Add QP stats for sent video streams to StatsReport.

webrtc/video/send_statistics_proxy.cc

Index: webrtc/video/send_statistics_proxy.cc
diff --git a/webrtc/video/send_statistics_proxy.cc b/webrtc/video/send_statistics_proxy.cc
index 5c2052a207868d9c6b2e5c7bd4e7edbb0a83d7e1..efd53fc043c97557349e12822f63d491330c2ebc 100644
--- a/webrtc/video/send_statistics_proxy.cc
+++ b/webrtc/video/send_statistics_proxy.cc
@@ -126,6 +126,11 @@ void SendStatisticsProxy::UpdateHistograms() {
     RTC_HISTOGRAM_COUNTS_100000(
         "WebRTC.Video.SendSideDelayMaxInMs", max_delay_ms);
   }
+  for (const auto& it : qp_counters_) {
+    int qp = it.second.vp8.Avg(kMinRequiredSamples);
+    if (qp != -1)
+      RTC_HISTOGRAM_COUNTS_200("WebRTC.Video.Encoded.Vp8.Qp", qp);
+  }
 }
 
 void SendStatisticsProxy::OnOutgoingRate(uint32_t framerate, uint32_t bitrate) {
@@ -243,6 +248,13 @@ void SendStatisticsProxy::OnSendEncodedImage(
          encoded_image.adapt_reason_.bw_resolutions_disabled);
     }
   }
+  if (encoded_image.qp_ != -1 && rtp_video_header != nullptr) {
+    if (rtp_video_header->codec == kRtpVideoVp8) {
+      qp_counters_[ssrc].vp8.Add(encoded_image.qp_);
+      qp_filters_[ssrc].qp.Apply(1.0f, encoded_image.qp_);
+      stats->qp = round(qp_filters_[ssrc].qp.filtered());
+    }
+  }
 
   // TODO(asapersson): This is incorrect if simulcast layers are encoded on
   // different threads and there is no guarantee that one frame of all layers