nixos/chromium: add the ability to set initial preferences

nixos/modules/programs/chromium.nix

···
           }
         '';
       };
+
+      initialPrefs = mkOption {
+        type = types.attrs;
+        description = lib.mdDoc ''
+          Initial preferences are used to configure the browser for the first run.
+          Unlike {option}`programs.chromium.extraOpts`, initialPrefs can be changed by users in the browser settings.
+          More information can be found in the Chromium documentation:
+          <https://www.chromium.org/administrators/configuring-other-preferences/>
+        '';
+        default = {};
+        example = literalExpression ''
+          {
+            "first_run_tabs" = [
+              "https://nixos.org/"
+            ];
+          }
+        '';
+      };
     };
   };
 
···
         { source = "${cfg.plasmaBrowserIntegrationPackage}/etc/chromium/native-messaging-hosts/org.kde.plasma.browser_integration.json"; };
       "chromium/policies/managed/default.json" = lib.mkIf (defaultProfile != {}) { text = builtins.toJSON defaultProfile; };
       "chromium/policies/managed/extra.json" = lib.mkIf (cfg.extraOpts != {}) { text = builtins.toJSON cfg.extraOpts; };
+      "chromium/initial_preferences" = lib.mkIf (cfg.initialPrefs != {}) { text = builtins.toJSON cfg.initialPrefs; };
       # for google-chrome https://www.chromium.org/administrators/linux-quick-start
       "opt/chrome/native-messaging-hosts/org.kde.plasma.browser_integration.json" = lib.mkIf cfg.enablePlasmaBrowserIntegration
         { source = "${cfg.plasmaBrowserIntegrationPackage}/etc/opt/chrome/native-messaging-hosts/org.kde.plasma.browser_integration.json"; };

pkgs/applications/networking/browsers/chromium/common.nix

···
       # (we currently package 1.26 in Nixpkgs while Chromium bundles 1.21):
       # Source: https://bugs.chromium.org/p/angleproject/issues/detail?id=7582#c1
       ./patches/angle-wayland-include-protocol.patch
+      # Chromium reads initial_preferences from its own executable directory
+      # This patch modifies it to read /etc/chromium/initial_preferences
+      ./patches/chromium-initial-prefs.patch
     ] ++ lib.optionals (chromiumVersionAtLeast "120") [
       # We need to revert this patch to build M120+ with LLVM 17:
       ./patches/chromium-120-llvm-17.patch

pkgs/applications/networking/browsers/chromium/patches/chromium-initial-prefs.patch

···
+diff --git a/chrome/browser/first_run/first_run_internal_linux.cc b/chrome/browser/first_run/first_run_internal_linux.cc
+index 33fd579012..9a17b54b37 100644
+--- a/chrome/browser/first_run/first_run_internal_linux.cc
++++ b/chrome/browser/first_run/first_run_internal_linux.cc
+@@ -19,13 +19,7 @@ bool IsOrganicFirstRun() {
+ }
+ 
+ base::FilePath InitialPrefsPath() {
+-  // The standard location of the initial prefs is next to the chrome binary.
+-  base::FilePath dir_exe;
+-  if (!base::PathService::Get(base::DIR_EXE, &dir_exe)) {
+-    return base::FilePath();
+-  }
+-
+-  return installer::InitialPreferences::Path(dir_exe);
++  return base::FilePath("/etc/chromium/initial_preferences");
+ }
+ 
+ }  // namespace internal