title: SpeechSynthesis API onend callback not working
body: <p>I'm using the <a href="https://dvcs.w3.org/hg/speech-api/raw-file/tip/speechapi.html#tts-section" rel="noreferrer">Speech Synthesis API</a> on Google Chrome v34.0.1847.131. The API is implemented in Chrome starting in v33.</p>
  
  <p>The text-to-speech works for the most part, except when assigning a callback to <code>onend</code>. For instance, the following code:</p>
  
  <pre><code>var message = window.SpeechSynthesisUtterance("Hello world!");
  message.onend = function(event) {
      console.log('Finished in ' + event.elapsedTime + ' seconds.');
  };
  window.speechSynthesis.speak(message);
  </code></pre>
  
  <p>will sometimes call <code>onend</code> and sometimes not call it. The timing appears to be completely off. When it does get called, the printed <code>elapsedTime</code> is always some epoch time like <code>1399237888</code>.</p>