Investigate using texture compression for wallpaper on ChromeOS. DXT1 or ETC1 should be available on most devices.

The wallpaper is static and we draw it a lot. The benefit would be reduced memory usage and improved performance from using less bandwidth when drawing wallpaper tiles.

We can even keep it compressed on disk to avoid compressing it at startup.

If we're concerned about quality then we can evaluate the quality of the built-in wallpapers and never compress custom wallpapers.