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

webrtc/test/fake_encoder.cc

Index: webrtc/test/fake_encoder.cc
diff --git a/webrtc/test/fake_encoder.cc b/webrtc/test/fake_encoder.cc
index 1db93eb40e36b6ebc87089a6171b438bfdfa907c..fce12c61a804c8af841435b001779374b912066c 100644
--- a/webrtc/test/fake_encoder.cc
+++ b/webrtc/test/fake_encoder.cc
@@ -61,6 +61,7 @@
   int max_target_bitrate_kbps;
   int64_t last_encode_time_ms;
   size_t num_encoded_bytes;
+  VideoCodecMode mode;
   {
     rtc::CritScope cs(&crit_sect_);
     max_framerate = config_.maxFramerate;
@@ -73,6 +74,7 @@
     max_target_bitrate_kbps = max_target_bitrate_kbps_;
     last_encode_time_ms = last_encode_time_ms_;
     num_encoded_bytes = sizeof(encoded_buffer_);
+    mode = config_.mode;
   }
 
   int64_t time_now_ms = clock_->TimeInMilliseconds();
@@ -142,6 +144,9 @@
     encoded._encodedWidth = simulcast_streams[i].width;
     encoded._encodedHeight = simulcast_streams[i].height;
     encoded.rotation_ = input_image.rotation();
+    encoded.content_type_ = (mode == kScreensharing)
+                                ? VideoContentType::SCREENSHARE
+                                : VideoContentType::UNSPECIFIED;
     specifics.codec_name = ImplementationName();
     RTC_DCHECK(callback);
     if (callback->OnEncodedImage(encoded, &specifics, nullptr).error !=