Now update the playout delay and related stats on the worker thread. This was previously reviewed here: https://webrtc-review.googlesource.com/c/src/+/172929/ With the exception of reducing unnecessarily broad lock scope in one function in rtp_rtcp_impl.cc and added comments in rtp_streams_synchronizer.h Bug: webrtc:11489 Change-Id: I77807b5da2accfe774255d9409542d358f288993 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/174200 Commit-Queue: Tommi <tommi@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Cr-Commit-Position: refs/heads/master@{#31193}