[DL]: Add display_lock OWNERS.

This patch adds OWNERS for display locking.

R=chrishtr@chromium.org, rakina@chromium.org

Change-Id: I694dd98886d25f061e8541f85eea888968e99e9a
Reviewed-on: https://chromium-review.googlesource.com/c/1474330Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632379}

third_party/blink/renderer/core/display_lock/OWNERS

+chrishtr@chromium.org
+rakina@chromium.org
+vmpstr@chromium.org