Ignore fullscreen windows which are behind other windows for fullscreen mode.

ash/root_window_controller.h

 // Copyright (c) 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_ROOT_WINDOW_CONTROLLER_H_
 #define ASH_ROOT_WINDOW_CONTROLLER_H_
 
 #include <map>
 
 #include "ash/ash_export.h"
@@ skipping 203 matching lines @@
 
   // Moves child windows to |dest|.
   void MoveWindowsTo(aura::Window* dest);
 
   // Force the shelf to query for it's current visibility state.
   void UpdateShelfVisibility();
 
   // Initialize touch HUDs if necessary.
   void InitTouchHuds();
 
-  // Returns the window, if any, which is in fullscreen mode. If multiple
-  // windows are in fullscreen state, the topmost one is preferred.
+  // Returns the topmost window or one of its transient parents, if any of them
+  // are in fullscreen mode.
   const aura::Window* GetTopmostFullscreenWindow() const;
   aura::Window* GetTopmostFullscreenWindow();
 
   // Activate virtual keyboard on current root window controller.
   void ActivateKeyboard(keyboard::KeyboardController* keyboard_controller);
 
   // Deactivate virtual keyboard on current root window controller.
   void DeactivateKeyboard(keyboard::KeyboardController* keyboard_controller);
 
  private:
@@ skipping 82 matching lines @@
 
 
 // Gets the RootWindowController for |root_window|.
 ASH_EXPORT RootWindowController* GetRootWindowController(
     const aura::Window* root_window);
 
 }  // namespace internal
 }  // ash
 
 #endif  //  ASH_ROOT_WINDOW_CONTROLLER_H_