Convert "duration" "Unit" to milliseconds
<p>I want to have an API that looks like</p>

<pre><code>public static long toMillis ( long duration, ChronoUnit unit ) {
   // magic duration to millis
}

toMillis( 5, ChronoUnit.SECONDS); // 5000
</code></pre>

<p>of course I'm not actually writing <code>toMillis</code> but that's essentially what I'm trying to do.</p>