Fix race between Thread ctor/dtor and MessageQueueManager registrations.

webrtc/base/thread.h

Index: webrtc/base/thread.h
diff --git a/webrtc/base/thread.h b/webrtc/base/thread.h
index f91aa56733cb82a880adf6c35ae43114c712fe07..f03bf3839275948876f4867d12622eabe18a1a2c 100644
--- a/webrtc/base/thread.h
+++ b/webrtc/base/thread.h
@@ -297,7 +297,7 @@ class AutoThread : public Thread {
 class ComThread : public Thread {
  public:
   ComThread() {}
-  virtual ~ComThread() { Stop(); }
+  ~ComThread() override;
 
  protected:
   virtual void Run();