Protect MessageQueue stop field with a critical section to avoid data races.

webrtc/base/messagequeue.h

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 270 matching lines @@
   // Perform initialization, subclasses must call this from their constructor
   // if false was passed as init_queue to the MessageQueue constructor.
   void DoInit();
 
   // Perform cleanup, subclasses that override Clear must call this from the
   // destructor.
   void DoDestroy();
 
   void WakeUpSocketServer();
 
-  bool fStop_;
   bool fPeekKeep_;
   Message msgPeek_;
   MessageList msgq_ GUARDED_BY(crit_);
   PriorityQueue dmsgq_ GUARDED_BY(crit_);
   uint32_t dmsgq_next_num_ GUARDED_BY(crit_);
   CriticalSection crit_;
   bool fInitialized_;
   bool fDestroyed_;
 
  private:
+  volatile int stop_;
+
   // The SocketServer might not be owned by MessageQueue.
   SocketServer* ss_ GUARDED_BY(ss_lock_);
   // Used if SocketServer ownership lies with |this|.
   std::unique_ptr<SocketServer> own_ss_;
   SharedExclusiveLock ss_lock_;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(MessageQueue);
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_MESSAGEQUEUE_H_