code: function createTabPanel(path, name, options, callback) {
      tabbar.addPanel(new wtf.app.AddonTabPanel(
          addon, documentView, path, name, options, callback));
    }
docs: Creates a new tab panel.
  Part of the app addon API.
  @param {string} path Path used for navigation.
  @param {string} name Panel name.
  @param {Object} options Options.
  @param {wtf.app.AddonTabPanel.Callback} callback
  A callback that creates an external panel.