Make PlatformNotificationContext display all notifications.

This hands off the display call to PlatformNotificationContext which
gets rid of some code duplication as we always want to show a
notification after writing it into the NotificationDatabase.

Bug: 891339
Change-Id: If0787fcd9668cb0e419edcc16a56c91649983dcc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1511416
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Richard Knoll <knollr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#643370}
7 files changed