GitLab

This CL adds a preference called kCrostiniEnabled (= "crostini.enabled")
and sets it to true when Crostini is installed.

Bug: 833125
Change-Id: I58f27113e49cdcbc1c4aaf99f5aa4096fcdab902
Reviewed-on: https://chromium-review.googlesource.com/1013843
Commit-Queue: Renée Wright <rjwright@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553926}