RTCIceCandidateStats.deleted = false added.

Since previously, only the deleted = false case is supported, but now
that stat is added. It's a recent addition to the spec:
https://w3c.github.io/webrtc-stats/#dom-rtcicecandidatestats-deleted

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

Review-Url: https://codereview.webrtc.org/2591963003
Cr-Original-Commit-Position: refs/heads/master@{#15871}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d17a5a7709fcef98bb6fcd0d2a99e11dfcc38bb7
4 files changed