Users of the mixer can use this information to determine which sources were included in the frame.
Bug: webrtc:12745
Change-Id: I11a8e3b1f4e8f95eb870336cad8dd082330bdf02
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/217768
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Minyue Li <minyue@webrtc.org>
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Reviewed-by: Chen Xing <chxg@google.com>
Commit-Queue: Doudou Kisabaka <doudouk@google.com>
Cr-Commit-Position: refs/heads/master@{#34035}
fe6595f006