Client being null for client requests doesn't work with fetch groups

[annevk]

Something is wrong with the current model, but I haven't had the chance to investigate how it should work instead.

(The other day I overheard that Gecko has both a triggering and loading principal, whereas the specification does not have such a distinction. There's clearly room for some digging and improvement here.)

[annevk]

I have the feeling that triggering/loading is relevant for navigating, not necessarily for fetch in general. HTML has a "source browsing context" feature. Still, it seems impossible to set client to a useful value so I guess there's some special thing navigate has to do to associate its fetch with the fetch registry. Hmm.

[annevk]

https://groups.google.com/d/msg/mozilla.dev.platform/h9AyKjgCd_4/he_1vwnrOQAJ has notes on how we should solve this. Basically navigation needs to be responsible for creating a "fetch group". Workers also need to create one. Then there's also some complicated cases around object and embed elements.