The User Manager tutorial should disable pods in the single pod case too

BUG=357500
TEST=Delete all your profiles, start chrome with --new-profile-management.
From the avatar bubble, choose "Not Person 1". The user manager should come
up, it should display a tutorial to the side, and the only user pod showing
should be disabled and slightly opaque.

Review URL: https://codereview.chromium.org/217293003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@260667 0039d316-1c4b-4281-b951-d872f2087c98