Wire up RTCInboundRtpStreamStats.lastPacketReceivedTimestamp.

This collects this metric for both audio and video streams.
https://w3c.github.io/webrtc-stats/#dom-rtcinboundrtpstreamstats-lastpacketreceivedtimestamp

This is a follow-up to https://webrtc-review.googlesource.com/c/src/+/130479
which calculated this metric. This CL is purely plumbing from
"StreamDataCounters::last_packet_received_timestamp_ms" to
RTCInboundRtpStreamStats.


Bug: webrtc:10449
Change-Id: I757ad19b5b8e84553da5edd4a75efa3e1fe30b56
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/131397
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27628}
diff --git a/api/stats/rtcstats_objects.h b/api/stats/rtcstats_objects.h
index 8a1fe56..81ec084 100644
--- a/api/stats/rtcstats_objects.h
+++ b/api/stats/rtcstats_objects.h
@@ -397,6 +397,7 @@
   RTCStatsMember<uint32_t> packets_received;
   RTCStatsMember<uint64_t> bytes_received;
   RTCStatsMember<int32_t> packets_lost;  // Signed per RFC 3550
+  RTCStatsMember<double> last_packet_received_timestamp;
   // TODO(hbos): Collect and populate this value for both "audio" and "video",
   // currently not collected for "video". https://bugs.webrtc.org/7065
   RTCStatsMember<double> jitter;