Enable -Winconsistent-missing-override flag.

webrtc/api/videotrack.h

Index: webrtc/api/videotrack.h
diff --git a/webrtc/api/videotrack.h b/webrtc/api/videotrack.h
index 2f875321c1ad134fe7184622619a1820c4b96610..60a0a64aec7388a5eea571b89bb17ebb345d9613 100644
--- a/webrtc/api/videotrack.h
+++ b/webrtc/api/videotrack.h
@@ -33,11 +33,11 @@ class VideoTrack : public MediaStreamTrack<VideoTrackInterface>,
                        const rtc::VideoSinkWants& wants) override;
   void RemoveSink(rtc::VideoSinkInterface<cricket::VideoFrame>* sink) override;
 
-  virtual VideoTrackSourceInterface* GetSource() const {
+  VideoTrackSourceInterface* GetSource() const override {
     return video_source_.get();
   }
-  virtual bool set_enabled(bool enable);
-  virtual std::string kind() const;
+  bool set_enabled(bool enable) override;
+  std::string kind() const override;
 
  protected:
   VideoTrack(const std::string& id, VideoTrackSourceInterface* video_source);