Fix chromium-style warnings in webrtc/sound/.

webrtc/sound/platformsoundsystemfactory.h

Index: webrtc/sound/platformsoundsystemfactory.h
diff --git a/webrtc/sound/platformsoundsystemfactory.h b/webrtc/sound/platformsoundsystemfactory.h
index c5105ef051310fd785b66438bfa67db9e612a6a6..5319fa50b60d7d0f498a49ce57c9a1236a217ec3 100644
--- a/webrtc/sound/platformsoundsystemfactory.h
+++ b/webrtc/sound/platformsoundsystemfactory.h
@@ -20,16 +20,14 @@ namespace rtc {
 class PlatformSoundSystemFactory : public SoundSystemFactory {
  public:
   PlatformSoundSystemFactory();
-  virtual ~PlatformSoundSystemFactory();
+  ~PlatformSoundSystemFactory() override;
 
  protected:
   // Inherited from SoundSystemFactory.
-  virtual bool SetupInstance();
-  virtual void CleanupInstance();
+  bool SetupInstance() override;
+  void CleanupInstance() override;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_SOUND_PLATFORMSOUNDSYSTEMFACTORY_H_
-
-