The change ships GenericDescriptor00 and authentication by default, but doesn't expose it by default, and makes WebRTC respond to offers carrying it. The change adds a unit test for the new semantics. Tests well in munge-sdp. Frame marking replaced by http://www.webrtc.org/experiments/rtp-hdrext/generic-frame-descriptor-00 in the offer results in an answer containing the extension as first entry. Bug: webrtc:11367 Change-Id: I0ef91b7d4096d949c3d547ece7d6c4d39aa241da Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168661 Reviewed-by: Magnus Flodman <mflodman@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Commit-Queue: Markus Handell <handellm@webrtc.org> Cr-Commit-Position: refs/heads/master@{#30542}