Fix chromium-style warnings in webrtc/sound/.

webrtc/sound/nullsoundsystem.h

Index: webrtc/sound/nullsoundsystem.h
diff --git a/webrtc/sound/nullsoundsystem.h b/webrtc/sound/nullsoundsystem.h
index 6b749976650f6ad7b28d33ae758b8c5cebdde536..08ffad1015e2bf707bb02e46486f5c18ba23f04e 100644
--- a/webrtc/sound/nullsoundsystem.h
+++ b/webrtc/sound/nullsoundsystem.h
@@ -27,25 +27,25 @@ class NullSoundSystem : public SoundSystemInterface {
     return new NullSoundSystem();
   }
 
-  virtual ~NullSoundSystem();
+  ~NullSoundSystem() override;
 
-  virtual bool Init();
-  virtual void Terminate();
+  bool Init() override;
+  void Terminate() override;
 
-  virtual bool EnumeratePlaybackDevices(SoundDeviceLocatorList *devices);
-  virtual bool EnumerateCaptureDevices(SoundDeviceLocatorList *devices);
+  bool EnumeratePlaybackDevices(SoundDeviceLocatorList *devices) override;
+  bool EnumerateCaptureDevices(SoundDeviceLocatorList *devices) override;
 
-  virtual SoundOutputStreamInterface *OpenPlaybackDevice(
+  SoundOutputStreamInterface *OpenPlaybackDevice(
       const SoundDeviceLocator *device,
-      const OpenParams &params);
-  virtual SoundInputStreamInterface *OpenCaptureDevice(
+      const OpenParams &params) override;
+  SoundInputStreamInterface *OpenCaptureDevice(
       const SoundDeviceLocator *device,
-      const OpenParams &params);
+      const OpenParams &params) override;
 
-  virtual bool GetDefaultPlaybackDevice(SoundDeviceLocator **device);
-  virtual bool GetDefaultCaptureDevice(SoundDeviceLocator **device);
+  bool GetDefaultPlaybackDevice(SoundDeviceLocator **device) override;
+  bool GetDefaultCaptureDevice(SoundDeviceLocator **device) override;
 
-  virtual const char *GetName() const;
+  const char *GetName() const override;
 };
 
 }  // namespace rtc