Standardize usage of virtual/override/final specifiers.

ash/system/tray/tray_popup_item_container.h

Index: ash/system/tray/tray_popup_item_container.h
diff --git a/ash/system/tray/tray_popup_item_container.h b/ash/system/tray/tray_popup_item_container.h
index 8992b2161dd6b855032f3576a0e8cc1d767f3b3f..3771b5c976e5f85401989f8fb1183b31cf785b63 100644
--- a/ash/system/tray/tray_popup_item_container.h
+++ b/ash/system/tray/tray_popup_item_container.h
@@ -17,7 +17,7 @@ class TrayPopupItemContainer : public views::View {
                          bool change_background,
                          bool draw_border);
 
-  virtual ~TrayPopupItemContainer();
+  ~TrayPopupItemContainer() override;
 
   bool active() {
     return active_;
@@ -28,12 +28,12 @@ class TrayPopupItemContainer : public views::View {
   void SetActive(bool active);
 
   // views::View:
-  virtual void ChildVisibilityChanged(views::View* child) override;
-  virtual void ChildPreferredSizeChanged(views::View* child) override;
-  virtual void OnMouseEntered(const ui::MouseEvent& event) override;
-  virtual void OnMouseExited(const ui::MouseEvent& event) override;
-  virtual void OnGestureEvent(ui::GestureEvent* event) override;
-  virtual void OnPaintBackground(gfx::Canvas* canvas) override;
+  void ChildVisibilityChanged(views::View* child) override;
+  void ChildPreferredSizeChanged(views::View* child) override;
+  void OnMouseEntered(const ui::MouseEvent& event) override;
+  void OnMouseExited(const ui::MouseEvent& event) override;
+  void OnGestureEvent(ui::GestureEvent* event) override;
+  void OnPaintBackground(gfx::Canvas* canvas) override;
 
   // True if either a mouse is hovering over this view, or if a user has touched
   // down.