Supervised users a11y test

BUG=315846
R=nkostylev@chromium.org
NOTRY=true
Setting notry to true as win_rel is flaky, and this change is chromeos-specific.
It passes all other bots.

Review URL: https://codereview.chromium.org/83653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237337 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237337