DNR: Add excludedTopFrameDomains (and topFrameDomains)

[ghostwords]

In addition to excludedInitiatorDomains (and initiatorDomains). Having excludedTopFrameDomains (and topFrameDomains) would solve the problem of excluding (or including) requests based specifically on the top-level document's domain, not the initiator's (immediate parent frame's) domain.

excludedTopFrameDomains will work just like excludedInitiatorDomains with the one difference being that excludedTopFrameDomains compares against the top-level frame's domain instead of the immediate parent frame's domain.

Developers should be able to feature detect the availability of excludedTopFrameDomains, so that they can use it when it is available and fall back on excludedInitiatorDomains otherwise.

For a real world example of what this would solve, see EFForg/privacybadger#3048 (comment)

[oliverdunk]

Chrome is supportive of this. It seems like a compelling use case and a good proposal to achieve the desired behavior.

[Rob--W]

What is the expected behavior if the top level is about:blank, e.g. a popup opened by https://example.com ?

[ghostwords]

We should fall back on the initiator in this edge case? Maybe we also want matchAboutBlank and matchOriginAsFallback properties? #673 seems related.