This is step 1: Encapsulating the data.
Bug: webrtc:12837
Change-Id: I15df30dc294c90136a90b072608ed4c2e8925dcb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/221602
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34245}