title: Convert "duration" "Unit" to milliseconds
body: <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>