Add missing status div (GoogleChrome#476)

Author: beaufortfrancois

service-worker/prefetch-video/index.html

@@ -5,6 +5,8 @@
 local_js_files: ['index.js', 'service-worker.js']
 ---
 
+<div id="status"></div>
+
 <video controls  poster="static/poster.jpg"
   style="margin: 0 0 1em 0; max-width: 100%; width: 480px;">
   <!-- Videos are stored remotely with CORS enabled -->