This update is a bit more problematic, as the bundled version of libpng is
version 1.2.45 and the version in nixpkgs is 1.5.13. Even if trying to run with
libpng12 from nixpkgs, it seems to collide with parts of the bundled version.
So, until this is either fixed upstream or we have a good solution, we're using
bundled libpng for chromium version 25 and higher.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>