Overview Tray Button should not be visible on login screen

ash/system/overview/overview_button_tray.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_
 #define ASH_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_
 
 #include "ash/ash_export.h"
 #include "ash/shell_observer.h"
 #include "ash/system/tray/tray_background_view.h"
 
 namespace views {
 class ImageView;
 }
 
 namespace ash {
 
 // Status area tray for showing a toggle for Overview Mode. Overview Mode
 // is equivalent to WindowSelectorController being in selection mode.
 // This hosts a ShellObserver that listens for the activation of Maximize Mode
 // This tray will only be visible while in this state. This tray does not
 // provide any bubble view windows.
 class ASH_EXPORT OverviewButtonTray : public internal::TrayBackgroundView,
                                       public ShellObserver {
  public:
   explicit OverviewButtonTray(internal::StatusAreaWidget* status_area_widget);
   virtual ~OverviewButtonTray();
 
+  // Updates the tray's visibility based on the LoginStatus and the current
+  // state of MaximizeMode
+  virtual void UpdateAfterLoginStatusChange(user::LoginStatus status);
+
   // internal::ActionableView:
   virtual bool PerformAction(const ui::Event& event) OVERRIDE;
 
   // ShellObserver:
   virtual void OnMaximizeModeStarted() OVERRIDE;
   virtual void OnMaximizeModeEnded() OVERRIDE;
 
   // internal::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;
 
  private:
   friend class OverviewButtonTrayTest;
 
   // Creates a new border for the icon. The padding is determined based on the
   // alignment of the shelf.
   void SetIconBorderForShelfAlignment();
 
+  // Sets the icon to visible if |maximize_mode_enabled| and
+  // WindowSelectorController::CanSelect.
+  void UpdateIconVisibility(bool maximize_mode_enabled);
+
   // Weak pointer, will be parented by TrayContainer for its lifetime.
   views::ImageView* icon_;
 
   DISALLOW_COPY_AND_ASSIGN(OverviewButtonTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_