GitLab

This CL adds a new observer method for that.
We don't really need the OnManagerGoingDown() method since the coordinator
can live longer

BUG=942770

Change-Id: Ieaf3e13facc52022f2ec35c8cdf0f3a7c0170fd5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1546259
Commit-Queue: Min Qin <qinmin@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646565}