R1:11786fb1cc84

Don't try to set anonymous session cookie on CDN/file domain

Summary:
Ref T2380. If an install has a CDN domain configured, but does not list it as an alternate domain (which is standard/correct, but not incredibly common, see T2380), we'll currently try to set anonymous cookies on it. These will correctly fail security rules.

Instead, don't try to set these cookies.

I missed this in testing yesterday because I have a file domain, but I also have it configured as an alternate domain, which allows…