Standardize usage of virtual/override/final in media/

media/midi/midi_manager_mac.h

Index: media/midi/midi_manager_mac.h
diff --git a/media/midi/midi_manager_mac.h b/media/midi/midi_manager_mac.h
index fbc594b502d84f74f77bd5427395a23f85167b06..f7179ec18a7494b3f1181481a59184053dc3d4f1 100644
--- a/media/midi/midi_manager_mac.h
+++ b/media/midi/midi_manager_mac.h
@@ -22,14 +22,14 @@ namespace media {
 class MEDIA_EXPORT MidiManagerMac : public MidiManager {
  public:
   MidiManagerMac();
-  virtual ~MidiManagerMac();
+  ~MidiManagerMac() 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:
   // Runs a closure on |client_thread_|. It starts the thread if it isn't