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

webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc

Index: webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc
diff --git a/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc b/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc
index 41fd7ff3845a8eb91f48fda76f322280f6f1d0dc..66db72c2922567afbcba9a60983b289edc1fd650 100644
--- a/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc
+++ b/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc
@@ -878,6 +878,9 @@
     encoded_images_[encoder_idx].capture_time_ms_ =
         input_image.render_time_ms();
     encoded_images_[encoder_idx].rotation_ = input_image.rotation();
+    encoded_images_[encoder_idx].content_type_ =
+        (codec_.mode == kScreensharing) ? VideoContentType::SCREENSHARE
+                                        : VideoContentType::UNSPECIFIED;
 
     int qp = -1;
     vpx_codec_control(&encoders_[encoder_idx], VP8E_GET_LAST_QUANTIZER_64, &qp);