title: Chrome extension warns "Cannot load extension with file or directory name Thumbs.db. The filename is illegal."
body: <p>Whenever I use "<em>load unpacked</em>" to test my custom Chrome extension, I get an error:</p>
  
  <blockquote>
    <p>There were warnings when trying to install this extension:</p>
    
    <ul>
    <li>Cannot load extension with file or directory name Thumbs.db. The filename is illegal.</li>
    </ul>
  </blockquote>
  
  <p>I am testing my extension by:</p>
  
  <ul>
  <li>Opening Chrome's extensions page (<code>chrome://extensions</code>)</li>
  <li>Ensuring "<em>Developer mode</em>" is enabled in the top-right corner</li>
  <li>Clicking "<em>Load unpacked</em>" and selecting my extension folder.</li>
  </ul>
  
  <p>I don't see <code>Thumbs.db</code> in my extension folder, so I'm not sure what the warning is for.</p>