Enforce username policy on Mac.
This version doesn't enforce the policy at the login screen--the host will run at the login screen, even if it is registered to an account other than that of the local user.
BUG=162070
TEST=Register to an account with a username other than that of your local login. Verify that the host shuts down as soon as it runs in the Aqua context.
Review URL: https://chromiumcodereview.appspot.com/
11414176
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@169557 0039d316-1c4b-4281-b951-d872f2087c98