Mehrdad, Kentico doesn't have that with Google out of box. So you will have to create your own. If the login page Brenden mentioned above works for you and you only need the Google link button below the FB button, then just use an image link.
If you want the similar web part like the FB one, you may want to checkout how that one is implemented
\CMS\CMSWebParts\Membership\FacebookConnect\FacebookConnectLogon.ascx