Google Analytics and First party cookies

The way this works is that, as you saw, the base html makes a request for a script file. Though this script file comes from google. It's use is in the page from webmetrics. It is the webmetrics page that runs the script and therefore it is still a first party cookie. The script file is just the code that the base page will run.

In my trace this then goes and retrieves an image from google of a 1 pixel gif file. This request will then send the cookies that are created, enabling google to track the usage.