There’s a bunch of stuff in Chrome that’s special-cased to only allow Google to access it.
Not sure if it’s still there, but many years ago I was trying to figure out how to do something that some Google webapp was doing (can’t remember which one). I think it was something to do with popping up a chromeless window - that is, a new window with no address bar or browser chrome, just some HTML content.
Turns out the Chromium codebase had a hard-coded allowlist that only allowed *.google.com to use the API!
Edit: my memory was a bit wrong. It was this: stackoverflow.com/a/11614605. The Hangouts extension was allowlisted to use the functionality, but if any other extension wanted to use it, the user had to enable an experimental setting.