Re-re-revert "chromium: remove preferLocalBuild".

This reverts commit 0696b0ef.

Okay, now finally, let's get this straight. We actually *want*
preferLocalBuild, *because* we have improved the source splitup in
c92dbffe

.

The idea is to use local builds in order to prevent the source being
pushed to a remote machine, splitted up there (and thus copied again)
and then being copied *again* FROM the remote machine.

"DOH!" - as @edolstra or @rbvermaa would call it... and good d^Hnight.

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