Bug 999888: Make IOInterposer leakcheck-friendly; f=ehsan, r=froydnj

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extra : rebase_source : ff65dd0f8ab4f28bf53b52f71cda1793df9a108a
Bug 999888: Make ObserverLists not use mozilla::AtomicRefCounted; r=froydnj

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extra : rebase_source : a1a29242b9a8d6e265d20352d9f24d743f20a47c