GitLab

When a sync user confirms to sign out after trying to turn
off the signin-allowed toggle, the toggle is now turned off.

Additional change:
 - The code related to the sign-out dialog in settings is
 extracted into its own element and refactored.

Bug: 892745
Change-Id: I9d638d8c77b1f4318fc592cc88f4be95e5eab7c8
Reviewed-on: https://chromium-review.googlesource.com/c/1280542Reviewed-by: Scott Chen <scottchen@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600997}