McAfee SECURE Safe Browsing shows Gmail doesn't have a valid SSL?

I'm not sure where to ask this, so please move to the correct place if needed. I'm curious as to the security of Gmail. I have the extension McAfee SECURE Safe Browsing from the Chrome Store, and when checking it on Gmail it shows No SSL. Why is that? I checked other email providers like Outlook and Yahoo, and both show Valid SSL. Can someone please explain this? Here are two examples. Gmail shows No SSL, and Yahoo shows Valid SSL. Is Gmail not as safe/secure? Why do some show Valid SSL and some do not even though they both start the same with HTTPS?

EDIT on findings: I've done some other checks on other Google pages, and they show Valid SSL (Checked Google+ and Google search). It seems only Gmail shows No SSL.