Remove mutable from rtc::CriticalSection members.

webrtc/base/bufferqueue.h

Index: webrtc/base/bufferqueue.h
diff --git a/webrtc/base/bufferqueue.h b/webrtc/base/bufferqueue.h
index 458f0189cdbe541301cbd9e5bacacdd953a67db7..89ffdf01892d9d6d25c550872d21c21b514a44b3 100644
--- a/webrtc/base/bufferqueue.h
+++ b/webrtc/base/bufferqueue.h
@@ -45,7 +45,7 @@ class BufferQueue {
  private:
   size_t capacity_;
   size_t default_size_;
-  mutable CriticalSection crit_;
+  CriticalSection crit_;
   std::deque<Buffer*> queue_ GUARDED_BY(crit_);
   std::vector<Buffer*> free_list_ GUARDED_BY(crit_);