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

ui/aura/toplevel_window_container.h

Index: ui/aura/toplevel_window_container.h
===================================================================
--- ui/aura/toplevel_window_container.h	(revision 104542)
+++ ui/aura/toplevel_window_container.h	(working copy)
@@ -10,24 +10,25 @@
 #include "ui/aura/aura_export.h"
 
 namespace aura {
-namespace internal {
 
-class FocusManager;
-
 // A Window subclass that groups top-level windows.
 class AURA_EXPORT ToplevelWindowContainer : public Window {
  public:
   ToplevelWindowContainer();
   virtual ~ToplevelWindowContainer();
 
+  // Returns the topmost window to activate, ignoring |ignore|.
+  Window* GetTopmostWindowToActivate(Window* ignore) const;
+
   // Overridden from Window:
-  virtual bool IsToplevelWindowContainer() const OVERRIDE;
+  virtual ToplevelWindowContainer* AsToplevelWindowContainer() OVERRIDE;
+  virtual const ToplevelWindowContainer* AsToplevelWindowContainer() const
+      OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ToplevelWindowContainer);
 };
 
-}  // namespace internal
 }  // namespace aura
 
 #endif  // UI_AURA_TOPLEVEL_WINDOW_CONTAINER_H_