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

ui/aura/window_types.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_WINDOW_TYPES_H_
+#define UI_AURA_WINDOW_TYPES_H_
+#pragma once
+
+namespace aura {
+
+const int kWindowType_Toplevel = 0;
+const int kWindowType_Control = 1;
+const int kWindowType_Menu = 2;
+const int kWindowType_Tooltip = 3;
+
+const int kWindowType_Max = 4;
+
+}  // namespace aura
+
+#endif  // UI_AURA_WINDOW_TYPES_H_