Fix occasional race in VideoCapturerTrackSource seen by memcheck bot.

webrtc/pc/videocapturertracksource.h

 /*
  *  Copyright 2012 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 29 matching lines @@
       rtc::Thread* worker_thread,
       std::unique_ptr<cricket::VideoCapturer> capturer,
       const webrtc::MediaConstraintsInterface* constraints,
       bool remote);
 
   static rtc::scoped_refptr<VideoTrackSourceInterface> Create(
       rtc::Thread* worker_thread,
       std::unique_ptr<cricket::VideoCapturer> capturer,
       bool remote);
 
-  bool is_screencast() const override {
-    return video_capturer_->IsScreencast();
-  }
-  rtc::Optional<bool> needs_denoising() const override {
-    return needs_denoising_;
-  }
+  bool is_screencast() const final { return video_capturer_->IsScreencast(); }
+  rtc::Optional<bool> needs_denoising() const final { return needs_denoising_; }
 
-  bool GetStats(Stats* stats) override;
+  bool GetStats(Stats* stats) final;
 
  protected:
   VideoCapturerTrackSource(rtc::Thread* worker_thread,
                            std::unique_ptr<cricket::VideoCapturer> capturer,
                            bool remote);
   virtual ~VideoCapturerTrackSource();
   void Initialize(const webrtc::MediaConstraintsInterface* constraints);
 
  private:
   void Stop();
 
   void OnStateChange(cricket::VideoCapturer* capturer,
                      cricket::CaptureState capture_state);
 
   rtc::Thread* signaling_thread_;
   rtc::Thread* worker_thread_;
   rtc::AsyncInvoker invoker_;
   std::unique_ptr<cricket::VideoCapturer> video_capturer_;
   bool started_;
   cricket::VideoFormat format_;
   rtc::Optional<bool> needs_denoising_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_PC_VIDEOCAPTURERTRACKSOURCE_H_