Move AutoLoginInfoBarDelegate to observing SigninManager

This change is part of the effort to eliminate Signin-related notifications.

BUG=345632
R=pkasting@chromium.org

Review URL: https://codereview.chromium.org/189373009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256209 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256209