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

ui/aura/desktop_delegate.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_DESKTOP_DELEGATE_H_
+#define UI_AURA_DESKTOP_DELEGATE_H_
+#pragma once
+
+namespace aura {
+
+class Window;
+
+class DesktopDelegate {
+ public:
+  // Called by the Window when its parent is set to NULL. The delegate is given
+  // an opportunity to inspect the window and add it to a default parent window
+  // of its choosing.
+  virtual void AddChildToDefaultParent(Window* window) = 0;
+
+  // Returns the window that should be activated other than |ignore|.
+  virtual Window* GetTopmostWindowToActivate(Window* ignore) const = 0;
+
+ protected:
+  virtual ~DesktopDelegate() {}
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_DESKTOP_DELEGATE_H_