GitLab

The old UMA hw class API is kept behind a base::Feature in case
we need to revert.

Also updates some comments where we were using ChromeOS instead
of Chrome OS, which is preferred.

Bug: 810872
Change-Id: I6ca101432da58ca36ec0d4a85cca745e7700257b
Reviewed-on: https://chromium-review.googlesource.com/978518Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546150}