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 7a7a4ff20d371a544fad795a0b840d770eeb5399..041763f7ae9993626116de5dc965f7677b5b36ed 100644
--- a/ash/system/tray/default_system_tray_delegate.h
+++ b/ash/system/tray/default_system_tray_delegate.h
@@ -49,7 +49,6 @@ class ASH_EXPORT DefaultSystemTrayDelegate : public SystemTrayDelegate {
   void ShowEnterpriseInfo() override;
   void ShowSupervisedUserInfo() override;
   void ShowUserLogin() override;
-  void ShutDown() override;
   void SignOut() override;
   void RequestLockScreen() override;
   void RequestRestartForUpdate() override;
@@ -84,6 +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_;