Create a VideoFrameTrackingId RTP header extension.

Bug: webrtc:12594
Change-Id: I518b549b18143f4711728b4637a4689772474c45
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212084
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/master@{#33567}

docs/native-code/rtp-hdrext/video-frame-tracking-id/README.md

@@ -0,0 +1,27 @@
+# Video Frame Tracking Id
+
+The Video Frame Tracking Id extension is meant for media quality testing
+purpose and shouldn't be used in production. It tracks webrtc::VideoFrame id
+field from the sender to the receiver to gather referenced base media quality
+metrics such as PSNR or SSIM.
+Contact <jleconte@google.com> for more info.
+
+**Name:** "Video Frame Tracking Id"
+
+**Formal name:**
+<http://www.webrtc.org/experiments/rtp-hdrext/video-frame-tracking-id>
+
+**Status:** This extension is defined to allow for media quality testing. It is
+enabled by using a field trial and should only be used in a testing environment.
+
+### Data layout overview
+     1-byte header + 2 bytes of data:
+
+      0                   1                   2
+      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     |  ID   | L=1   |    video-frame-tracking-id    |
+     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+Notes: The extension shoud be present only in the first packet of each frame.
+If attached to other packets it can be ignored.