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This change adds a message bubble to the login screen and
generates a system notification on login for Supervised
Users, both of which indicate that the Supervised User
feature is to be deprecated.

Bug: 899017
Change-Id: I05b684f183a47b6275442caf8e7a4820bda0374e
Reviewed-on: https://chromium-review.googlesource.com/c/1324310
Commit-Queue: Danan S <danan@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Rahul Chaturvedi <rkc@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607373}