Makes SetFocus() notify callback correctly on failure

components/mus/ws/window_server.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 COMPONENTS_MUS_WS_WINDOW_SERVER_H_
 #define COMPONENTS_MUS_WS_WINDOW_SERVER_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 116 matching lines @@
         const_cast<const WindowServer*>(this)->GetTreeWithRoot(window));
   }
   const WindowTree* GetTreeWithRoot(const ServerWindow* window) const;
 
   void OnFirstWindowManagerFactorySet();
 
   WindowManagerFactoryRegistry* window_manager_factory_registry() {
     return &window_manager_factory_registry_;
   }
 
-  void SetFocusedWindow(ServerWindow* window);
+  // Sets focus to |window|. Returns true if |window| already has focus, or
+  // focus was successfully changed. Returns |false| if |window| is not a valid
+  // window to receive focus.
+  bool SetFocusedWindow(ServerWindow* window);
   ServerWindow* GetFocusedWindow();
 
   // Returns a change id for the window manager that is associated with
   // |source| and |client_change_id|. When the window manager replies
   // WindowManagerChangeCompleted() is called to obtain the original source
   // and client supplied change_id that initiated the called.
   uint32_t GenerateWindowManagerChangeId(WindowTree* source,
                                          uint32_t client_change_id);
 
   // Called when a response from the window manager is obtained. Calls to
@@ skipping 146 matching lines @@
 
   WindowManagerFactoryRegistry window_manager_factory_registry_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowServer);
 };
 
 }  // namespace ws
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_WS_WINDOW_SERVER_H_