chromium: Move source package into own subdir.

Next, we're going to refactor update.sh and the first step is to ensure
that we keep everything related to sources into its own subdirectory to
not clutter up the main directory too much.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
chromium: Rewrite updater into using Nix.

We're now using Nix directly for fetching sources. The first part of
update.nix contains quite a lot of impure functions, we mainly need to
avoid caching any previously fetched info from OmahaProxy.

Because of this we may need to cleanup some of this later, but right now
we have the same functionality as update.sh had before.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
chromium: HYDRA-PICKUP, don't use.

Don't evere use or merge this commit, it will vanish soon :-)

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