title: flutter_webview_plugin how to listen on url changed for javascript
body: <p>I'm using flutter_webview_plugin
  I need to listen on url changed. 
  I found when the url changed for javascript, the method 'onUrlChanged.listen' is not working.
  Could anybody help me to solve this problem?</p>
  
  <p><a href="https://i.stack.imgur.com/PGXx0.png" rel="nofollow noreferrer">Here's my code</a></p>