Show overview mode button in TouchView with open modal window

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"
@@ skipping 34 matching lines @@
   void HideBubbleWithView(const views::TrayBubbleView* bubble_view) override;
   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 is enabled and
-  // WindowSelectorController::CanSelect.
+  // Shows or hides the overview button. The button should be shown when the
+  // user is in maximize mode and is in an active desktop environment, otherwise
+  // the button should be hidden.
   void UpdateIconVisibility();
 
   // 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_