Add device policy to disallow shutdown - ash UI modifications

ash/system/tray/default_system_tray_delegate.cc

Index: ash/system/tray/default_system_tray_delegate.cc
diff --git a/ash/system/tray/default_system_tray_delegate.cc b/ash/system/tray/default_system_tray_delegate.cc
index 66f5d12e7e85fadc7d874de5ac1a7995a9b828ea..1c1147f4622b12f592729052cad58a8e79c1542b 100644
--- a/ash/system/tray/default_system_tray_delegate.cc
+++ b/ash/system/tray/default_system_tray_delegate.cc
@@ -269,4 +269,16 @@ void DefaultSystemTrayDelegate::RemoveCustodianInfoTrayObserver(
     CustodianInfoTrayObserver* observer) {
 }
 
+void DefaultSystemTrayDelegate::AddShutdownPolicyObserver(
+    ShutdownPolicyObserver* observer) {
+}
+
+void DefaultSystemTrayDelegate::RemoveShutdownPolicyObserver(
+    ShutdownPolicyObserver* observer) {
+}
+
+void DefaultSystemTrayDelegate::ShouldRebootOnShutdown(
+    const RebootOnShutdownCallback& callback) {
+}
+
 }  // namespace ash