[getStats] Whitelist headerBytesSent and headerBytesReceived.

This unblocks https://webrtc-review.googlesource.com/c/src/+/156084.

TBR=nisse@chromium.org
NOTRY=True

Bug: webrtc:10525
Change-Id: I9ca14f4c5c6d38b8a71b77c2393e842f2e6966c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1862437Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705875}

chrome/test/data/webrtc/peerconnection_getstats.js

@@ -124,6 +124,7 @@ let kRTCInboundRtpStreamStats = new RTCStats(kRTCReceivedRtpStreamStats, {
   fecPacketsReceived: 'number',
   fecPacketsDiscarded: 'number',
   bytesReceived: 'number',
+  headerBytesReceived: 'number',
   packetsFailedDecryption: 'number',
   packetsDuplicated: 'number',
   perDscpPacketsReceived: 'object',
@@ -180,6 +181,7 @@ let kRTCOutboundRtpStreamStats = new RTCStats(kRTCSentRtpStreamStats, {
   lastPacketSentTimestamp: 'number',
   retransmittedPacketsSent: 'number',
   retransmittedBytesSent: 'number',
+  headerBytesSent: 'number',
   targetBitrate: 'number',
   totalEncodedBytesTarget: 'number',
   framesEncoded: 'number',