waiter = function(e) {
    // This is a packet from the wtf.ipc.MessageChannel type.
    var data = e.data;
    if (!data ||
        !data['wtf_ipc_connect_token'] ||
        !data['data']['hello']) {
      return;
    }

    // Stop snooping.
    e.preventDefault();
    e.stopPropagation();
    window.removeEventListener('message', waiter, true);

    if (opt_callback) {
      opt_callback.call(opt_scope, e.source);
    }
    e.source.focus();
  }
Shows the empty UI.
@param {Extension.ShowOptions?} options Options.
@private