GitLab

This CL also adds the system notification warning level as a field in
Notification.

BUG=1073726

Change-Id: I7e432f362fc6269e3fe06c671bfca0588850f539
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2200630
Commit-Queue: Tim Song <tengs@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771228}