GitLab

In notification settings, there was no defualt icon for notifier
without favicon. As a result, the notifier texts are not aligend.

Before: http://screen/Dm5RpJ42F98
After: http://screen/0tx8h9G9GPb

TEST=manual
BUG=768736

Change-Id: Id0e1ebc674c39acac63036bee7d1fa91f0817e86
Reviewed-on: https://chromium-review.googlesource.com/686086Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504861}