GitLab

This will be tested by a Chromium browsertest. Service Worker plumbing that would make this possible to test in Blink isn't fitted yet.

BUG=356021

Review URL: https://codereview.chromium.org/214413004

git-svn-id: svn://svn.chromium.org/blink/trunk@170310 bbb929c8-8fbe-4397-9dbb-9b2b20218538