Add * and / operator into SamplesStatsCounter to simplify convertion between samples units. Bug: webrtc:10138 Change-Id: I985b60bc63c071ceaf0fddcdbcd3e6476353c0fe Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/142171 Commit-Queue: Artem Titov <titovartem@webrtc.org> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org> Cr-Commit-Position: refs/heads/master@{#28456}