Moves TransientWindowClient to ui/aura/client and adds observer

ui/aura/client/transient_window_client.h

 // Copyright 2014 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_WM_PUBLIC_TRANSIENT_WINDOW_CLIENT_H_
-#define UI_WM_PUBLIC_TRANSIENT_WINDOW_CLIENT_H_
+#ifndef UI_AURA_CLIENT_TRANSIENT_WINDOW_CLIENT_H_
+#define UI_AURA_CLIENT_TRANSIENT_WINDOW_CLIENT_H_
 
 #include "ui/aura/aura_export.h"
 
 namespace aura {
 
 class Window;
 
 namespace client {
 
+class TransientWindowClientObserver;
+
 // TransientWindowClient is used to add or remove transient windows. Transient
 // children get the following behavior:
 // . The transient parent destroys any transient children when it is
 //   destroyed. This means a transient child is destroyed if either its parent
 //   or transient parent is destroyed.
 // . If a transient child and its transient parent share the same parent, then
 //   transient children are always ordered above the transient parent.
 // Transient windows are typically used for popups and menus.
-// TODO(sky): nuke this class and replace with calls to TransientWindowManager.
-// This is temporary until we start moving to ui/wm.
 class AURA_EXPORT TransientWindowClient {
  public:
   virtual void AddTransientChild(Window* parent, Window* child) = 0;
   virtual void RemoveTransientChild(Window* parent, Window* child) = 0;
   virtual Window* GetTransientParent(Window* window) = 0;
   virtual const Window* GetTransientParent(const Window* window) = 0;
+  virtual void AddObserver(TransientWindowClientObserver* observer) = 0;
+  virtual void RemoveObserver(TransientWindowClientObserver* observer) = 0;
 
  protected:
   virtual ~TransientWindowClient() {}
 };
 
 // Sets/gets the TransientWindowClient. This does *not* take ownership of
 // |client|. It is assumed the caller will invoke SetTransientWindowClient(NULL)
 // before deleting |client|.
 AURA_EXPORT void SetTransientWindowClient(TransientWindowClient* client);
 AURA_EXPORT TransientWindowClient* GetTransientWindowClient();
 
 }  // namespace client
 }  // namespace aura
 
-#endif  // UI_WM_PUBLIC_TRANSIENT_WINDOW_CLIENT_H_
+#endif  // UI_AURA_CLIENT_TRANSIENT_WINDOW_CLIENT_H_