Move persistent notification id from notification database to profile.

Create a profile field that has the persistent notification ID, where it
can be stored on disk, as this value needs to persist across restarts.

Updating related unit tests.

Bug: 856603
Change-Id: I5c7083c8359c5e7fd7a2b612b861e8968150e90f
Reviewed-on: https://chromium-review.googlesource.com/1114840
Commit-Queue: Sharon Yang <yangsharon@google.com>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575236}
19 files changed