title: Check DOM element in Google Chrome Extension
body: <p>I am trying to make a simple Google Chrome extension - like finding a specific element on the page and display an alert.</p>
  
  <p>My problem is that the specific page loads relatively slow (having also some AJAX behind). </p>
  
  <p>How can I make my check only when all the page is loaded?</p>
  
  <p>I tried <code>"run_at" : "document_idle"</code> in my manifest file, but with no success. It shows me the message, before the whole page loads.</p>
  
  <p>I was thinking to check every second (or something) the whole DOM elements, but is this a feasible solution? I think it will slow down the page...</p>
  
  <p>Thanks.</p>