change the way windows are parented when their parent is set to NULL.

ui/aura_shell/shell_window_ids.h

 // Copyright (c) 2011 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 UI_AURA_SHELL_SHELL_WINDOW_IDS_H_
 #define UI_AURA_SHELL_SHELL_WINDOW_IDS_H_
 #pragma once
 
 // Declarations of ids of special shell windows.
 
@@ skipping 12 matching lines @@
 
 // The container for the launcher.
 const int kShellWindowId_LauncherContainer = 3;
 
 // The container for the lock screen.
 const int kShellWindowId_LockScreenContainer = 4;
 
 // The container for the status area.
 const int kShellWindowId_StatusContainer = 5;
 
+// The container for menus and tooltips.
+const int kShellWindowId_MenusAndTooltipsContainer = 6;
+
 }  // namespace internal
 
 }  // namespace aura_shell
 
 
 #endif  // UI_AURA_SHELL_SHELL_WINDOW_IDS_H_