Remove mutable from rtc::CriticalSection members.

webrtc/modules/video_processing/video_processing_impl.h

 /*
  *  Copyright (c) 2011 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 26 matching lines @@
                               uint32_t frame_rate) override;
   void SetTargetFramerate(int frame_rate) override;
   uint32_t GetDecimatedFrameRate() override;
   uint32_t GetDecimatedWidth() const override;
   uint32_t GetDecimatedHeight() const override;
   void EnableDenosing(bool enable) override;
   const VideoFrame* PreprocessFrame(const VideoFrame& frame) override;
   VideoContentMetrics* GetContentMetrics() const override;
 
  private:
-  mutable rtc::CriticalSection mutex_;
+  rtc::CriticalSection mutex_;
   VPMDeflickering deflickering_ GUARDED_BY(mutex_);
   VPMBrightnessDetection brightness_detection_;
   VPMFramePreprocessor frame_pre_processor_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_PROCESSING_VIDEO_PROCESSING_IMPL_H_