title: How to make Chrome extension workable even page says ERR_CONNECTION_RES
body: <p>I want to develop a google chrome extension which replaces url to another if page is not available.I mean it responses 
  *The server DNS address of the example.com host machine could not be found.
  *ERR_CONNECTON_RES</p>
  
  <p>or same as these stuations.</p>
  
  <p>I have searched how extensions work and found these extentions run after DOM is completed.But i believe that there is no impossible thing.</p>
  
  <p>Is there a any code i can add to run the extension before DOM is completed to content.js.</p>