Add chromeos/SECURITY_OWNERS to chromeos/lacros/mojom/OWNERS

This is consistent with what we do for ARC++ mojom APIs and should help
spread the review load a bit.

Bug: none
Change-Id: I984838644b64c371b040cf355e3ddcdb83c6b210
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2264795
Auto-Submit: James Cook <jamescook@chromium.org>
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781929}

chromeos/lacros/mojom/OWNERS

-# For Lacros-related changes only. Otherwise use //ipc/SECURITY_OWNERS
-jorgelo@chromium.org
-
 per-file *.mojom=set noparent
 per-file *.mojom=file://ipc/SECURITY_OWNERS
+
+# Prefer Chrome OS owners for large changes to the Lacros API.
+per-file *.mojom=file://chromeos/SECURITY_OWNERS