Get WebRTC.Video.ReceivedPacketsLostInPercent from ReceiveStatistics

Old way to produce this histogram was based on RtcpStatisticsCallback
reporting sent RTCP messages, with some additional processing by the
ReportBlockStats class. After this cl, to grand average fraction loss
is computed by StreamStatistician, queried by VideoReceiveStream when
the stream is closed down, and passed to ReceiveStatisticsProxy which
produces histograms.

This is a preparation for deleting the RtcpStatisticsCallback from
ReceiveStatistics.

Bug: webrtc:10679
Change-Id: Ie37062c1ae590fd92d3bd0f94c510e135ab93e8d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/147722
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28747}

modules/rtp_rtcp/source/receive_statistics_impl.h

@@ -39,6 +39,7 @@ class StreamStatisticianImpl : public StreamStatistician,
   bool GetActiveStatisticsAndReset(RtcpStatistics* statistics);
   void GetDataCounters(size_t* bytes_received,
                        uint32_t* packets_received) const override;
+  absl::optional<int> GetFractionLostInPercent() const override;
   void GetReceiveStreamDataCounters(
       StreamDataCounters* data_counters) const override;
   uint32_t BitrateReceived() const override;