Add AEC filter divergence metric to StatsCollector.

A new metric that tells how often the AEC linear filter diverges has been recently introduced, see
https://codereview.webrtc.org/1739993003/

This metric can reflect echo failure and ducking.

In this CL, we add a field in StatsCollector to receive this metric.

BUG=
R=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1866983002 .

Cr-Original-Commit-Position: refs/heads/master@{#12282}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 2a8a78c905a68935d2ff53355982601e2e083dfa
4 files changed