Whitelist WebRTC Crypto stats fields

This unblocks https://webrtc-review.googlesource.com/c/src/+/158403

Bug: chromium:1018077
Change-Id: I7b660766daeabe1d3bdd8d25d98bcb78d8045091
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879253Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709490}

chrome/test/data/webrtc/peerconnection_getstats.js

@@ -489,6 +489,9 @@ let kRTCTransportStats = new RTCStats(null, {
   selectedCandidatePairId: 'string',
   localCertificateId: 'string',
   remoteCertificateId: 'string',
+  tlsVersion: 'string',
+  dtlsCipher: 'string',
+  srtpCipher: 'string',
   selectedCandidatePairChanges: 'number',
 });
 addRTCStatsToWhitelist(Presence.MANDATORY, 'transport', kRTCTransportStats);