[sessions] Properly namespace recently-componentized TabRestore code

components/sessions/core/tab_restore_service_observer.h

 // Copyright (c) 2010 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_SESSIONS_CORE_TAB_RESTORE_SERVICE_OBSERVER_H_
 #define COMPONENTS_SESSIONS_CORE_TAB_RESTORE_SERVICE_OBSERVER_H_
 
 #include "components/sessions/sessions_export.h"
 
+namespace sessions {
+
 class TabRestoreService;
 
 // Observer is notified when the set of entries managed by TabRestoreService
 // changes in some way.
 class SESSIONS_EXPORT TabRestoreServiceObserver {
  public:
   // Sent when the set of entries changes in some way.
   virtual void TabRestoreServiceChanged(TabRestoreService* service) = 0;
 
   // Sent to all remaining Observers when TabRestoreService's
   // destructor is run.
   virtual void TabRestoreServiceDestroyed(TabRestoreService* service) = 0;
 
   // Sent when TabRestoreService finishes loading.
   virtual void TabRestoreServiceLoaded(TabRestoreService* service) {}
 
  protected:
   virtual ~TabRestoreServiceObserver() {}
 };
 
+}  // namespace sessions
+
 #endif  // COMPONENTS_SESSIONS_CORE_TAB_RESTORE_SERVICE_OBSERVER_H_