Example usage:
var windowWatcher = Components.classes["@mozilla.org/embedcomp/window-watcher;1"].
getService(Components.interfaces.nsIWindowWatcher);
var progress = new Scholar.ProgressWindow(windowWatcher.activeWindow);
progress.changeHeadline('Indexing item...');
progress.addLines(['All About Foo'], ['chrome://scholar/skin/treeitem-book.png']);
progress.addDescription('Bar bar bar bar bar');
progress.show();
progress.fade();
