This repo for WhaleOS is based on https://chromium.googlesource.com/chromiumos/platform/chromiumos-assets/.
This repository chromiumos-assets contains the unofficial, Chromium OS versions of assets (images, sounds, etc.) that differ between official and unofficial builds. These files are installed by the chromiumos-assets package.
See also the chromeos-assets (internal only) repo which has official resources, and the assets repo which has resources shared between the two builds.