RTCIceCandidatePairStats.[total/current]RoundTripTime collected.

Collected in accordance with the spec:
https://w3c.github.io/webrtc-stats/#candidatepair-dict*

totalRoundTripTime is collected as the sum of rtt measurements, it was
previously not collected.
currentRoundTripTime is collected as the latest rtt measurement, it
was previously collected as a smoothed value, which was incorrect.

Connection is updated to collect these values which are surfaced
through ConnectionInfo.

BUG=webrtc:7062, webrtc:7204

Review-Url: https://codereview.webrtc.org/2719523002
Cr-Commit-Position: refs/heads/master@{#16905}
diff --git a/webrtc/api/stats/rtcstats_objects.h b/webrtc/api/stats/rtcstats_objects.h
index 29e2d76..baf0d28 100644
--- a/webrtc/api/stats/rtcstats_objects.h
+++ b/webrtc/api/stats/rtcstats_objects.h
@@ -144,14 +144,11 @@
   RTCStatsMember<bool> readable;
   RTCStatsMember<uint64_t> bytes_sent;
   RTCStatsMember<uint64_t> bytes_received;
-  // TODO(hbos): Collect and populate this value. https://bugs.webrtc.org/7062
   RTCStatsMember<double> total_round_trip_time;
-  // TODO(hbos): Collect this the way the spec describes it. We have a value for
-  // it but it is not spec-compliant. https://bugs.webrtc.org/7062
   RTCStatsMember<double> current_round_trip_time;
   RTCStatsMember<double> available_outgoing_bitrate;
   // TODO(hbos): Populate this value. It is wired up and collected the same way
-  // |VideoBwe.googAvailableReceiveBandwidth| is, but that value is always
+  // "VideoBwe.googAvailableReceiveBandwidth" is, but that value is always
   // undefined. https://bugs.webrtc.org/7062
   RTCStatsMember<double> available_incoming_bitrate;
   RTCStatsMember<uint64_t> requests_received;