title: chrome.app.isInstalled always returns false for Google Chrome extensions?
body: <p>why does  chrome.app.isInstalled always return false for Google Chrome extensions? </p>
  
  <p>Dynamically I add a link element on page load:</p>
  
  <pre><code>&lt;link type="text/css" rel="chrome-webstore-item" href="https://chrome.google.com/webstore/detail/itemID"&gt;
  </code></pre>
  
  <p>The following is some Javascript that executes when a button has been clicked:</p>
  
  <pre><code>if (!chrome.app.isInstalled) {
   alert('extension is about to be installed!');
   install_extension();
  }else{
    alert('extension is installed already.');
  }
  </code></pre>
  
  <p>The first time I clicked the button, Google Chrome asked me if I wanted to install the extension. I agree and the extension was installed correctly. When I refreshed the page,  I clicked the button once again and Google CHrome asked me to install the extension once again even when I had installed it 2 minutes ago. <em>In other words, chrome.app.isInstalled always return false even when the extension is installed.</em> Why?</p>