Standardize usage of virtual/override/final specifiers.

ash/desktop_background/desktop_background_view.h

Index: ash/desktop_background/desktop_background_view.h
diff --git a/ash/desktop_background/desktop_background_view.h b/ash/desktop_background/desktop_background_view.h
index 6a9382351fd50dce61dc84360fc918eb9ecd7077..17814d078fc8c04aace01f6a109301d1478170c5 100644
--- a/ash/desktop_background/desktop_background_view.h
+++ b/ash/desktop_background/desktop_background_view.h
@@ -18,17 +18,17 @@ class DesktopBackgroundView : public views::View,
                               public views::ContextMenuController {
  public:
   DesktopBackgroundView();
-  virtual ~DesktopBackgroundView();
+  ~DesktopBackgroundView() override;
 
  private:
   // Overridden from views::View:
-  virtual void OnPaint(gfx::Canvas* canvas) override;
-  virtual bool OnMousePressed(const ui::MouseEvent& event) override;
+  void OnPaint(gfx::Canvas* canvas) override;
+  bool OnMousePressed(const ui::MouseEvent& event) override;
 
   // Overridden from views::ContextMenuController:
-  virtual void ShowContextMenuForView(views::View* source,
-                                      const gfx::Point& point,
-                                      ui::MenuSourceType source_type) override;
+  void ShowContextMenuForView(views::View* source,
+                              const gfx::Point& point,
+                              ui::MenuSourceType source_type) override;
   scoped_ptr<PreEventDispatchHandler> pre_dispatch_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundView);