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This CL fixes the check for the message center being visible.
Also adding a unit test to cover the case that caused the crash.

Change-Id: I37b82b4d3cd08c6c8823dab0b7ddd9342a3c7673
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1857378Reviewed-by: Tim Song <tengs@chromium.org>
Commit-Queue: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705620}