Non-fetch scheme navigation params initiator origin isn't always set correctly

[domfarolino]

Non-fetch scheme navigation params's initiator origin is populated in two places:

• https://html.spec.whatwg.org/#populating-a-session-history-entry:non-fetch-scheme-params-initiator-origin, in #attempt-to-populate, where we explicitly navigate to a non-fetch scheme URL
• https://html.spec.whatwg.org/#populating-a-session-history-entry:non-fetch-scheme-params-initiator-origin-2 in #create-navigation-params-by-fetching, when we redirect to a non-fetch scheme URL

The second instance above is setting the initiator origin to something completely bogus — the "origin" concept, not even a variable. I think this should instead be responseOrigin, to be the last fetch-scheme origin in the redirect chain, but need to take a closer look.