GitLab

The change is mostly mechanical replacing defined(OS_CHROMEOS) with
BUILDFLAG(IS_CHROMEOS_ASH) and GN variable is_chromeos with
is_chromeos_ash with some special cases (For those cases please
refer to http://go/lacros-macros).

The patch is made in preparation to switching lacros build from
target_os=linux to target_os=chromeos. This will prevent lacros from
changing behaviour after the switch.

Bug: 1052397
Change-Id: Iad750ef52b3a42cc0339e8e6fdb682c4cf397b16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2550844Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Wei Li <weili@chromium.org>
Commit-Queue: Yuta Hijikata <ythjkt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833996}