chromium: 68.0.3440.106 -> 69.0.3497.81

[YorikSar]

Also update to build with external gn.

Motivation for this change

Chromium 69 is out, with new looks and 40 security fixes.

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.

---

CC @vcunat @bendlas @7c6f434c

[YorikSar]

Note that it is currently build with older version of gn that is currently in packages (and it works), I've posted gn update at #46328 but it looks like we can backport without it.

[vcunat]

For 18.03 this won't build if cherry-picked directly, unless I did something wrong during conflict resolution.

  configuring
  ERROR at //ui/events/BUILD.gn:80:12: Assignment had no effect.
    friend = [ ":*" ]
             ^------
  You set the variable "friend" here and it was unused before it went
  out of scope.
  See //BUILD.gn:211:7: which caused the file to be included.
        "//ui/events:events_unittests",
        ^-----------------------------

(security fixes means we probably should do it)

[YorikSar]

@vcunat I've ran into same issue, investigating it.

[YorikSar]

@vcunat the problem is in gn version. Sad thing is that if we backport changes to it, it'll trigger huge rebuild. Will it be ok if we import newer gn just for chromium?

[YorikSar]

Posted new PR with backport with new private gn version.