Add SessionStateObserver with ActiveUserChanged()

ash/session_state_delegate_stub.cc

 // Copyright (c) 2013 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.
 
 #include "ash/session_state_delegate_stub.h"
 
 #include "ash/shell.h"
 #include "ash/shell/example_factory.h"
 #include "base/string16.h"
 #include "base/utf_string_conversions.h"
@@ skipping 52 matching lines @@
   return null_image_;
 }
 
 void SessionStateDelegateStub::GetLoggedInUsers(
     UserEmailList* users) {
 }
 
 void SessionStateDelegateStub::SwitchActiveUser(const std::string& email) {
 }
 
+void SessionStateDelegateStub::AddSessionStateObserver(
+    ash::SessionStateObserver* observer) {
+}
+
+void SessionStateDelegateStub::RemoveSessionStateObserver(
+    ash::SessionStateObserver* observer) {
+}
+
 }  // namespace ash