This allow to destroy the RtcpTransceiverImpl off the task queue with assumption it is destroyed after task queue. i.e. it allows to post destruction of RtcpTransceiverImpl to the TaskQueue without waiting. BUG: webrtc:8239 Change-Id: I4bea7a6d2edc97061ebd00f2f275c1ab827bc3c5 Reviewed-on: https://webrtc-review.googlesource.com/97160 Commit-Queue: Danil Chapovalov <danilchap@webrtc.org> Reviewed-by: Per Kjellander <perkj@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24574}