Make BrowserContext spec-compliant

[jdm]

In practical terms, this means the frame tree on the script side should consist of BrowserContext values, with navigations causing the active document to be replaced. Any concept of a bfcache in the script task should store Document pointers.

Blocks #5236.

[benschulz]

I read "make BrowserContext spec-compliant" as "make BrowserContexts persist across document loads within them". I.e. HTMLFrameElement and HTMLIFrameElement each own an unchanging BrowserContext, which points to the document it's currently displaying.

How is that supposed to work w.r.t. cross-origin/different eTLD frames though? As far as I understand Documents should not escape their script task. Therefore the BrowserContext of a frame with a cross-origin src can't point to the document it's displaying.

What am I missing/misunderstanding?

[jdm]

Yes, we need to introduce a concept of opaque, proxy browsing contexts for cross-origin documents per #5242.

[KiChjang]

I believe we have since renamed the struct as BrowsingContext.

[jdm]

Much of this is addressed by #15120.

[KiChjang]

Should this be closed then?

[jdm]

I guess so!