Correctly deal with tokens for supervised users in ProfileOAuth2TokenService.

TBR=antrim@chromium.org
BUG=279307,312751

Review URL: https://codereview.chromium.org/33173005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233393 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233393