Gravatar Prefetch Example

gravatar-prefetch.php

<?php

/* 
 * Adding DNS Prefetching
 */
    function dns_prefetch() {
        echo '<meta http-equiv="x-dns-prefetch-control" content="on">
        <link rel="dns-prefetch" href="//fonts.googleapis.com" />
        <link rel="dns-prefetch" href="//fonts.gstatic.com" />
        <link rel="dns-prefetch" href="//0.gravatar.com/" />
        <link rel="dns-prefetch" href="//2.gravatar.com/" />
        <link rel="dns-prefetch" href="//1.gravatar.com/" />';
    }
    add_action('wp_head', 'dns_prefetch', 0);