Reland of Add content type information to encoded images and corresponding rtp extension header

webrtc/modules/rtp_rtcp/source/rtp_sender_video.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_sender_video.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_sender_video.cc b/webrtc/modules/rtp_rtcp/source/rtp_sender_video.cc
index 849ed78eadc07a94ad988683cef58c330701f89c..b89aefef53e44977f2bda96438bd16cb3b4572af 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_sender_video.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_sender_video.cc
@@ -324,6 +324,12 @@ bool RTPSenderVideo::SendVideo(RtpVideoCodecTypes video_type,
           current_rotation != kVideoRotation_0)
         rtp_header->SetExtension<VideoOrientation>(current_rotation);
       last_rotation_ = current_rotation;
+      // Report content type only for key frames.
+      if (frame_type == kVideoFrameKey &&
+          video_header->content_type != VideoContentType::UNSPECIFIED) {
+        rtp_header->SetExtension<VideoContentTypeExtension>(
+            video_header->content_type);
+      }
     }
 
     // FEC settings.