The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform2/+/c524c614ccd378be03abc3c85627d822399234d2

commit c524c614ccd378be03abc3c85627d822399234d2
Author: Xiaochu Liu <xiaochu@chromium.org>
Date: Wed Oct 31 19:42:32 2018

dlcservice: support deciding current boot slot

The functions are copied from
src/aosp/system/update_engine/boot_control_chromeos.* and
src/aosp/system/update_engine/common/utils.h
along with the unittests.

We duplicate the code in update_engine mainly because update_engine is a
shared code base (aosp, chromium os) and we do not have a great way to
share in this case (libbrillo is an overkill and aosp merging in
update_engine could be troublesome).

BUG= chromium:898254 
TEST=unittest

Change-Id: I7214d963d1d392599d86dec3426e9477ddd202ba
Reviewed-on: https://chromium-review.googlesource.com/1299296
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Xiaochu Liu <xiaochu@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Xiaochu Liu <xiaochu@chromium.org>

[add] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/boot_device.cc
[add] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/boot_device_test.cc
[modify] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/dlc_service_dbus_adaptor.cc
[add] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/boot_slot_test.cc
[modify] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/dlc_service_dbus_adaptor.h
[modify] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/dlc_service.cc
[add] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/boot_slot.h
[add] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/mock_boot_device.h
[add] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/boot_slot.cc
[add] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/boot_device.h
[modify] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/BUILD.gn
[modify] https://crrev.com/c524c614ccd378be03abc3c85627d822399234d2/dlcservice/dlc_service_dbus_adaptor_test.cc