[whatwg] Spec for location object needs to make some properties unforgeable; need supporting WebIDL changes

[Cameron McCormack]

Boris Zbarsky:
> So we have indications that making everything on this
> interface unforgeable is sufficiently web-compatible.

OK.  I propose then that we allow [Unforgeable] on the interface, which 
means:

* attributes get own, non-configurable accessor properties (with setters 
if they are not readonly attributes), and no property on the prototype
* operations get own, non-configurable, non-writable properties, and no 
property on the prototype
* the stringifier gets an own, non-configurable, non-writable toString 
property, and no property on the prototype
* there is an own, non-configurable, non-writable valueOf property that 
just returns this

I think that's the least amount of crazy.

This would make Location.prototype empty.  Is that OK?