[fetch] Redirected range requests and preflights. (#145)

Chrome has some funky behavior around HTMLMediaElement + redirected range requests.

https://codereview.chromium.org/1220963004 denied responses to range requests if their origin is distinct from the origin response for the initial request.

https://codereview.chromium.org/1356353003 relaxes that restriction to accept responses to range requests if they're CORS-same-origin with the origin response from the initial request. It also treats "range" as a simple header for the purposes of preflights if the request is CORS enabled (e.g. `<video crossorigin ...>`).

It would be nice to spec this out in a sane way. :)

---
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fetch/issues/145