Migrate the push tests to the NotificationDisplayServiceTester

BUG=

Change-Id: Ibf85048b885e394a8f078fb5903d1863f0357420
Reviewed-on: https://chromium-review.googlesource.com/613720
Commit-Queue: Peter Beverloo <[email protected]>
Reviewed-by: John Mellor <[email protected]>
Cr-Commit-Position: refs/heads/master@{#496750}
7 files changed