Also prepared it for comming changes to RTPVideoHeader.
Bug: none
Change-Id: I60e57f779aee4ee98b6eec3d6631e43ac682c37f
Reviewed-on: https://webrtc-review.googlesource.com/87825
Reviewed-by: Alex Loiko <aleloi@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23911}