GitLab

Add empty alt to the extension's image
because the name of the extension is presented.
Add backButton alt to be consistent with other Settings pages.
Cover all the issues by tests.

Bug: 879146
Change-Id: I74d4c8683fac4b9051eb43706b260fe0e030a5c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1554769
Commit-Queue: Roman Aleksandrov <raleksandrov@google.com>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#650513}