This is part of a CL series merging rtc::MessageQueue into rtc::Thread. Bug: webrtc:9883 Change-Id: I3cb857cc707d5e897759366d1478cc1ec19bce9a Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/165344 Reviewed-by: Stefan Holmer <stefan@webrtc.org> Commit-Queue: Sebastian Jansson <srte@webrtc.org> Cr-Commit-Position: refs/heads/master@{#30180}