system_api: Add DBus constants and protos for OOBE config

BUG=chromium:869209
TEST=emerges

Change-Id: I73228de51221000312801719d8c9e77238da654b
Reviewed-on: https://chromium-review.googlesource.com/1197211
Commit-Ready: Zentaro Kavanagh <zentaro@chromium.org>
Tested-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
5 files changed