Measure packet loss so we can use it to select ICE candidate pairs.

BUG=webrtc:7028

Review-Url: https://codereview.webrtc.org/2722933002
Cr-Original-Commit-Position: refs/heads/master@{#17313}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: abbacbf4892b98d77a53d2a5a5ed58d2162afdc6
6 files changed