[Merge to M58] CrOS: Do not allow notifications to be added during shutdown.

[Merge to M58] CrOS: Do not allow notifications to be added during shutdown.

Attempt to fix crash in the bug. I think the cause of this is a notification being added after the shutdown process has started. Somewhat confirmed this by sending a notification after shutdown.

BUG=660962
TEST=unit_tests --gtest_filter="MessageCenterNotificationManagerTest.AddNotificationOnShutdown"

Review-Url: https://codereview.chromium.org/2776933006
Cr-Commit-Position: refs/heads/master@{#460789}
(cherry picked from commit ee04538066ee663d06c4d502435cbad08106a816)

Review-Url: https://codereview.chromium.org/2860473002 .
Cr-Commit-Position: refs/branch-heads/3029@{#790}
Cr-Branched-From: 939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed: https://chromium.googlesource.com/chromium/src/+/8b8080a8da42c9a530d4baddfad2ccb5127b52af

[sammiequon, 2017-05-02 17:11:58]

Description was changed from

==========
[Merge to M58] CrOS: Do not allow notifications to be added during shutdown.

Attempt to fix crash in the bug. I think the cause of this is a notification
being added after the shutdown process has started. Somewhat confirmed this by
sending a notification after shutdown.

BUG=660962
TEST=unit_tests
--gtest_filter="MessageCenterNotificationManagerTest.AddNotificationOnShutdown"

Review-Url: https://codereview.chromium.org/2776933006
Cr-Commit-Position: refs/heads/master@{#460789}
(cherry picked from commit ee04538066ee663d06c4d502435cbad08106a816)
==========

to

==========
[Merge to M58] CrOS: Do not allow notifications to be added during shutdown.

Attempt to fix crash in the bug. I think the cause of this is a notification
being added after the shutdown process has started. Somewhat confirmed this by
sending a notification after shutdown.

BUG=660962
TEST=unit_tests
--gtest_filter="MessageCenterNotificationManagerTest.AddNotificationOnShutdown"

Review-Url: https://codereview.chromium.org/2776933006
Cr-Commit-Position: refs/heads/master@{#460789}
(cherry picked from commit ee04538066ee663d06c4d502435cbad08106a816)

Review-Url: https://codereview.chromium.org/2860473002 .
Cr-Commit-Position: refs/branch-heads/3029@{#790}
Cr-Branched-From:
939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed:
https://chromium.googlesource.com/chromium/src/+/8b8080a8da42c9a530d4baddfad2...
==========

[sammiequon, 2017-05-02 17:11:59]

Committed patchset #1 (id:1) manually as
8b8080a8da42c9a530d4baddfad2ccb5127b52af.