[libchromeos] add Platform

This class is being moved from cryptohome so it can be used elsewhere
(login_manager primarily).

BUG=chromium-os:34536
TEST=build

Change-Id: I979f70e3f783bb64a46238678606937b3f3b98e9
Signed-off-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/33536
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
6 files changed