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

webrtc/base/thread.cc

Index: webrtc/base/thread.cc
diff --git a/webrtc/base/thread.cc b/webrtc/base/thread.cc
index c6dc3c45a03c9a37bd183ae3e82df01fd55c9369..07e42f86c11fed90eacdba3526dbf5a075b52b0d 100644
--- a/webrtc/base/thread.cc
+++ b/webrtc/base/thread.cc
@@ -219,7 +219,7 @@ bool Thread::Start(Runnable* runnable) {
   ASSERT(!running());
   if (running()) return false;
 
-  Restart();  // reset fStop_ if the thread is being restarted
+  Restart();  // reset IsQuitting() if the thread is being restarted
 
   // Make sure that ThreadManager is created on the main thread before
   // we start a new thread.
@@ -344,7 +344,7 @@ void Thread::Stop() {
 }
 
 void Thread::Send(MessageHandler* phandler, uint32_t id, MessageData* pdata) {
-  if (fStop_)
+  if (IsQuitting())
     return;
 
   // Sent messages are sent to the MessageHandler directly, in the context