plugins/npapi/prebuilt/gwt-dev-plugin/page_action.html

<head>
  <style>
    body {
      width: 20em;
    }
  </style>
  <script>
    function getParam(key) {
      var idx = window.location.search.indexOf(key + "=");
      var value = '';
      if (idx >= 0) {
        idx += key.length + 1;
        value = window.location.search.substring(idx).split('&')[0];
      }
      return value;
    }

    function init() {
      var permission = getParam('permission');
      var host = getParam('host');
      var message='';

      if (permission == 'include') {
        message = 'The host at ' + host + ' is allowed to use the plugin';
      } else if (permission == 'exclude') {
        message = 'The host at ' + host + ' has been been blacklisted.';
      } else if (permission == 'unknown') {
        message = 'The host at ' + host + ' is unknown to the plugin.';
      }

      document.getElementById('message').innerText = message;
    }

    function updateConfiguration() {
      var url = 'DevModeOptions.html?host=' + getParam('host');
      url = chrome.extension.getURL(url);
      chrome.tabs.create({'url' : url});
    }
  </script>
</head>
<body onload='javascript:init()'>
  <h3>GWT Developer Plugin</h3>
  <div id='message'></div>
  <br/>
  <button onclick= "updateConfiguration()">Update Your Configuration</button>
  </p>
</body>