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.cc b/api/rtp_headers.cc
index a0b1a15..da7f1ea 100644
--- a/api/rtp_headers.cc
+++ b/api/rtp_headers.cc
@@ -34,7 +34,9 @@
       videoRotation(kVideoRotation_0),
       hasVideoContentType(false),
       videoContentType(VideoContentType::UNSPECIFIED),
-      has_video_timing(false) {}
+      has_video_timing(false),
+      has_frame_marking(false),
+      frame_marking({false, false, false, false, false, 0xFF, 0, 0}) {}
 
 RTPHeaderExtension::RTPHeaderExtension(const RTPHeaderExtension& other) =
     default;