GitLab

-New public method for checking users in UsersPrivate API

-Add a new private method just for checking if a user is part of the
user list since two methods need the same functionality.

-New test includes a negative test for not finding a user + a positive
test after a user is added and searched for.

Bug: 768798
Change-Id: I8ec2ca524549fbd8dd9a0813a7bf7777fe7ed2d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1786862
Commit-Queue: Gavin Williams <gavinwill@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699586}