woocommerce/classes/walkers/class-product-cat-dropdown-walker.php

<?php
/**
 * WC_Product_Cat_Dropdown_Walker class.
 * 
 * @extends Walker
 */
class WC_Product_Cat_Dropdown_Walker extends Walker {

	var $tree_type = 'category';
	var $db_fields = array ('parent' => 'parent', 'id' => 'term_id', 'slug' => 'slug' );

	/**
	 * @see Walker::start_el()
	 * @since 2.1.0
	 *
	 * @param string $output Passed by reference. Used to append additional content.
	 * @param object $category Category data object.
	 * @param int $depth Depth of category in reference to parents.
	 * @param array $args
	 */
	function start_el(&$output, $cat, $depth, $args) {
		$pad = str_repeat('&nbsp;', $depth * 3);

		$cat_name = apply_filters( 'list_product_cats', $cat->name, $cat );
		$output .= "\t<option class=\"level-$depth\" value=\"" . $cat->slug . "\"";
		
		if ( $cat->slug == $args['selected'] )
			$output .= ' selected="selected"';
			
		$output .= '>';
		
		$output .= $pad . __( $cat_name, 'woocommerce' );
		
		if ( $args['show_count'] )
			$output .= '&nbsp;(' . $cat->count . ')';
			
		$output .= "</option>\n";
	}
}