title: How to prevent WKWebView from being emptied after app sent to background
body: <p>I am developing an app that uses <code>WKWebView</code> to render web content.
  Everything works fine so far except one thing: if I load a page on my <code>WKWebView</code> then send the app to the background for a while (I'd say around ten minutes) and reopen the app, my <code>WKWebView</code> is empty.</p>
  
  <p>I guess it is automatically emptied to prevent memory waste, but then what do Safari or Chrome do in order to keep the web page content in memory?</p>