Add antrim/rsorokin as login UI owners

Change-Id: I8e9a9d7b17368976d6521d4a8891326b8080ec9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1646789
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Commit-Queue: Denis Kuznetsov <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667059}