Add ability to export internal state of SamplesStatsCounter to be able
then to plot that data.
Bug: webrtc:10138
Change-Id: I5aae5b7dea2989e9f82820933a9ab6f21db17556
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/152542
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29173}