Moves management of transients out of Window

ui/views/corewm/transient_window_stacking_client.h

 // Copyright (c) 2013 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_VIEWS_COREWM_TRANSIENT_WINDOW_STACKING_CLIENT_H_
 #define UI_VIEWS_COREWM_TRANSIENT_WINDOW_STACKING_CLIENT_H_
 
 #include "ui/aura/client/window_stacking_client.h"
 #include "ui/views/views_export.h"
 
 namespace views {
 namespace corewm {
 
+class TransientWindowManager;
+
 class VIEWS_EXPORT TransientWindowStackingClient
     : public aura::client::WindowStackingClient {
  public:
   TransientWindowStackingClient();
   virtual ~TransientWindowStackingClient();
 
   // WindowStackingClient:
   virtual bool AdjustStacking(aura::Window** child,
                               aura::Window** target,
                               aura::Window::StackDirection* direction) OVERRIDE;
 
  private:
+  // Purely for DCHECKs.
+  friend class TransientWindowManager;
+
+  static TransientWindowStackingClient* instance_;
+
   DISALLOW_COPY_AND_ASSIGN(TransientWindowStackingClient);
 };
 
 }  // namespace corewm
 }  // namespace views
 
 #endif  // UI_VIEWS_COREWM_TRANSIENT_WINDOW_STACKING_CLIENT_H_