Implement document.domain

[DavidBruant]

This is related to #633.
document.domain changes the origin of a document. Any current and coming optimizations based on the assumption that the origin of a document not changing over time like the recent Make sandboxed iframes run with different script tasks may require removing these optimizations later.

For that reason, I feel it'd be important to implement document.domain early and start using it in Servo tests to make sure Servo is actually running the web and not an idealized version

For the specific case of sandbox iframes and document.domain, it's been discussed in standards, there was agreement among the few who participated in the discussion and a solution has been implemented in Firefox (poison document.domain setter in sandboxed iframes regardless of allow-same-origin).
Assuming this sticks, this particular optimization will remain.

[bzbarsky]

Actually, need to neuter indexed/named access to subframes too. Or make it async. Or something.

[bzbarsky]

And in particular, if that access gets you a same-origin frame, there's a possible problem

[frewsxcv]

Visiting for triage: as of today, this is still not done

servo/components/script/dom/webidls/Document.webidl

Line 78 in a1cd27e

// attribute DOMString domain;

[mbrubeck]

Fixed by #8655.

[samlh]

I think the document.domain setter is still missing.

[asajeffrey]

Some discussion on IRC with @bzbarsky that's relevant to mutating document.domain: http://logs.glob.uno/?c=mozilla%23servo&s=6+Jan+2017&e=6+Jan+2017#c588833. See #14892.

[asajeffrey]

A first-cut implementation for the setter: asajeffrey@7aaa5c6

[asajeffrey]

A PR for the setter: #15536.