Moved from RtpSender to RtpSenderVideo, since currently the PlayoutDelay extension is used for video only, and configured via RTPVideoHeader. Bug: webrtc:7135 Change-Id: Idfcc90cefea83e40a4e79164d7914cdcd50e41fe Reviewed-on: https://webrtc-review.googlesource.com/c/120357 Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Commit-Queue: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#26484}