Provide a form for setting options.
Overrides RowPluginBase::buildOptionsForm
public function buildOptionsForm(&$form, &$form_state) {
parent::buildOptionsForm($form, $form_state);
$form['item_length'] = array(
'#type' => 'select',
'#title' => t('Display type'),
'#options' => $this
->options_form_summary_options(),
'#default_value' => $this->options['item_length'],
);
$form['links'] = array(
'#type' => 'checkbox',
'#title' => t('Display links'),
'#default_value' => $this->options['links'],
);
}