Overview Tray Button should not be visible on login screen

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 0a16e4781f99bb90ae337634bc2561e9b498e91b..0e1d97c01d6719c436857da90815629b00364e87 100644
--- a/ash/system/overview/overview_button_tray.h
+++ b/ash/system/overview/overview_button_tray.h
@@ -40,6 +40,10 @@ class ASH_EXPORT OverviewButtonTray : public internal::TrayBackgroundView,
       const views::TrayBubbleView* bubble_view) OVERRIDE;
   virtual void SetShelfAlignment(ShelfAlignment alignment) OVERRIDE;
 
+  // Updates the tray's visibility based on the LoginStatus and the current
+  // state of MaximizeMode
+  virtual void UpdateAfterLoginStatusChange(user::LoginStatus status);
+
  private:
   friend class OverviewButtonTrayTest;
 
@@ -47,6 +51,10 @@ class ASH_EXPORT OverviewButtonTray : public internal::TrayBackgroundView,
   // alignment of the shelf.
   void SetIconBorderForShelfAlignment();
 
+  // Sets the icon to visible if |maximize_mode_enabled| and
+  // WindowSelectorController::CanSelect.
+  void SetIconVisibility(bool maximize_mode_enabled);
+
   // Weak pointer, will be parented by TrayContainer for its lifetime.
   views::ImageView* icon_;