForcedAppMode from ChromeShellDelegate
  (ash.mojom.SessionInfo.is_running_in_app_mode is used instead).
* Moves enabling of MagnifierKeyScroller and SpokenFeedbackToggler
  to ash::Shell.
* Eliminates unused PreShutdown method.
* Replaces call back into ash::Shell (ugh!) to show settings with
  direct call.

Bug: 665064

Change-Id: I31e68366be2f6efab3845be6d00ebc3e967c99c7
Reviewed-on: https://chromium-review.googlesource.com/1070771Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561635}