Add device_index parameter for camera performance test

BUG=None
TEST=Manually
Attach an external camera to a Chromebook, and pass device_index = 1

Change-Id: I3d71c8ad54c18c30a9d5f97a46727df4a13976c0
Reviewed-on: https://gerrit.chromium.org/gerrit/48636
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Commit-Queue: Justin Chuang <jchuang@chromium.org>
Tested-by: Justin Chuang <jchuang@chromium.org>
1 file changed