[ServiceWorker] spec should be more explicit about accessing internal body on opaque Responses (#710)

>From reading the non-normative text it appears that respondWith() and Cache.put() should process the internal body of an opaque response.  This is confusing from the normative steps, however, since they only refer to the "body" which fetch defines as null for opaque responses.

It would be nice to explicitly reference the internal body in these cases in the normative text.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/710