Push API: Forced notifications should use Notifications database

1. Writes to the Notifications database when creating forced notifications.

2. Uses Notifications database when counting notifications, instead of the unreliable NotificationUIManager APIs.

This gives more reliable values after browser restarts.

BUG=437277
TBR=avi@chromium.org

Review URL: https://codereview.chromium.org/1099093003

Cr-Commit-Position: refs/heads/master@{#327716}
4 files changed