Adding vpn back to NetworkLibrary::active_network().

      This reverts part of rev/163676.
Adapting the non-vpn-network menu entry to not show VPN.

BUG=166589


Review URL: https://chromiumcodereview.appspot.com/11616015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@174150 0039d316-1c4b-4281-b951-d872f2087c98