Extract collection of BWE stats from DefaultVideoQualityAnalyzer to
separate class to prepare for migration on new GetStats API and simplify
quality analyzer.
Bug: webrtc:11381
Change-Id: I0e7e2d7e40b467d7a42633a72a7ffc49ebcb0237
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169444
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30650}