background.html

<script>
  var statusURL = "http://travis-ci.org/builds/last.json";

  if (!localStorage.prefs) {
    // Default to notifications being on. 
    localStorage.prefs = JSON.stringify({ "use_notifications": true });
  }

  var lastOpen = null;
  var lastNotification = null;
  function notifyIfStatusChange(open, status) {
    var prefs = JSON.parse(localStorage.prefs);
    if (lastOpen && lastOpen != open && prefs.use_notifications) {
      if (lastNotification) {
        lastNotification.cancel();
      }
      var notification = webkitNotifications.createNotification(
          chrome.extension.getURL("icon.png"), "Tree is " + open, status);
      lastNotification = notification;
      notification.show();
    }
    lastOpen = open;
  }

  function updateStatus(status) {
    chrome.browserAction.setTitle({title:status});
    var open = /open/i;
    if (open.exec(status)) {
      notifyIfStatusChange("open", status);
      chrome.browserAction.setBadgeText({text:"\u2022"});
      chrome.browserAction.setBadgeBackgroundColor({color:[0,255,0,255]});
    } else {
      notifyIfStatusChange("closed", status);
      //chrome.browserAction.setBadgeText("\u2639");
      chrome.browserAction.setBadgeText({text:"\u00D7"});
      chrome.browserAction.setBadgeBackgroundColor({color:[255,0,0,255]});
    }
  }

  function requestStatus() {
    requestURL(statusURL, updateStatus);
    setTimeout(requestStatus, 30000);
  }

  function requestURL(url, callback) {
    //console.log("requestURL: " + url);
    var xhr = new XMLHttpRequest();
    try {
      xhr.onreadystatechange = function(state) {
        if (xhr.readyState == 4) {
          var text = xhr.responseText;
          //console.log(text);
          callback(text);
        }
      }

      xhr.onerror = function(error) {
        console.log("xhr error: " + JSON.stringify(error));
        console.dir(error);
      }

      xhr.open("GET", url, true);
      xhr.send({});
    } catch(e) {
      console.log("exception: " + e);
    }
  }

  window.onload = function() {
    window.setTimeout(requestStatus, 10);
  }
</script>