Add missing refs.cfg. This is necessary for CQ/Luci operation. Bug: 833848 Change-Id: Ib42216d3a2ee58e819f42fc9535fa91797f55200 Reviewed-on: https://chromium-review.googlesource.com/c/1332529 Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>