Standardize usage of virtual/override/final specifiers.

ash/system/overview/overview_button_tray.h

Index: ash/system/overview/overview_button_tray.h
diff --git a/ash/system/overview/overview_button_tray.h b/ash/system/overview/overview_button_tray.h
index 94d9099b2751a8dd066043f80d56be024058a98d..1aca24a93af144de16c27e395d5f18bbc0462c92 100644
--- a/ash/system/overview/overview_button_tray.h
+++ b/ash/system/overview/overview_button_tray.h
@@ -25,26 +25,25 @@ class ASH_EXPORT OverviewButtonTray : public TrayBackgroundView,
                                       public ShellObserver {
  public:
   explicit OverviewButtonTray(StatusAreaWidget* status_area_widget);
-  virtual ~OverviewButtonTray();
+  ~OverviewButtonTray() override;
 
   // Updates the tray's visibility based on the LoginStatus and the current
   // state of MaximizeMode
   virtual void UpdateAfterLoginStatusChange(user::LoginStatus status);
 
   // ActionableView:
-  virtual bool PerformAction(const ui::Event& event) override;
+  bool PerformAction(const ui::Event& event) override;
 
   // ShellObserver:
-  virtual void OnMaximizeModeStarted() override;
-  virtual void OnMaximizeModeEnded() override;
-  virtual void OnOverviewModeEnding() override;
+  void OnMaximizeModeStarted() override;
+  void OnMaximizeModeEnded() override;
+  void OnOverviewModeEnding() override;
 
   // TrayBackgroundView:
-  virtual bool ClickedOutsideBubble() override;
-  virtual base::string16 GetAccessibleNameForTray() override;
-  virtual void HideBubbleWithView(
-      const views::TrayBubbleView* bubble_view) override;
-  virtual void SetShelfAlignment(ShelfAlignment alignment) override;
+  bool ClickedOutsideBubble() override;
+  base::string16 GetAccessibleNameForTray() override;
+  void HideBubbleWithView(const views::TrayBubbleView* bubble_view) override;
+  void SetShelfAlignment(ShelfAlignment alignment) override;
 
  private:
   friend class OverviewButtonTrayTest;