title: About debugging chrome extension
body: <p>I am learning chrome extension by example. Here is the example I currently learning: <a href="http://www.chrome-extensions.net/extensions/mappy/" rel="noreferrer">http://www.chrome-extensions.net/extensions/mappy/</a></p>
  
  <p>There are three JavaScript files in this sample project: background.js mappy_content_script.js popup.js. </p>
  
  <p>"mappy_content_script.js" is shown in the Combo box of Scripts tab of Developer Tools.<br>
  "popup.js" can be found if I right click the extension icon and choose "Inspect popup".</p>
  
  <p>The problem is I can't debug "background.js" or find it in the Developer Tools. I tried insert "debugger;" in this JavaScript file. I also tried use profiling tool to record the script execution. However, when I click the link of "background.js", a blank page shows up.
  <img src="https://i.stack.imgur.com/r0EFD.png" alt="Profile Tool"></p>
  
  <p>Is this a bug of chrome or did I miss something? Thanks</p>