State and priority added to ConnectionInfo. The Connection::State enum
is replaced by IceCandidatePairState enum class.
At P2PTransportChannel::GetStats, Connection::stats is called, producing
ConnectionInfo for the connection that is then filled in with additional
values from the Connection. This is refactored so that all values are
set by Connection::stats.
RTCStatsCollector is updated to surface the ConnectionInfo stats.
BUG=webrtc:6755, chromium:633550, chromium:627816
Review-Url: https://codereview.webrtc.org/2597423003
Cr-Commit-Position: refs/heads/master@{#15870}
06495bcbb7