[webidl] Promise type on an attribute should be allowed (#71)

Because Promise<T> types are reference types, the [SameObject] extended attribute should be permitted for use with them. In the current spec, they are forbidden by the restriction:

[4.3.15. SameObject](http://heycam.github.io/webidl/#SameObject)
> The [SameObject] extended attribute MUST NOT be used on anything other than a read only attribute whose type is an interface type or object.

(Unless Promise<T> is to be understood as an interface type.)

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Reply to this email directly or view it on GitHub:
https://github.com/heycam/webidl/issues/71