[Uno-d] Limit Sign in notification to extensions if Chrome not signed in

With Explicit browser sign in, it is possible that the user is signed in
to the web but not to Chrome. This CL ensures no Sign in events are
fired if the user is not signed in to Chrome.

Bug: b/321900930
Change-Id: Iabdab7dbb7ff9a8c9df0689261901b59afad5989
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5615152


Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Monica Basta <msalama@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1312989}