Add device policy to disallow shutdown - ash UI modifications

ash/system/chromeos/shutdown_policy_observer.h

Index: ash/system/chromeos/shutdown_policy_observer.h
diff --git a/ash/system/chromeos/shutdown_policy_observer.h b/ash/system/chromeos/shutdown_policy_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..92a8e8121d6440afd0b31fe7f9e8b2c2d5f5cbc9
--- /dev/null
+++ b/ash/system/chromeos/shutdown_policy_observer.h
@@ -0,0 +1,22 @@
+// Copyright 2014 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.
+
+#ifndef ASH_SYSTEM_CHROMEOS_SHUTDOWN_POLICY_OBSERVER_H_
+#define ASH_SYSTEM_CHROMEOS_SHUTDOWN_POLICY_OBSERVER_H_
+
+namespace ash {
+
+// Registered with SystemTrayDelegate to observe the |kRebootOnShutdown| policy.
+class ASH_EXPORT ShutdownPolicyObserver {
+ public:
+  // Called when the value of the |kRebootOnShutdown| policy is changed.
+  virtual void OnShutdownPolicyChanged(bool reboot_on_shutdown) = 0;
+
+ protected:
+  virtual ~ShutdownPolicyObserver() {}
+};
+
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_CHROMEOS_SHUTDOWN_POLICY_OBSERVER_H_