chromium: Prefer local build on source derivation.

It doesn't make sense to do the splitting of the source code on a remote
machine, so don't try to do it.

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

pkgs/applications/networking/browsers/chromium/source/default.nix

@@ -69,6 +69,8 @@ stdenv.mkDerivation {
     rm -rf "$out/tools/gyp" # XXX: Don't even copy it in the first place.
   '';
 
+  preferLocalBuild = true;
+
   passthru = {
     inherit version channel;
     plugins = fetchurl binary;