chromium: 67.0.3396.87 -> 68.0.3440.75 (18.03 backport)

[YorikSar]

Motivation for this change

New major version is out, so we need to backport all changes to 18.03 to get it there. This PR includes PR #43539 and PR #44132 cherry-picked to release-18.03 branch.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

I've checked only stable branch because of reasons in PR #44132

---

CC @bendlas @7c6f434c