This part of the effort to implement A/V sync metric. Bug: webrtc:10739 Change-Id: I4adba1b99b37b31868168e37d9aa8e03f8ea6d4e Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/159886 Commit-Queue: Ruslan Burakov <kuddai@webrtc.org> Reviewed-by: Björn Terelius <terelius@webrtc.org> Reviewed-by: Minyue Li <minyue@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Reviewed-by: Ruslan Burakov <kuddai@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29849}