gistfile1.php

$button_slug = 'fetch';

$js_button_data = array(
          'qt_button_text'    => __( 'iframe' ),
          'button_tooltip'    => __( 'iframe' ),
          'icon'              => 'dashicons-admin-appearance',
          'l10ncancel'        => __( 'Cancel' ),
          'l10ninsert'        => __( 'Insert' ),
          'modalHeight'       => '400',
          //'width'             => 500,
);

$additional_args = array(
          'cmb_metabox_config'   => 'shortcode_button_cmb_config',
);

$button = new _Shortcode_Button_( $button_slug, $js_button_data, $additional_args );


function shortcode_button_cmb_config( $button_data ) {
    return array(
        'id'     => 'myplugin_shortcode_'. $button_data['slug'],
        'fields' => array(
            array(
                'name'              => __( 'URL/link' ),
                'id'                => 'url',
				'type'              => 'text_url',
				'protocols'         => array( 'http', 'https' ),
                              ),
			array(
				'name'              => __( 'Scrolling' ),
				'id'                => 'scrolling',
				'type'              => 'select',
				'options'           => array( 'no' => __( 'No' ), 'yes' => __( 'Yes' ), ),
			),
        ),
        'show_on' => array( 'key' => 'options-page', 'value' => $button_data['slug'] ),
    );
}

function iframe_shortcode( $atts ) {
          extract( shortcode_atts( array(
                    'url'           => '',
                    'scrolling'     => 'no',
                    'width'         => '100%',
                    'height'        => '500px',
                    'class'         => '',    
          ), $atts ) );

	if ( empty( $url ) ) {
		return false;	
	} else {
		return '<iframe class="' . $class . '" src="' . $url . '" width="' . $width . '" height="' . $height . '" scrolling="' . $scrolling . '" frameborder="0" marginheight="0"></iframe>';
	}
}
add_shortcode( 'fetch', 'iframe_shortcode' );