Implement googContentType GetStats metric reported on receive side.

webrtc/media/base/mediachannel.h

Index: webrtc/media/base/mediachannel.h
diff --git a/webrtc/media/base/mediachannel.h b/webrtc/media/base/mediachannel.h
index 1ab41231bf05cb908e29b81f709a92d4f4e01f7d..5aae309febc5dedf3f7bcc3d37d93fbf85a7ba06 100644
--- a/webrtc/media/base/mediachannel.h
+++ b/webrtc/media/base/mediachannel.h
@@ -771,6 +771,7 @@ struct VideoReceiverInfo : public MediaReceiverInfo {
         frames_decoded(0),
         frames_rendered(0),
         interframe_delay_max_ms(-1),
+        content_type(webrtc::VideoContentType::UNSPECIFIED),
         decode_ms(0),
         max_decode_ms(0),
         jitter_buffer_ms(0),
@@ -802,6 +803,8 @@ struct VideoReceiverInfo : public MediaReceiverInfo {
   rtc::Optional<uint64_t> qp_sum;
   int64_t interframe_delay_max_ms;
 
+  webrtc::VideoContentType content_type;
+
   // All stats below are gathered per-VideoReceiver, but some will be correlated
   // across MediaStreamTracks.  NOTE(hta): when sinking stats into per-SSRC
   // structures, reflect this in the new layout.