cros: Clean up SessionStateDelegate refs in Chrome

components/user_manager/user_manager.h

Index: components/user_manager/user_manager.h
diff --git a/components/user_manager/user_manager.h b/components/user_manager/user_manager.h
index fbf4cc185bf66865199b23ff1c50a531d5b03759..1029959282f0755e1e043a784c87ac2a2172d9d0 100644
--- a/components/user_manager/user_manager.h
+++ b/components/user_manager/user_manager.h
@@ -55,7 +55,7 @@ class USER_MANAGER_EXPORT UserManager {
     virtual ~Observer();
   };
 
-  // TODO(nkostylev): Refactor and move this observer out of UserManager.
+  // TODO(xiyuan): Refactor and move this observer out of UserManager.
   // Observer interface that defines methods used to notify on user session /
   // active user state changes. Default implementation is empty.
   class UserSessionStateObserver {
@@ -395,6 +395,19 @@ class USER_MANAGER_EXPORT UserManager {
   static UserManager* SetForTesting(UserManager* user_manager);
 };
 
+// TODO(xiyuan): Move this along with UserSessionStateObserver
+class USER_MANAGER_EXPORT ScopedUserSessionStateObserver {
+ public:
+  explicit ScopedUserSessionStateObserver(
+      UserManager::UserSessionStateObserver* observer);
+  ~ScopedUserSessionStateObserver();
+
+ private:
+  UserManager::UserSessionStateObserver* const observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedUserSessionStateObserver);
+};
+
 }  // namespace user_manager
 
 #endif  // COMPONENTS_USER_MANAGER_USER_MANAGER_H_