Standardize usage of virtual/override/final specifiers.

ash/high_contrast/high_contrast_controller.h

Index: ash/high_contrast/high_contrast_controller.h
diff --git a/ash/high_contrast/high_contrast_controller.h b/ash/high_contrast/high_contrast_controller.h
index 84752170bc1396a5faef7a34b1032b2549b9294c..313aa0566662a0a8b4f47b10d81ed2309cd314d1 100644
--- a/ash/high_contrast/high_contrast_controller.h
+++ b/ash/high_contrast/high_contrast_controller.h
@@ -18,13 +18,13 @@ namespace ash {
 class ASH_EXPORT HighContrastController : public ShellObserver {
  public:
   HighContrastController();
-  virtual ~HighContrastController();
+  ~HighContrastController() override;
 
   // Set high contrast mode and update all available displays.
   void SetEnabled(bool enabled);
 
   // ShellObserver:
-  virtual void OnRootWindowAdded(aura::Window* root_window) override;
+  void OnRootWindowAdded(aura::Window* root_window) override;
 
  private:
   // Update high contrast mode on the passed display.