[Extensions] Update notification system observer test to use manifest v2

Update notification_system_observer_unittest.cc to generate
extensions with manifest_version 2.

Bug: 816679
Change-Id: Ida57ff94738d3ec7fcfb207b8495d7a31d784a94
Reviewed-on: https://chromium-review.googlesource.com/1008607
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549990}
1 file changed