[IndexedDB] Don't expose GC behavior (#29)

Original bug: https://www.w3.org/Bugs/Public/show_bug.cgi?id=25223

I added some text in bdfc9964855d0ad650ade6da3ed0dd9b43b69d6a but it's still the case that connections closed via GC make GC observable.

It's unclear that we can do better than what the spec currently says, but feedback welcome.

---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/IndexedDB/issues/29