Frame marking RTP header extension (PART 1: implement extension)

Bug: webrtc:7765
Change-Id: I23896d121afd6be4bce5ff4deaf736149efebcdb
Reviewed-on: https://webrtc-review.googlesource.com/85200
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24695}
diff --git a/api/rtp_headers.h b/api/rtp_headers.h
index c762534..41f3988 100644
--- a/api/rtp_headers.h
+++ b/api/rtp_headers.h
@@ -19,6 +19,7 @@
 #include "absl/types/optional.h"
 #include "api/array_view.h"
 #include "api/video/video_content_type.h"
+#include "api/video/video_frame_marking.h"
 #include "api/video/video_rotation.h"
 #include "api/video/video_timing.h"
 
@@ -116,6 +117,9 @@
   bool has_video_timing;
   VideoSendTiming video_timing;
 
+  bool has_frame_marking;
+  FrameMarking frame_marking;
+
   PlayoutDelay playout_delay = {-1, -1};
 
   // For identification of a stream when ssrc is not signaled. See