chromium: Add another mirror for Chrome deb.

The only mirror left which still has the .deb for 44.0.2403.89 is
http://mirror.pcbeta.com/

, but that one doesn't seem to be reachable
from certain contries.

And according to @CestDiego, it doesn't seem to be reachable from within
the US.

Closes #9021, thanks to @CestDiego for reporting.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Reported-by: Diego Berrocal <cestdiego@gmail.com>
Tested-by: Diego Berrocal <cestdiego@gmail.com>