It was used only to break the circular dependency between SocketServer and Thread at destruction time. Replaced with a method call to SetMessageQueue(nullptr). Bug: webrtc:11943 Change-Id: I0606d473ad79655cca28411bb02c21e21d2d7220 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215587 Reviewed-by: Tommi <tommi@webrtc.org> Commit-Queue: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33807}