chromeos: Support turning displays off in extended mode.

This makes OutputConfigurator support requests from powerd
that either the primary or secondary monitor be turned off
in extended desktop mode.  Previously, the panel always
remained on.

BUG=218387


Review URL: https://chromiumcodereview.appspot.com/13006006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@191558 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed