如果您使用的是Google+登录，则用户需要升级其Google帐户以包括Google+.如果用户尝试登录，拥有Google帐户且尚未升级，则登录按钮将在用户登陆您的网站之前对其进行升级.

If you're using Google+ Sign-in, the user will need to have upgraded their Google account to include Google+. If the user tries to sign in, has a Google account, and hasn't upgraded, the sign-in button will upgrade them before they land on your site.