Debug RSS Widgets Cache

<?php
/*
Plugin Name: Debug RSS Widgets Cache
Version: 0.1
Plugin URI: http://ru.forums.wordpress.org/topic/21580
Description: Allows to see when the RSS widgets cache expires.
Author: Sergey Biryukov
Author URI: http://profiles.wordpress.org/sergeybiryukov/
*/

function drwc_dashboard_widget() {
    require_once( ABSPATH . WPINC . '/class-feed.php' );

    $rss_widget = new WP_Widget_RSS();
    $instances = $rss_widget->get_settings();
?>
<p>Current time: <?php echo date_i18n( 'd.m.Y H:i:s' ); ?></p>
<?php if ( ! empty( $instances ) ) : ?>
<table id="rss-cache" cellspacing="0">
<tr>
    <th>URL</th>
    <th>Cache Status</th>
</tr>
<?php
    foreach ( (array) $instances as $instance ) :
        $feed = new SimplePie();
        $feed->set_feed_url( $instance['url'] );
        $feed->set_cache_class( 'WP_Feed_Cache' );
        $feed->set_file_class( 'WP_SimplePie_File' );
        $feed->set_cache_duration( apply_filters( 'wp_feed_cache_transient_lifetime', 43200, $instance['url'] ) );
        do_action_ref_array( 'wp_feed_options', array( &$feed, $instance['url'] ) );

        $cache_status = 'Unknown';
        if ( ! $feed->cache ) {
            $cache_status = 'Disabled';
        } else {
            $cache = call_user_func( array( $feed->cache_class, 'create' ), $feed->cache_location, call_user_func( $feed->cache_name_function, $feed->feed_url ), 'spc' );
            if ( $cache ) {
                if ( $cache->mtime() )
                    $cache_status = 'Expires: ' . date_i18n( 'd.m.Y H:i', $cache->mtime() + $feed->cache_duration + get_option( 'gmt_offset' ) * 3600 );
                else
                    $cache_status = 'Expired';
            } else {
                $cache_status = 'Could not create WP_Feed_Cache object.';
            }
        }
?>
<tr>
    <td><a href="<?php echo esc_url( $instance['url'] ); ?>"><?php echo $instance['url']; ?></a></td>
    <td><?php echo $cache_status; ?></td>
</tr>
<?php
    endforeach;
?>
</table>
<?php else : ?>
<p>No RSS widgets found.</p>
<?php endif; ?>
<?php
}

function drwc_dashboard_widget_style() { ?>
<style type="text/css">
#rss-cache {
    width: 100%;
}
#rss-cache th {
    font-size: 12px;
    text-align: left;
    padding-bottom: 12px;
}
</style>
<?php
}
add_action( 'admin_head-index.php', 'drwc_dashboard_widget_style' );

function drwc_add_dashboard_widget() {
    wp_add_dashboard_widget( 'rss_cache', 'RSS Widgets Cache', 'drwc_dashboard_widget' );
}
add_action( 'wp_dashboard_setup', 'drwc_add_dashboard_widget' );
?>