Add device policy to disallow shutdown - ash UI modifications

ash/test/test_system_tray_delegate.cc

Index: ash/test/test_system_tray_delegate.cc
diff --git a/ash/test/test_system_tray_delegate.cc b/ash/test/test_system_tray_delegate.cc
index 60fb4b31e1fc4fc81fba6b930baad00985792c7b..19daea2b14f7ef2ffff29c51a4921ff635083c98 100644
--- a/ash/test/test_system_tray_delegate.cc
+++ b/ash/test/test_system_tray_delegate.cc
@@ -94,10 +94,6 @@ bool TestSystemTrayDelegate::GetSessionLengthLimit(
   return session_length_limit_set_;
 }
 
-void TestSystemTrayDelegate::ShutDown() {
-  base::MessageLoop::current()->Quit();
-}
-
 void TestSystemTrayDelegate::SignOut() {
   base::MessageLoop::current()->Quit();
 }