Standardize usage of virtual/override/final specifiers.

ash/desktop_background/desktop_background_view.cc

Index: ash/desktop_background/desktop_background_view.cc
diff --git a/ash/desktop_background/desktop_background_view.cc b/ash/desktop_background/desktop_background_view.cc
index 3af8599fda938155b9b21778bca9d917098e001c..c87b4fde348ea3a1889fda8a3f0f78f61f3ce563 100644
--- a/ash/desktop_background/desktop_background_view.cc
+++ b/ash/desktop_background/desktop_background_view.cc
@@ -49,7 +49,7 @@ class LayerControlView : public views::View {
   }
 
   // Overrides views::View.
-  virtual void Layout() override {
+  void Layout() override {
     gfx::Display display = Shell::GetScreen()->GetDisplayNearestWindow(
         GetWidget()->GetNativeView());
     DisplayManager* display_manager = Shell::GetInstance()->display_manager();
@@ -79,11 +79,11 @@ class LayerControlView : public views::View {
 class PreEventDispatchHandler : public ui::EventHandler {
  public:
   PreEventDispatchHandler() {}
-  virtual ~PreEventDispatchHandler() {}
+  ~PreEventDispatchHandler() override {}
 
  private:
   // ui::EventHandler:
-  virtual void OnMouseEvent(ui::MouseEvent* event) override {
+  void OnMouseEvent(ui::MouseEvent* event) override {
     CHECK_EQ(ui::EP_PRETARGET, event->phase());
     WindowSelectorController* controller =
         Shell::GetInstance()->window_selector_controller();
@@ -93,7 +93,7 @@ class PreEventDispatchHandler : public ui::EventHandler {
     }
   }
 
-  virtual void OnGestureEvent(ui::GestureEvent* event) override {
+  void OnGestureEvent(ui::GestureEvent* event) override {
     CHECK_EQ(ui::EP_PRETARGET, event->phase());
     WindowSelectorController* controller =
         Shell::GetInstance()->window_selector_controller();