Returns example content for dialog tests.
function ajax_test_dialog_contents() {
  // This is a regular render array; the keys do not have special meaning.
  $content = array(
    'content' => array(
      '#markup' => 'Example message',
    ),
    'cancel' => array(
      '#type' => 'link',
      '#title' => 'Cancel',
      '#href' => '',
      '#attributes' => array(
        // This is a special class to which JavaScript assigns dialog closing
        // behavior.
        'class' => array(
          'dialog-cancel',
        ),
      ),
    ),
  );
  return $content;
}