chromium: Link against pulse instead of dlopen().

This fixes the issue of Chromium not being able to load the pulseaudio
librarp

We could also propagate the build inputs, but it would end up being the
same as just directoly linking against the library.

Thanks to @aristidb for noticing this in #2421:

https://github.com/NixOS/nixpkgs/pull/2421#issuecomment-42113656



Signed-off-by: aszlig <aszlig@redmoonstudios.org>