title: How to use getUserMedia from TypeScript
body: <p>I'd like to call  <a href="http://www.html5rocks.com/en/tutorials/getusermedia/intro/" rel="noreferrer">getUserMedia</a> from TypeScript, something like: </p>
  
  <pre><code> return  navigator.getUserMedia()
  </code></pre>
  
  <p>However, TypeScript's definition of Navigator (in lib.d.ts)  doesn't contain getUserMedia. 
  How do I work around? Should I be modifying lib.d.ts?  Where do I make this change?</p>