Moves TransientWindowClient to ui/aura/client and adds observer

ui/aura/client/transient_window_client.h

Index: ui/aura/client/transient_window_client.h
diff --git a/ui/wm/public/transient_window_client.h b/ui/aura/client/transient_window_client.h
similarity index 81%
copy from ui/wm/public/transient_window_client.h
copy to ui/aura/client/transient_window_client.h
index 4ce537fec504d304c4825a838e7789490d340125..49088560b267e4f10427448c6bc04a1cd70a04c9 100644
--- a/ui/wm/public/transient_window_client.h
+++ b/ui/aura/client/transient_window_client.h
@@ -2,8 +2,8 @@
 // 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"
 
@@ -13,6 +13,8 @@ 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
@@ -21,14 +23,14 @@ namespace client {
 // . 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() {}
@@ -43,4 +45,4 @@ AURA_EXPORT TransientWindowClient* GetTransientWindowClient();
 }  // namespace client
 }  // namespace aura
 
-#endif  // UI_WM_PUBLIC_TRANSIENT_WINDOW_CLIENT_H_
+#endif  // UI_AURA_CLIENT_TRANSIENT_WINDOW_CLIENT_H_