Standardize usage of virtual/override/final specifiers.

ash/system/date/date_default_view.h

Index: ash/system/date/date_default_view.h
diff --git a/ash/system/date/date_default_view.h b/ash/system/date/date_default_view.h
index fce0174decd7bcec6955e37ef815df473700a432..0a7d43d883d70ccd7435b607fbd9844e27afac7d 100644
--- a/ash/system/date/date_default_view.h
+++ b/ash/system/date/date_default_view.h
@@ -23,7 +23,7 @@ class ASH_EXPORT DateDefaultView : public views::View,
  public:
   explicit DateDefaultView(ash::user::LoginStatus login);
 
-  virtual ~DateDefaultView();
+  ~DateDefaultView() override;
 
   views::View* GetHelpButtonView();
 
@@ -32,8 +32,7 @@ class ASH_EXPORT DateDefaultView : public views::View,
 
  private:
   // Overridden from views::ButtonListener.
-  virtual void ButtonPressed(views::Button* sender,
-                             const ui::Event& event) override;
+  void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
   TrayPopupHeaderButton* help_;
   TrayPopupHeaderButton* shutdown_;