Notifications: Allow removing non-visible notifications in MessageCenter.

Currently, MessageCenter::RemoveNotification() only removes "visible"
notifications. In multi-user mode (and other scenarios), notifications for
non-active users are blocked and not "visible".

When Android dismisses an ARC notification from a non-active user, the
corresponding MessageCenter notification is not properly removed. Accessing the
invalid notification will result in a crash.

BUG=940060
TEST=new unit test, verified bug does not repro

Change-Id: Ic6688b4d7137777d7b77dc07a823681927975dc8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1530476
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tim Song <tengs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641913}
3 files changed