For use in AudiReceiveStream, introduce a new method GetSyncInfo. This change is analogous to https://webrtc-review.googlesource.com/91123, doing the same for RtpVideoStreamReceiver. It's a preparation for bypassing the RtpReceiver class. Bug: webrtc:7135 Change-Id: I87c1c6f0a1f28b0baebe07c4181f6f0427afa314 Reviewed-on: https://webrtc-review.googlesource.com/93022 Reviewed-by: Oskar Sundbom <ossu@webrtc.org> Commit-Queue: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24228}