Fix thread safety in VcmCapturer.

webrtc/test/vcm_capturer.h

Index: webrtc/test/vcm_capturer.h
diff --git a/webrtc/test/vcm_capturer.h b/webrtc/test/vcm_capturer.h
index 93321f0ff1465b5b2a2c1f8281fc1f15be4f639a..53d61fc53a27c188330be4ff98a8d4d06d4ec392 100644
--- a/webrtc/test/vcm_capturer.h
+++ b/webrtc/test/vcm_capturer.h
@@ -10,6 +10,7 @@
 #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"
@@ -38,7 +39,8 @@ class VcmCapturer : public VideoCapturer, public VideoCaptureDataCallback {
   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_;
 };