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 bc59900eff5cbd2c4d362df0742ab49d2482317f..8963db322ce122ddd2b4cf584fca365fe55ecb52 100644
--- a/webrtc/video/video_send_stream.cc
+++ b/webrtc/video/video_send_stream.cc
@@ -223,6 +223,7 @@ VideoSendStream::VideoSendStream(
   RTC_CHECK(ReconfigureVideoEncoder(encoder_config));
 
   vie_channel_->RegisterSendSideDelayObserver(&stats_proxy_);
+  vie_channel_->RegisterSendPacketObserver(&stats_proxy_);
 
   if (config_.post_encode_callback)
     vie_encoder_->RegisterPostEncodeImageCallback(&encoded_frame_proxy_);
@@ -537,6 +538,10 @@ int VideoSendStream::GetPaddingNeededBps() const {
   return vie_encoder_->GetPaddingNeededBps();
 }
 
+void VideoSendStream::OnSentPacket(int packet_id) {
+  stats_proxy_.OnSentPacket(packet_id);
+}
+
 bool VideoSendStream::SetSendCodec(VideoCodec video_codec) {
   static const int kEncoderMinBitrate = 30;
   if (video_codec.maxBitrate == 0) {