[This call is failing on TravisCI](https://travis-ci.org/mozilla-b2g/gaia/jobs/12292168). If you can't reproduce locally, it may be due to a race condition. The TravisCI machines are somewhat low-powered, so they tend to challenge assumptions we make about the behavior of the applications. Let me know if you're able to isolate the cause of this failure

Error log:

```
  1) using the video menu "before each" hook:
     Uncaught 
  NoSuchElement: (7) Unable to locate element: ul.thumbnail-group-container li
  Remote Stack:
  <none>
      at Error.MarionetteError (/home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/error.js:67:13)
      at Object.Client._handleCallback (/home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/client.js:463:19)
      at /home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/client.js:492:21
      at TcpSync.send (/home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/drivers/tcp-sync.js:94:10)
      at Object.send (/home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/client.js:444:36)
      at Object.Client._sendCommand (/home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/client.js:485:19)
      at Object._findElement (/home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/client.js:1257:19)
      at Object.findElement (/home/travis/build/mozilla-b2g/gaia/node_modules/marionette-client/lib/marionette/client.js:1303:32)
      at Object.thumbnail (/home/travis/build/mozilla-b2g/gaia/apps/video/test/marionette/video.js:39:24)
      at ReadStream.<anonymous> (/home/travis/build/mozilla-b2g/gaia/apps/video/test/marionette/video_info_test.js:24:39)
      at ReadStream.g (events.js:175:14)
      at ReadStream.EventEmitter.emit (events.js:117:20)
      at _stream_readable.js:910:16
      at process._tickCallback (node.js:415:13)
```