Add a test for Notification.permission.

This CL adds an interactive UI test for the
window.Notification.permission API. In particular, it checks that the
correct value is returned when the notifications permission has been
embargoed due to multiple dismissals.

BUG=730273

Review-Url: https://codereview.chromium.org/2925203003
Cr-Commit-Position: refs/heads/master@{#477920}
4 files changed