process_tags() public method

Doesn't create a tag if its slug already exists
public process_tags ( )
 public function wpImportContents($file)
 {
     $wp_import = new WP_Import();
     $wp_import->fetch_attachments = false;
     // doesn matter
     // load data from saved option
     $wp_import->post_orphans = get_option('_cri_post_orphans', array());
     $wp_import->processed_posts = get_option('_cri_processed_posts', array());
     $wp_import->url_remap = get_option('_cri_url_remap', array());
     // the odd filter
     add_filter('import_post_meta_key', array($wp_import, 'is_valid_meta_key'));
     add_filter('http_request_timeout', array(&$wp_import, 'bump_request_timeout'));
     // start buffer
     ob_start();
     // parse file and gather data
     $wp_import->import_start($file);
     // map author
     $wp_import->get_author_mapping();
     wp_suspend_cache_invalidation(true);
     $wp_import->process_categories();
     $wp_import->process_tags();
     $wp_import->process_terms();
     $wp_import->process_posts();
     wp_suspend_cache_invalidation(false);
     // update incorrect/missing information in the DB
     $wp_import->backfill_parents();
     $wp_import->backfill_attachment_urls();
     $wp_import->remap_featured_images();
     // end has output, so buffer it out
     $wp_import->import_end();
     // ignore the output, call in buffer
     do_action('radium_after_content_import');
     ob_end_clean();
     // delete all attachment related stats
     foreach (array('_cri_post_orphans', '_cri_processed_posts', '_cri_url_remap') as $op) {
         delete_option($op);
     }
     return true;
 }