Implement googContentType GetStats metric reported on receive side.

webrtc/video/receive_statistics_proxy.cc

Index: webrtc/video/receive_statistics_proxy.cc
diff --git a/webrtc/video/receive_statistics_proxy.cc b/webrtc/video/receive_statistics_proxy.cc
index 2448bad746f32e2b0d740152ae59313a7c941753..ff4c6fef70ed8151e6a81b03f0a1a6bfe883a35a 100644
--- a/webrtc/video/receive_statistics_proxy.cc
+++ b/webrtc/video/receive_statistics_proxy.cc
@@ -501,6 +501,7 @@ VideoReceiveStream::Stats ReceiveStatisticsProxy::GetStats() const {
   stats_.interframe_delay_max_ms =
       interframe_delay_max_moving_.Max(now_ms).value_or(-1);
   stats_.timing_frame_info = timing_frame_info_counter_.Max(now_ms);
+  stats_.content_type = last_content_type_;
   return stats_;
 }