libchromeos-ui: Add --arc-available

Since there is a Chrome Variation experiment that can enable ARC, we
still need a way to detect if it is available on the board. This will
avoid showing the opt-in dialog for boards that do not support it.

BUG=b:30230518
TEST=Self-built image with USE="cheets" did pass --arc-available

Change-Id: I43386432264d621dd1629d5cf533c9b64e66cab9
Reviewed-on: https://chromium-review.googlesource.com/373607
Commit-Ready: Luis Hector Chavez <lhchavez@google.com>
Tested-by: Luis Hector Chavez <lhchavez@google.com>
Reviewed-by: Dan Erat <derat@chromium.org>
1 file changed