function add_share_button($atts, $content = null )
    {
            $atts = shortcode_atts(
                    array(
                        'url' => 'https://www.google.com.hk/',
                        'layout' => 'button'
                    ), $atts
             );

            return  '<div class = "fb-share-button" data-href="'.$atts['url'].'" data-layout="button"></div>';
    }

  add_shortcode('test_lmc', 'add_share_button');