This allows clients to move to these new accessors and off of the
sync_label field which is deprecated.
Bug: webrtc:7932
Change-Id: I32b30087bf1be380d607a649bd90fa9617dafeb9
Reviewed-on: https://webrtc-review.googlesource.com/58020
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22213}