Fix thread safety in VcmCapturer.

webrtc/test/vcm_capturer.h

 /*
  *  Copyright (c) 2013 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.
  */
 #ifndef WEBRTC_VIDEO_ENGINE_TEST_COMMON_VCM_CAPTURER_H_
 #define WEBRTC_VIDEO_ENGINE_TEST_COMMON_VCM_CAPTURER_H_
 
+#include "webrtc/base/criticalsection.h"
 #include "webrtc/common_types.h"
 #include "webrtc/common_video/libyuv/include/webrtc_libyuv.h"
 #include "webrtc/modules/video_capture/include/video_capture.h"
 #include "webrtc/test/video_capturer.h"
 
 namespace webrtc {
 namespace test {
 
 class VcmCapturer : public VideoCapturer, public VideoCaptureDataCallback {
  public:
   static VcmCapturer* Create(VideoCaptureInput* input,
                              size_t width,
                              size_t height,
                              size_t target_fps);
   virtual ~VcmCapturer();
 
   void Start() override;
   void Stop() override;
 
   void OnIncomingCapturedFrame(const int32_t id,
                                const VideoFrame& frame) override;  // NOLINT
   void OnCaptureDelayChanged(const int32_t id, const int32_t delay) override;
 
  private:
   explicit VcmCapturer(VideoCaptureInput* input);
   bool Init(size_t width, size_t height, size_t target_fps);
   void Destroy();
 
-  bool started_;
+  rtc::CriticalSection crit_;
+  bool started_ GUARDED_BY(crit_);
   VideoCaptureModule* vcm_;
   VideoCaptureCapability capability_;
 };
 }  // test
 }  // webrtc
 
 #endif  // WEBRTC_VIDEO_ENGINE_TEST_COMMON_VCM_CAPTURER_H_