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

webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc

Index: webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
diff --git a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
index 4d7df867a27196afaa115ca72c69ac13d0df7ea2..4b0f99e324a31bbf5de1e756e0fa773f73c14f69 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -706,6 +706,9 @@
     encoded_image_._timeStamp = input_image_->timestamp();
     encoded_image_.capture_time_ms_ = input_image_->render_time_ms();
     encoded_image_.rotation_ = input_image_->rotation();
+    encoded_image_.content_type_ = (codec_.mode == kScreensharing)
+                                       ? VideoContentType::SCREENSHARE
+                                       : VideoContentType::UNSPECIFIED;
     encoded_image_._encodedHeight = raw_->d_h;
     encoded_image_._encodedWidth = raw_->d_w;
     int qp = -1;