RTCIceCandidateStats.isRemote added and collected.

This was added to the spec: https://w3c.github.io/webrtc-stats/#dom-rtcicecandidatestats-isremote

BUG=webrtc:6756, chromium:632723, chromium:627816

Review-Url: https://codereview.webrtc.org/2595003003
Cr-Original-Commit-Position: refs/heads/master@{#15863}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c3a2b7f4877b09357ab453f698451bdb75c7bc1c