Rework FocusManager as FocusClient.

ui/aura/client/focus_change_observer.h

Index: ui/aura/client/focus_change_observer.h
===================================================================
--- ui/aura/client/focus_change_observer.h	(revision 169818)
+++ ui/aura/client/focus_change_observer.h	(working copy)
@@ -2,15 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef UI_AURA_FOCUS_CHANGE_OBSERVER_H_
-#define UI_AURA_FOCUS_CHANGE_OBSERVER_H_
+#ifndef UI_AURA_CLIENT_FOCUS_CHANGE_OBSERVER_H_
+#define UI_AURA_CLIENT_FOCUS_CHANGE_OBSERVER_H_
 
 #include "ui/aura/aura_export.h"
 
 namespace aura {
-
 class Window;
+namespace client {
 
+// TODO(beng): this interface will be OBSOLETE by FocusChangeEvent.
 class AURA_EXPORT FocusChangeObserver {
  public:
   // Called when |window| gains focus.
@@ -20,6 +21,7 @@
   virtual ~FocusChangeObserver() {}
 };
 
+}  // namespace client
 }  // namespace aura
 
-#endif  // UI_AURA_FOCUS_CHANGE_OBSERVER_H_
+#endif  // UI_AURA_CLIENT_FOCUS_CHANGE_OBSERVER_H_