Standardize usage of virtual/override/final specifiers.

ash/desktop_background/desktop_background_widget_controller.h

Index: ash/desktop_background/desktop_background_widget_controller.h
diff --git a/ash/desktop_background/desktop_background_widget_controller.h b/ash/desktop_background/desktop_background_widget_controller.h
index 0aafe2ea473d991408dae588cc3160cdfc5a93a3..bad030c6fe0b32dfcfeceb6327853be474f8a32f 100644
--- a/ash/desktop_background/desktop_background_widget_controller.h
+++ b/ash/desktop_background/desktop_background_widget_controller.h
@@ -25,10 +25,10 @@ class ASH_EXPORT DesktopBackgroundWidgetController
   // Create
   explicit DesktopBackgroundWidgetController(views::Widget* widget);
 
-  virtual ~DesktopBackgroundWidgetController();
+  ~DesktopBackgroundWidgetController() override;
 
   // Overridden from views::WidgetObserver.
-  virtual void OnWidgetDestroying(views::Widget* widget) override;
+  void OnWidgetDestroying(views::Widget* widget) override;
 
   // Set bounds of component that draws background.
   void SetBounds(gfx::Rect bounds);