Retrieve enterprise device state in OOBE.

This extends AutoEnrollmentClient to be able to retrieve server-backed
device state from the cloud during OOBE. This will allow the device to
restore enrollment state after recovery.

BUG=chromium:351663
TEST=Existing unit tests.
R=joaodasilva@chromium.org

Review URL: https://codereview.chromium.org/197043002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257115 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257115