Disallow toggling of shelf auto-hide with touch when there are no windows open

ash/shelf/shelf_layout_manager.h

 // Copyright 2012 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_SHELF_SHELF_LAYOUT_MANAGER_H_
 #define ASH_SHELF_SHELF_LAYOUT_MANAGER_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 243 matching lines @@
   // Stops the auto hide timer and clears
   // |mouse_over_shelf_when_auto_hide_timer_started_|.
   void StopAutoHideTimer();
 
   // Returns the bounds of an additional region which can trigger showing the
   // shelf. This region exists to make it easier to trigger showing the shelf
   // when the shelf is auto hidden and the shelf is on the boundary between
   // two displays.
   gfx::Rect GetAutoHideShowShelfRegionInScreen() const;
 
+  // Returns true if at least one window is visible.
+  bool HasVisibleWindow() const;
+
   // Returns the AutoHideState. This value is determined from the shelf and
   // tray.
   ShelfAutoHideState CalculateAutoHideState(
       ShelfVisibilityState visibility_state) const;
 
   // Returns true if |window| is a descendant of the shelf.
   bool IsShelfWindow(WmWindow* window);
 
   int GetWorkAreaInsets(const State& state, int size) const;
 
@@ skipping 86 matching lines @@
   ScopedObserver<keyboard::KeyboardController,
                  keyboard::KeyboardControllerObserver>
       keyboard_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfLayoutManager);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_LAYOUT_MANAGER_H_