Interface prototype objects and ES6 @@toStringTag

The way that WebIDL require Object.prototype.toString to return "[object
TypePrototype]" for the interface prototype object and "[object Type]" for
the instances seems to imply that every instance needs to have an own
@@toStringTag.

http://people.mozilla.org/~jorendorff/es6-draft.html#sec-15.2.4.2
http://dev.w3.org/2006/webapi/WebIDL/#es-environment

If an instance does not have its own @@toStringTag,
Object.prototype.toString will read through to the [[Prototype]] which
would return the wrong string.

-- 
erik