title: Use content script in custom chrome extension page
body: <p>In my chrome extension i have an extra page, that is open via</p>
  
  <pre><code>window.open(chrome.extension.getURL("manager.html")); 
  </code></pre>
  
  <p>On that page i would like to use some functions of my content script. But it seems the content script is not loaded at all on that page?</p>