title: TypeError: Attempting to change configurable attribute of unconfigurable property of iframe's src
body: <p>When below code is executed in chrome, firefox, no error comes. But safari throws TypeError: Attempting to change configurable attribute of unconfigurable property. 
  I don't understand if src is inconfigurable then why don't error comes for chrome and firefox. </p>
  
  <pre><code>Object.defineProperty(iframe, 'src', {
      writable: false, configurable: true
  });
  </code></pre>
  
  <p>Safari Version 11.0.1<br>
  PS - I know changing the existing non-configurable property throws this error but then why not chrome and firefox</p>