Add histogram stats for send delay for a sent video stream.

webrtc/video/video_send_stream.cc

Index: webrtc/video/video_send_stream.cc
diff --git a/webrtc/video/video_send_stream.cc b/webrtc/video/video_send_stream.cc
index da0f3b760cefa240d95fb55429005a157e95642e..77d777b754fa281f4bb96c7ec968cba6d43fdff0 100644
--- a/webrtc/video/video_send_stream.cc
+++ b/webrtc/video/video_send_stream.cc
@@ -297,6 +297,7 @@ VideoSendStream::VideoSendStream(
   ReconfigureVideoEncoder(encoder_config);
 
   vie_channel_.RegisterSendSideDelayObserver(&stats_proxy_);
+  vie_channel_.RegisterSendPacketObserver(&stats_proxy_);
 
   if (config_.post_encode_callback)
     vie_encoder_.RegisterPostEncodeImageCallback(&encoded_frame_proxy_);
@@ -635,5 +636,9 @@ void VideoSendStream::OnBitrateUpdated(uint32_t bitrate_bps,
   vie_encoder_.OnBitrateUpdated(bitrate_bps, fraction_loss, rtt);
 }
 
+bool VideoSendStream::OnSentPacket(int packet_id) {
+  return stats_proxy_.OnSentPacket(packet_id);
+}
+
 }  // namespace internal
 }  // namespace webrtc