Remove mutable from rtc::CriticalSection members.

webrtc/base/bufferqueue.h

 /*
  *  Copyright 2015 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 27 matching lines @@
   bool WriteBack(const void* data, size_t bytes, size_t* bytes_written);
 
  protected:
   // These methods are called when the state of the queue changes.
   virtual void NotifyReadableForTest() {}
   virtual void NotifyWritableForTest() {}
 
  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_);
 
   RTC_DISALLOW_COPY_AND_ASSIGN(BufferQueue);
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_BUFFERQUEUE_H_