chromium: Propagate browser's meta to the wrapper.

We obviously don't want the Hydra job of nixpkgs to fail, so we need to
make sure that we have a proper meta attribute on the outermost
derivation.

For builds based on the Chromium source tree (like for example libcef),
we can still move the wrapper elsewhere when we need it.

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