Add estimatedPlayoutTimestamp to RTCInboundRTPStreamStats.

https://w3c.github.io/webrtc-stats/#dom-rtcinboundrtpstreamstats-estimatedplayouttimestamp

Partial implementation: currently only populated when a/v sync is enabled.

Bug: webrtc:7065
Change-Id: I8595cc848d080d7c3bef152462a9becf0e5a2196
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/155621
Commit-Queue: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29581}
diff --git a/pc/rtc_stats_collector.cc b/pc/rtc_stats_collector.cc
index 9d6cf77..ab12c65 100644
--- a/pc/rtc_stats_collector.cc
+++ b/pc/rtc_stats_collector.cc
@@ -285,6 +285,10 @@
             *voice_receiver_info.last_packet_received_timestamp_ms) /
         rtc::kNumMillisecsPerSec;
   }
+  if (voice_receiver_info.estimated_playout_ntp_timestamp_ms) {
+    inbound_audio->estimated_playout_timestamp = static_cast<double>(
+        *voice_receiver_info.estimated_playout_ntp_timestamp_ms);
+  }
   inbound_audio->fec_packets_received =
       voice_receiver_info.fec_packets_received;
   inbound_audio->fec_packets_discarded =
@@ -322,6 +326,10 @@
             *video_receiver_info.last_packet_received_timestamp_ms) /
         rtc::kNumMillisecsPerSec;
   }
+  if (video_receiver_info.estimated_playout_ntp_timestamp_ms) {
+    inbound_video->estimated_playout_timestamp = static_cast<double>(
+        *video_receiver_info.estimated_playout_ntp_timestamp_ms);
+  }
   // TODO(https://crbug.com/webrtc/10529): When info's |content_info| is
   // optional, support the "unspecified" value.
   if (video_receiver_info.content_type == VideoContentType::SCREENSHARE)