White list networkType in RTCIceCandidateStats

networkType has been added in WebRTC code and it will be merged to
chromium. To make chromium pass the bot, it must be white listed

Bug: 786166
Change-Id: Ic578edc3b1d724fcee994f94dd3a0b19f67323a4
Reviewed-on: https://chromium-review.googlesource.com/776057
Commit-Queue: Gary Liu <qinghualiu@google.com>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517582}

chrome/test/data/webrtc/peerconnection_getstats.js

@@ -191,6 +191,7 @@ gStatsWhitelist.set('transport', kRTCTransportStats);
 var kRTCIceCandidateStats = new RTCStats_(null, {
   transportId: 'string',
   isRemote: 'boolean',
+  networkType: 'string',
   ip: 'string',
   port: 'number',
   protocol: 'string',