I'll take over this bug since I have been working with the TestBase classes a lot (and will be for the near future).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f005a0352a04da2ddc613e28e7500524c48da65a

commit f005a0352a04da2ddc613e28e7500524c48da65a
Author: Quan Nguyen <qnnguyen@chromium.org>
Date: Mon Nov 19 18:39:15 2018

cros: Move non-keyboard functionality out of LoginKeyboardTestBase

As part of this CL, we move LockScreen control and user account functions into
LoginTestBase and make LoginKeyboardTestBase a subclass. In the future, test
fixtures with new login-related functionality can inherit from LoginTestBase.

Bug:  809330 
Change-Id: I0d082a60e667fec7fd391984de6469ead5d57e77
Reviewed-on: https://chromium-review.googlesource.com/c/1338476
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609363}
[modify] https://crrev.com/f005a0352a04da2ddc613e28e7500524c48da65a/ash/login/ui/lock_contents_view_unittest.cc
[modify] https://crrev.com/f005a0352a04da2ddc613e28e7500524c48da65a/ash/login/ui/lock_window_unittest.cc
[modify] https://crrev.com/f005a0352a04da2ddc613e28e7500524c48da65a/ash/login/ui/login_keyboard_test_base.cc
[modify] https://crrev.com/f005a0352a04da2ddc613e28e7500524c48da65a/ash/login/ui/login_keyboard_test_base.h
[modify] https://crrev.com/f005a0352a04da2ddc613e28e7500524c48da65a/ash/login/ui/login_test_base.cc
[modify] https://crrev.com/f005a0352a04da2ddc613e28e7500524c48da65a/ash/login/ui/login_test_base.h