This is a preparation for deleting the class StringRtpHeaderExtension. Bug: webrtc:10440 Change-Id: I3480e58d96e67d10c4d78597c8ab7f01b63e37ca Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/128761 Commit-Queue: Niels Moller <nisse@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#27228}