feat(ops/nixos/nugget): Add chromium with VAAPI patches

These patches enable hardware-accelerated video decoding, which is
useful for Stadia.

The main issue with this is that Hydra doesn't currently cache
Chromium with these patches, which means that it is built from scratch
which takes in the order of 5 hours on an otherwise unused nugget.

ops/nixos/nugget/default.nix

@@ -96,8 +96,9 @@ in depot.lib.fix(self: {
       lieer
       nuggetEmacs
       ops.kontemplate
-      third_party.git
+      third_party.chromiumVaapi
       third_party.ffmpeg
+      third_party.git
     ]) ++
 
     # programs from nixpkgs
@@ -105,7 +106,6 @@ in depot.lib.fix(self: {
       age
       bat
       cachix
-      chromium
       clang-manpages
       clang-tools
       clang_9

third_party/default.nix

@@ -125,4 +125,10 @@ in exposed // {
 
   # Make NixOS available
   nixos = import "${nixpkgsSrc}/nixos";
+
+  # Build a Chromium with VAAPI (hardware-accelerated video decoding)
+  # enabled. This is useful for Stadia on desktop.
+  chromiumVaapi = nixpkgs.chromium.override {
+    useVaapi = true;
+  };
 }