video_playback: Enable Cras output

Enable Cras output so the test can play audio.

BUG=chrome-os-partner:39490
TEST=run video_playback test with chrome UI setting mute.

Change-Id: I3e0cc0430bfd6b4a8648e546ad334f830b63b4fa
Reviewed-on: https://chromium-review.googlesource.com/293974
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
1 file changed