(cherry picked from commit 5811b6c)

update.nix was a huuuuge hack, abusing checksum collisions, etc., and
was extremely difficult to read and maintain, especially because
values from update.nix were also used in the derivations themselves!

I've replaced this with an implementation in Python, which I chose for
readability.  Rather than generating Nix, I chose to
generate JSON, since Python can do that in the standard library and
Nix can read it.

I also set update.py as an updateScript, so Chromium can now
automatically be updated!

Fixes: NixOS#89635
(cherry picked from commit de69b70)

(cherry picked from commit 6c92847)

…churl

(cherry picked from commit 2927a19)

This is required for certain URIs that require launching external
programs (e.g. mailto:, magnet:, or irc:) or setting the default browser
via xdg-settings.
Fix NixOS#96897 and fix NixOS#92751.

(cherry picked from commit 1fa610b)

https://chromereleases.googleblog.com/2020/09/stable-channel-update-for-desktop.html

This update includes 5 security fixes.

CVEs:
CVE-2020-6573 CVE-2020-6574 CVE-2020-6575 CVE-2020-6576 CVE-2020-15959

(cherry picked from commit a9c7851)

This makes Git diffs way easier to read.
Using sort_keys=True is usually better but with this implementation the
output is a bit nicer to read IMO.

(cherry picked from commit ceb3acf)

(cherry picked from commit e249bac)

https://chromereleases.googleblog.com/2020/09/stable-channel-update-for-desktop_21.html

This update includes 10 security fixes.

CVEs:
CVE-2020-15960 CVE-2020-15961 CVE-2020-15962 CVE-2020-15963
CVE-2020-15965 CVE-2020-15966 CVE-2020-15964

(cherry picked from commit d1a27a5)