Add device policy to disallow shutdown - ash UI modifications

ash/system/tray/default_system_tray_delegate.h

Index: ash/system/tray/default_system_tray_delegate.h
diff --git a/ash/system/tray/default_system_tray_delegate.h b/ash/system/tray/default_system_tray_delegate.h
index fede740d001a88eaf9cfbb84220c330b6657b750..041763f7ae9993626116de5dc965f7677b5b36ed 100644
--- a/ash/system/tray/default_system_tray_delegate.h
+++ b/ash/system/tray/default_system_tray_delegate.h
@@ -83,6 +83,10 @@ class ASH_EXPORT DefaultSystemTrayDelegate : public SystemTrayDelegate {
       CustodianInfoTrayObserver* observer) override;
   void RemoveCustodianInfoTrayObserver(
       CustodianInfoTrayObserver* observer) override;
+  void AddShutdownPolicyObserver(ShutdownPolicyObserver* observer) override;
+  void RemoveShutdownPolicyObserver(ShutdownPolicyObserver* observer) override;
+  void ShouldRebootOnShutdown(
+      const RebootOnShutdownCallback& callback) override;
 
  private:
   bool bluetooth_enabled_;