Where does `googleUser` come from?

https://github.com/firebase/snippets-web/blob/1c4c6834f310bf53a98b3fa3c2e2191396cacd69/snippets/auth-next/google-signin/auth_google_checksameuser.js#L15

I know that `firebaseUser` comes from this ( `result.user`):
```
signInWithPopup(auth, provider)
.then((result) => {
// This gives you a Google Access Token. You can use it to access the Google API.
const credential = GoogleAuthProvider.credentialFromResult(result);
const token: string | undefined = credential?.accessToken;
// The signed-in user info.
const user = result.user;
.....
```

But where does `googleUser` come from?