Eliminates manual reference counting logic, and one of the few remaining uses of the Atomic32 type. Bug: webrtc:8270 Change-Id: Ibbbf227c710f7e8f68a98bac46d3e24b7cb5ee2f Reviewed-on: https://webrtc-review.googlesource.com/14600 Commit-Queue: Niels Moller <nisse@webrtc.org> Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20393}