Re: [matrix][cssom-view] DOMPoint, DOMPointLiteral definitions

So here's a question for mutable vs immutable DOMRect stuff.

Are there any cases in which we'd want to return a mutable DOMRect where 
returning a dictionary wouldn't work just as well?

As in, do we really just want to have an immutable DOMRect type and a 
DOMRectLiteral dictionary, and have things like getBoundingClientRect() 
return the latter, say?

-Boris

P.S. In a super-ideal world we may be able to have an interface with the 
getters and then a derived interface with the setters, but there's no 
really good way to do that in ES: you have to put the getters on both 
interfaces.  Which is also an option, of course; it just leads to some 
surprising results if you try to interpose those getters on the 
less-derived interface from script.