Standardize usage of virtual/override/final specifiers.

media/audio/alsa/alsa_output.h

Index: media/audio/alsa/alsa_output.h
diff --git a/media/audio/alsa/alsa_output.h b/media/audio/alsa/alsa_output.h
index dfc044d6e964c80902a925a6dae22e7e8b7c1834..fd0910a50b72b52d912b2c1b7831eb09dbf29c80 100644
--- a/media/audio/alsa/alsa_output.h
+++ b/media/audio/alsa/alsa_output.h
@@ -72,15 +72,15 @@ class MEDIA_EXPORT AlsaPcmOutputStream : public AudioOutputStream {
                       AlsaWrapper* wrapper,
                       AudioManagerBase* manager);
 
-  virtual ~AlsaPcmOutputStream();
+  ~AlsaPcmOutputStream() override;
 
   // Implementation of AudioOutputStream.
-  virtual bool Open() override;
-  virtual void Close() override;
-  virtual void Start(AudioSourceCallback* callback) override;
-  virtual void Stop() override;
-  virtual void SetVolume(double volume) override;
-  virtual void GetVolume(double* volume) override;
+  bool Open() override;
+  void Close() override;
+  void Start(AudioSourceCallback* callback) override;
+  void Stop() override;
+  void SetVolume(double volume) override;
+  void GetVolume(double* volume) override;
 
  private:
   friend class AlsaPcmOutputStreamTest;