[ServiceWorker] self.caches should spec what to do for "untrusted" origins (#687)

Currently `self.caches` is spec'd to always return a CacheStorage object.  Clearly, there are cases where this should not be done.  For example, in a context with a synthetic origin such as a sandboxed iframe or data URI worker.  The spec does not say what to do in these cases.

The web-platform-tests from blink show that the blink implementation throws SecurityError in this case.  That seems reasonable.

I believe @ehsan would prefer we just hide the `self.caches` property in these cases.

Thoughts?

@jakearchibald @slightlyoff @jungkees @annevk 

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/687