title: iframe inside WKWebView issues
body: <p>I have WKWebView where I load html content with loadHTMLString method. In my html code I have two iframes:</p>
  
  <pre><code>&lt;iframe align=\"middle\"
   allowtransparency=\"\"
   frameborder=\"0\"
   height=\"820px\"
   id=\"\"
   scrolling=\"no\"
   seamless=\"\"
   src=\"//my.site.ru/files_static/edd/2016/speech_countries/6/first.html\" 
   width=\"100%\"&gt;
  &lt;/iframe&gt;
  &lt;iframe align=\"middle\"
   allowtransparency=\"\"
   frameborder=\"0\"
   height=\"820px\"
   id=\"\"
   scrolling=\"no\"
   seamless=\"\"
   src=\"http://my.sample.ru/files_static/edd/2016/speech_countries/6/first.html\" 
   width=\"100%\"&gt;
  &lt;/iframe&gt;
  </code></pre>
  
  <p>Then I call loadHTMLString(myHtmlString, baseURL: URL(string: "<a href="https://example.ru" rel="nofollow noreferrer">https://example.ru</a>")) and have following situation: 
  1) first iframe loaded successfully
  2) second iframe is empty</p>
  
  <p>If I use <a href="http://example.ru" rel="nofollow noreferrer">http://example.ru</a> as a base url then both iframes loads successfully. But I still can't get why I can't use https protocol in my base url</p>