title: Sending message between content.js and background.js fails
body: <p>I am trying to send a url from <code>content.js</code> to <code>background.js</code> to make an <code>ajax</code> request there.</p>
  <p>In <code>content.js</code> I have the following code. By the way, this message sending from content.js to background.js works and I have tested it. But the problem is that I am getting no response from background.js back. I have also tested that <code>ajax</code> request was made successfully.</p>
  <pre class="lang-js prettyprint-override"><code>$(document).on('click', '.readmore a', function(event) {
      event.preventDefault();
      var link = $(this).attr('href');
  
      chrome.runtime.sendMessage(extractFacebookUrl(link), function(response){
          console.log(response); //nothing get consoled out here.
      });
  });
  </code></pre>
  <p>In <code>background.js</code>, I have the following code.</p>
  <pre class="lang-js prettyprint-override"><code>chrome.runtime.onMessage.addListener(function(url, sender, response){
      $.get(url, function(data){
          obj = {'data' : data, 'link' : url}
          //alert(data); //This alert shows that ajax request was successful.
          response(obj); //But this returns nothing to content.js. Why?
      });
  });
  </code></pre>