chromium: Update stable and beta channels.

These new versions are introduced with this commit:

stable: 26.0.1410.63 -> 27.0.1453.93 (builds fine, tested)
beta:   27.0.1453.81 -> 28.0.1500.20 (builds fine, tested)

Unfortunately the tarball for the dev version 29.0.1530.2 isn't available at the
moment, so we're going to update it later.

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