This change adds flags and default values for two more RTP header extensions: VideoContentType and VideoTiming. This will silence a number of annoying warnings when running with application logs. Bug: none Change-Id: I9bb01ea2519813d3c47553ecff384141fbede23e Reviewed-on: https://webrtc-review.googlesource.com/75300 Reviewed-by: Minyue Li <minyue@webrtc.org> Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23178}