Add QP stats for received video streams to StatsReport.

webrtc/video/receive_statistics_proxy.h

Index: webrtc/video/receive_statistics_proxy.h
diff --git a/webrtc/video/receive_statistics_proxy.h b/webrtc/video/receive_statistics_proxy.h
index b6741f9cde163b7105462997d130436abc6db452..d05f5edf356085e9c9fa6d1416baa17a1306aec9 100644
--- a/webrtc/video/receive_statistics_proxy.h
+++ b/webrtc/video/receive_statistics_proxy.h
@@ -14,6 +14,7 @@
 #include <string>
 
 #include "webrtc/base/criticalsection.h"
+#include "webrtc/base/exp_filter.h"
 #include "webrtc/base/ratetracker.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/common_types.h"
@@ -106,6 +107,7 @@ class ReceiveStatisticsProxy : public VCMReceiveStatisticsCallback,
   SampleCounter delay_counter_ GUARDED_BY(crit_);
   ReportBlockStats report_block_stats_ GUARDED_BY(crit_);
   QpCounters qp_counters_;  // Only accessed on the decoding thread.
+  rtc::ExpFilter qp_;       // Only accessed on the decoding thread.
 };
 
 }  // namespace webrtc