This change replaces the `ContributingSources`-implementation of `GetContributingSources()` and `GetSynchronizationSources()` on the audio side with the spec-compliant `SourceTracker`-implementation.
The most noticeable impact is that the per-frame dictionaries are now updated when frames are delivered to the RTCRtpReceiver's MediaStreamTrack rather than when RTP packets are received on the network.
This change is almost identical to the previous video side change at: https://webrtc-review.googlesource.com/c/src/+/143177
Bug: webrtc:10545
Change-Id: Ife7f08ee8ca1346099b7466837a3756947085fc5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/144422
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Chen Xing <chxg@google.com>
Cr-Commit-Position: refs/heads/master@{#28459}
8fa7151e4b