Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.
This is a convenience helper to instantiate a GIcon like so:
auto icon = GIcon::default_icon("filetype-image");
This will give you the "filetype-image" icon in both 16x16 and 32x32 sizes.
