Add QP sum stats for received streams.

webrtc/pc/statscollector.cc

Index: webrtc/pc/statscollector.cc
diff --git a/webrtc/pc/statscollector.cc b/webrtc/pc/statscollector.cc
index 3e0c2bf4414354fc6d44547aaa97f15252a3f590..e91f873824a245ee7284f5a6e154908be627e258 100644
--- a/webrtc/pc/statscollector.cc
+++ b/webrtc/pc/statscollector.cc
@@ -221,6 +221,9 @@ void ExtractStats(const cricket::VideoReceiverInfo& info, StatsReport* report) {
     report->AddInt64(StatsReport::kStatsValueNameCaptureStartNtpTimeMs,
                      info.capture_start_ntp_time_ms);
   }
+  if (info.qp_sum)
+    report->AddInt64(StatsReport::kStatsValueNameQpSum, *info.qp_sum);
+
   const IntForAdd ints[] = {
     { StatsReport::kStatsValueNameCurrentDelayMs, info.current_delay_ms },
     { StatsReport::kStatsValueNameDecodeMs, info.decode_ms },