Add histogram stats for average QP per frame for VP8 (for sent video streams):

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 6407cdc62ea8e2257994ef90291f60c81ec42294..f3ca13811be377706931441ec765571746ba65ab 100644
--- a/webrtc/video/send_statistics_proxy.cc
+++ b/webrtc/video/send_statistics_proxy.cc
@@ -13,6 +13,7 @@
 #include <algorithm>
 #include <cmath>
 #include <map>
+#include <vector>
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
@@ -191,6 +192,11 @@ void SendStatisticsProxy::UmaSamplesContainer::UpdateHistograms(
     RTC_HISTOGRAMS_COUNTS_100000(kIndex, uma_prefix_ + "SendSideDelayMaxInMs",
                                  max_delay_ms);
   }
+  for (const auto& it : qp_counters_) {
+    int qp = it.second.vp8.Avg(kMinRequiredSamples);
+    if (qp != -1)
+      RTC_HISTOGRAMS_COUNTS_200(kIndex, uma_prefix_ + "Encoded.Qp.Vp8", qp);

[pbos-webrtc, 2016/03/22 15:35:12]

Should these be reported separately per simulcast layer? (Like this when we only
send one layer, but per-layer when we do simulcast)

[åsapersson, 2016/03/23 10:57:33]

Have updated to use a separate histogram per spatial layer. PTAL.

+  }
 
   if (first_rtcp_stats_time_ms_ != -1) {
     int64_t elapsed_sec =
@@ -426,6 +432,12 @@ void SendStatisticsProxy::OnSendEncodedImage(
     }
   }
 
+  if (encoded_image.qp_ != -1 && rtp_video_header != nullptr) {
+    if (rtp_video_header->codec == kRtpVideoVp8) {
+      uma_container_->qp_counters_[ssrc].vp8.Add(encoded_image.qp_);
+    }
+  }
+
   // TODO(asapersson): This is incorrect if simulcast layers are encoded on
   // different threads and there is no guarantee that one frame of all layers
   // are encoded before the next start.