you can probably do this already by turning on the flag for generic builders like amd64-generic and arm-generic

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/6a3bb5a8b978e668f2e28a37e385d9c10b2fb626

commit 6a3bb5a8b978e668f2e28a37e385d9c10b2fb626
Author: Xiaochu Liu <xiaochu@chromium.org>
Date: Wed Nov 14 14:27:15 2018

overlay-amd64-generic: use dlc USE flag

We build/run dlc use flag so we can have pre-cq coverage.

BUG= chromium:903887 
TEST=tryjob pre-cq
CQ-DEPEND=CL:1330164

Change-Id: I7a0c3a5305c0f37e6770da4e209f001fbf72ad6f
Reviewed-on: https://chromium-review.googlesource.com/1329823
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Xiaochu Liu <xiaochu@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/6a3bb5a8b978e668f2e28a37e385d9c10b2fb626/overlay-amd64-generic/profiles/base/make.defaults

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/b7cbf488c1bd43d2393bbe0ba577d1c37589ef99

commit b7cbf488c1bd43d2393bbe0ba577d1c37589ef99
Author: Xiaochu Liu <xiaochu@chromium.org>
Date: Wed Nov 14 14:27:16 2018

overlay-arm-generic: use dlc USE flag

We build/run dlc use flag so we can have pre-cq coverage.

BUG= chromium:903887 
TEST=tryjob pre-cq
CQ-DEPEND=CL:1329823

Change-Id: Ifec3854e24ee983cb77725913415f87e6195813c
Reviewed-on: https://chromium-review.googlesource.com/1331927
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Xiaochu Liu <xiaochu@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[modify] https://crrev.com/b7cbf488c1bd43d2393bbe0ba577d1c37589ef99/overlay-arm-generic/profiles/base/make.defaults

Checked amd64-generic and arm-generic on pre-cq and verified dlcservice and dlcservice-client packages are built during UnitTest stage.