title: Get an unsigned int milliseconds out of chrono::duration
body: <p>For a winapi wrapper I want to use chrono for a duration given to the call. The code example:</p>
  
  <pre><code>bool setTimer(std::chrono::duration&lt;std::chrono::milliseconds&gt; duration)
  {
      unsigned int dwDuration = Do some chrono magic here
  
      SetTimer(m_hWnd,1,dwDuration,0);
  }
  </code></pre>
  
  <p>dwDuration has to be in milliseconds.</p>
  
  <p>First question: How do to the magic.</p>
  
  <p>Second question: Is the parameter declaration okay?</p>