This makes it easier to maintain consistency between real time and simulated time modes. The RealTimeController is updated to use an explicit main thread, this ensures that pending destruction tasks are run as the network emulator goes out of scope. Bug: webrtc:11255 Change-Id: Ie73ab778c78a68d7c58c0f857f14a8d8ac027c67 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/166164 Commit-Queue: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Steve Anton <steveanton@webrtc.org> Reviewed-by: Artem Titov <titovartem@webrtc.org> Cr-Commit-Position: refs/heads/master@{#30342}