[sessions] Properly namespace recently-componentized TabRestore code

components/sessions/core/tab_restore_service_observer.h

Index: components/sessions/core/tab_restore_service_observer.h
diff --git a/components/sessions/core/tab_restore_service_observer.h b/components/sessions/core/tab_restore_service_observer.h
index 94f05df083b89e72e66bc64ccdf25bee32dc00e4..1a785ad4f93252d17d84b1e4b2346df97822f4d6 100644
--- a/components/sessions/core/tab_restore_service_observer.h
+++ b/components/sessions/core/tab_restore_service_observer.h
@@ -7,6 +7,8 @@
 
 #include "components/sessions/sessions_export.h"
 
+namespace sessions {
+
 class TabRestoreService;
 
 // Observer is notified when the set of entries managed by TabRestoreService
@@ -27,4 +29,6 @@ class SESSIONS_EXPORT TabRestoreServiceObserver {
   virtual ~TabRestoreServiceObserver() {}
 };
 
+}  // namespace sessions
+
 #endif  // COMPONENTS_SESSIONS_CORE_TAB_RESTORE_SERVICE_OBSERVER_H_