GitLab

Match the rule used in other Google open source projects described
at https://opensource.google/docs/thirdparty/documentation/#owners:
the first lines in the OWNERS file are

* Two committers, OR
* A file: directive pointing to another OWNERS file in //third_party

(Copied by jrn@ from an internal CL making the same change; fleshed
out the commit message.)

Change-Id: I4e031684941e90a5d9257d053ca0d36d7da6f67f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2276813Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#784225}