Interaction with COOP

[domenic]

Cross-Origin-Opener-Policy prevents popups and parent pages from talking to each other, and is used by many modern pages for security reasons.

The interactions between COOP and this new type of popup will need to be figured out.

[ArthurSonzogni]

Assuming that:

1. PIP window are essentially a new popup. Its document is the initial empty document, inheriting properties the same way a window.open() popup does.
2. PIP window can't navigate elsewhere.
3. PIP window can't be created from an iframe.

Then, this would mean the PIP window PolicyContainer's COOP policy in this case is inherited from the opener, and we don't force 'noopener'. The opener/openee relationship is not broken by COOP (because no navigations).

IMO, the current behavior it would imply looks fine to me, assuming (1), (2), and (3) are right.

Yes, it would be nice being explicit about what is expected here.