GitLab

The delegates will become optional in favour of notification handlers,
so simulate events through the NotificationDisplayServiceTester instead.

Bug: 
Change-Id: I501da74ed0691e9bdb89bda139ecb12644a88893
Reviewed-on: https://chromium-review.googlesource.com/806835
Commit-Queue: Peter Beverloo <peter@chromium.org>
Reviewed-by: Anita Woodruff <awdf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521713}