chromium: Update all channels to latest versions.

Overview of the updated versions:

stable: 40.0.2214.91 -> 40.0.2214.115
beta:   41.0.2272.16 -> 41.0.2272.64
dev:    41.0.2272.16 -> 42.0.2305.3

Introduces 42.0.2305.3 as the new dev version, which no longer requires
our user namespaces sandbox patch. Thanks to everyone participating in
https://crbug.com/312380

 for finally having this upstream.

In the course of supporting the official namespace sandbox (that's what
the user namespace sandbox is called), a few things needed to be fixed
for version 42:

 * Add an updated nix_plugin_paths.patch, because the old
   one tries to patch the path for libpdf, which is now natively included
   in Chromium.

 * Don't copy libpdf.so to libexec path for version 42, it's no longer
   needed as it's completely built-in now.

 * Disable SUID sandbox directly in the source instead of going the easy
   route of passing --disable-setuid-sandbox. The reason is that with
   the command line flag a nasty nagbar will appear.

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