chromiumos: add FIRMWARE_LCOV artifact type

Add artifact type for code coverage data that we use in firmware-ec
builds.

BUG=b:156895937
TEST=generate

Change-Id: I6876f3c3922d11a8e37ffc26d25face50d56b6be
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2678131
Reviewed-by: LaMont Jones <lamontjones@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: LaMont Jones <lamontjones@chromium.org>
4 files changed