Maintenance for Chrome race condition. See Bug 61504 for description

The root issue is that the back button is available before the notifications
page manifests and the test clicks it, so that while Chrome displays the
notification page, the URL Chrome shows is actually already back on Watchlist.
This seems unlikely to affect a user.

Change-Id: I27859d4ab1850f8b4ebc0d4c10f1e54180f33cd3
Merge "Maintenance for Chrome race condition. See Bug 61504 for description"