L. David Baron 24bffb840f Bug 1277709 - Make threadsafe reference counting use the minimum memory sychronization needed. r=froydnj
This uses std::atomic rather than mozilla::Atomic since mozilla::Atomic
does not support using different memory synchronization for different
atomic operations on the same variable.

The added comments could use careful review since, while they reflect my
understanding of the issue, I don't consider myself an expert on the
topic.

MozReview-Commit-ID: 7xByCXt17Dr

--HG--
extra : transplant_source : %8DM%88%E8%B7%B4%D8a%D6%F5%3F%9B%DC%09X%F3%7C%98%DE%21
2017-04-04 20:59:20 -07:00
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