Since WebRTC stats are collected on the signaling thread, this CL moves the wait from the signaling thread to the main thread. Bug: webrtc:10138 Change-Id: I0e554fe82e3a4afe66b45e53032b06d533f54a39 Reviewed-on: https://webrtc-review.googlesource.com/c/123228 Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org> Reviewed-by: Artem Titov <titovartem@webrtc.org> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org> Cr-Commit-Position: refs/heads/master@{#26746}