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/stats/rtcstats_objects.cc b/stats/rtcstats_objects.cc
index 99594a8..b1a1a23 100644
--- a/stats/rtcstats_objects.cc
+++ b/stats/rtcstats_objects.cc
@@ -617,6 +617,7 @@
     &key_frames_decoded,
     &total_decode_time,
     &content_type,
+    &estimated_playout_timestamp,
     &decoder_implementation)
 // clang-format on
 
@@ -650,6 +651,7 @@
       key_frames_decoded("keyFramesDecoded"),
       total_decode_time("totalDecodeTime"),
       content_type("contentType"),
+      estimated_playout_timestamp("estimatedPlayoutTimestamp"),
       decoder_implementation("decoderImplementation") {}
 
 RTCInboundRTPStreamStats::RTCInboundRTPStreamStats(
@@ -678,6 +680,7 @@
       key_frames_decoded(other.key_frames_decoded),
       total_decode_time(other.total_decode_time),
       content_type(other.content_type),
+      estimated_playout_timestamp(other.estimated_playout_timestamp),
       decoder_implementation(other.decoder_implementation) {}
 
 RTCInboundRTPStreamStats::~RTCInboundRTPStreamStats() {}