What exactly is the replacement for getDefaultComputedStyle?

At one point we agreed to add Element.getDefaultComputedStyle to CSSOM 
to address the "what is the default (user+ua) value for this element for 
a given CSS property?" use case.

It looks like it's been removed from CSSOM at some point, but I see 
nothing replacing it.  Certainly none of the things on 
http://dev.w3.org/csswg/cssom/#getstyleutils cover this use case.  Am I 
just missing something?

The lack of such an API is causing libraries like jQuery to rely on 
weird display:none iframe hacks in an attempt to gather this sort of 
information.  And even with those hacks, if user/UA stylesheets have 
media query dependent styles there's no way for them to get correct answers.

-Boris