Skip syncing if image_dir does not exist Devserver should assume no image exists if image_dir is not found. BUG=chromium:337533 TEST=None Change-Id: I1fc03a53491711d5d3db6107a1aeaf5102b73b00 Reviewed-on: https://chromium-review.googlesource.com/183543 Reviewed-by: Yu-Ju Hong <yjhong@chromium.org> Tested-by: Yu-Ju Hong <yjhong@chromium.org> Commit-Queue: Yu-Ju Hong <yjhong@chromium.org>