video_MultiplePlayback is flaky.
It randomly failed on many boards with following exception

  File "/usr/local/autotest/tests/video_MultiplePlayback/video_MultiplePlayback.py", line 91, in run_once
    self.run_video_tests(cr.browser)
  File "/usr/local/autotest/tests/video_MultiplePlayback/video_MultiplePlayback.py", line 62, in run_video_tests
    timeout=5)

ReferenceError: testvideo is not defined