Standardize usage of virtual/override/final specifiers.

media/midi/midi_manager_alsa.h

Index: media/midi/midi_manager_alsa.h
diff --git a/media/midi/midi_manager_alsa.h b/media/midi/midi_manager_alsa.h
index c59beefd67eb36597577c819ab51fcbc9efb83fb..cbe03c5fee776a69e1ec715e40a71a7edd936c1e 100644
--- a/media/midi/midi_manager_alsa.h
+++ b/media/midi/midi_manager_alsa.h
@@ -20,14 +20,14 @@ namespace media {
 class MidiManagerAlsa : public MidiManager {
  public:
   MidiManagerAlsa();
-  virtual ~MidiManagerAlsa();
+  ~MidiManagerAlsa() override;
 
   // MidiManager implementation.
-  virtual void StartInitialization() override;
-  virtual void DispatchSendMidiData(MidiManagerClient* client,
-                                    uint32 port_index,
-                                    const std::vector<uint8>& data,
-                                    double timestamp) override;
+  void StartInitialization() override;
+  void DispatchSendMidiData(MidiManagerClient* client,
+                            uint32 port_index,
+                            const std::vector<uint8>& data,
+                            double timestamp) override;
 
  private:
   // An internal callback that runs on MidiSendThread.