What would happen to your website (or millions of websites) if one of the CDN's that you rely on started quietly issuing evil code to a few, targeted users? Would you notice? Would your users?
I don't think that it'd be too hard for us to add a simple API call that pokes data about screen resolution, browser agent string, language, etc upon load or login, and it'll be far more efficient and private than us sending random data off to GA or similar where they frequently don't even provide us IP addresses of our own site visitors so that we can correlate the data against our own logs.
The data that GA gathers is highly valuable... to Google. They only provide you visibility of the tippy tip of the iceberg.. but ultimately it's your customers' and your data, not theirs.
Don't compromise your users with third-party includes, even Google Fonts (which is still our last holdout on the website.. hm, someone should make a simple web app that gathers names and styles of fonts and provides a zip w/ pre-generated CSS.)
CDN's sound great but they're a huge privacy hole. Ask yourself; what's the profit model? Are they really just an opportunity to gather valuable data on other people's websites and browsing habits? (yes).
Please don't leak your customers' data.