Standardize usage of virtual/override/final specifiers.

ash/wm/system_background_controller.h

Index: ash/wm/system_background_controller.h
diff --git a/ash/wm/system_background_controller.h b/ash/wm/system_background_controller.h
index 41e7c98708758dc4da9d274577651f78e6154e32..c695cbdf26ab8e12e25d010f6871d05391f56cb8 100644
--- a/ash/wm/system_background_controller.h
+++ b/ash/wm/system_background_controller.h
@@ -28,14 +28,14 @@ namespace ash {
 class SystemBackgroundController : public aura::WindowObserver {
  public:
   SystemBackgroundController(aura::Window* root_window, SkColor color);
-  virtual ~SystemBackgroundController();
+  ~SystemBackgroundController() override;
 
   void SetColor(SkColor color);
 
   // aura::WindowObserver overrides:
-  virtual void OnWindowBoundsChanged(aura::Window* root,
-                                     const gfx::Rect& old_bounds,
-                                     const gfx::Rect& new_bounds) override;
+  void OnWindowBoundsChanged(aura::Window* root,
+                             const gfx::Rect& old_bounds,
+                             const gfx::Rect& new_bounds) override;
 
  private:
   class HostContentLayerDelegate;