Support re-entrant calls to MessageQueueManager::Clear.

webrtc/rtc_base/messagequeue.h

Index: webrtc/rtc_base/messagequeue.h
diff --git a/webrtc/rtc_base/messagequeue.h b/webrtc/rtc_base/messagequeue.h
index d4057cd2df791dd6c8180aeb2f9788432aad06dd..0d0654e2ecaa8bc5ba8c5b00aab72390da1ed469 100644
--- a/webrtc/rtc_base/messagequeue.h
+++ b/webrtc/rtc_base/messagequeue.h
@@ -70,9 +70,11 @@ class MessageQueueManager {
   // This list contains all live MessageQueues.
   std::vector<MessageQueue*> message_queues_ GUARDED_BY(crit_);
 
-  // Acquire this with DebugNonReentrantCritScope.
+  // Methods that don't modify the list of message queues may be called in a
+  // re-entrant fashion. "processing_" keeps track of the depth of re-entrant
+  // calls.
   CriticalSection crit_;
-  bool locked_ GUARDED_BY(crit_);
+  size_t processing_ GUARDED_BY(crit_);
 };
 
 // Derive from this for specialized data