Specify BFCache interaction

[nidhijaju]

The proposal for WebTransport interacting with BFCache is that we allow pages using WebTransport to enter the BFCache, but close the connection when navigating away. Then, the various promises will resolve if/when the page is navigated back to.

The spec currently already terminates the session in the unloading document cleanup steps, but this PR adds a step to queue a network task to run cleanup on a WebTransport object. The network task queue will be paused when the page is navigated away from, and resumed when the page is navigated back to.

Fixes #326.

cc @rakina

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Preview | Diff

[rakina]

Thanks for working on this! This is great, but recently the guidance on adding unloading document cleanup steps had changed, so instead of using the hook like this PR does, to define a stand-alone set of steps, that the HTML spec explicitly calls out to. This makes the ordering of the steps clear for all things that run at unloading-document-cleanup time.
(The BFCache guide was recently updated to reflect this as well)

So I think there are some more changes needed:

1. Instead of defining "unloading document cleanup steps" for HTML make it an independent thing (you can keep the name, or use "context cleanup steps" like the section heading says.
2. Update the HTML spec to call out to this step in the Web Transport spec from within the HTML spec's "unloading document cleanup steps"

Also, are there any implementation bugs filed for Chrome (and maybe Firefox) yet?

(thanks again!)

cc @domenic @fergald

[fergald]

Ping any progress on this? I would really like WT to have it's BFCache story straight from the start.