Update {virtual,override,final} to follow C++11 style in ash.

ash/system/chromeos/keyboard_brightness_controller.h

Index: ash/system/chromeos/keyboard_brightness_controller.h
diff --git a/ash/system/chromeos/keyboard_brightness_controller.h b/ash/system/chromeos/keyboard_brightness_controller.h
index 41878794211d10be60cc5f76124559e65b17cb23..bc3c79ef9517521ef1f0baf51aba27a448694ae5 100644
--- a/ash/system/chromeos/keyboard_brightness_controller.h
+++ b/ash/system/chromeos/keyboard_brightness_controller.h
@@ -18,14 +18,13 @@ class ASH_EXPORT KeyboardBrightnessController
     : public KeyboardBrightnessControlDelegate {
  public:
   KeyboardBrightnessController() {}
-  virtual ~KeyboardBrightnessController() {}
+  ~KeyboardBrightnessController() override {}
 
  private:
   // Overridden from KeyboardBrightnessControlDelegate:
-  virtual void HandleKeyboardBrightnessDown(
-      const ui::Accelerator& accelerator) override;
-  virtual void HandleKeyboardBrightnessUp(
+  void HandleKeyboardBrightnessDown(
       const ui::Accelerator& accelerator) override;
+  void HandleKeyboardBrightnessUp(const ui::Accelerator& accelerator) override;
 
   DISALLOW_COPY_AND_ASSIGN(KeyboardBrightnessController);
 };