title: UWP on desktop closed by top X button - no event
body: <p>An UWP app which runs on desktop can be closed from the top X button but it doesn't have any event for it. It is known that on phones and tablets an app should rely on <code>Suspending</code> event, no matter how it's triggered and then the app should rely on <a href="https://msdn.microsoft.com/EN-US/library/windows/apps/windows.applicationmodel.activation.applicationexecutionstate.aspx" rel="noreferrer"><code>ApplicationExecutionState</code></a>.</p>
  
  <p>However, here is a (maybe) common scenario: on phones the <code>Suspending</code> event suffice and in case a Voip call is going on it will be operated by OS after the app is suspended. <strong>On desktop the close button is expected, by user, to completely close the app.</strong> So if a call is on going it should be hanged up and certain resources should be released.</p>
  
  <p>How can I know when the user clicked the "close" button if (and only if) the UWP app is running on desktop? </p>