Extract locale country code for variations on first run

Author: DJAndries

chromium_src/chrome/browser/metrics/chrome_feature_list_creator.cc

@@ -0,0 +1,17 @@
+// Copyright (c) 2025 The Brave Authors. All rights reserved.
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#include "base/strings/string_util.h"
+#include "brave/components/l10n/common/locale_util.h"
+
+#define BRAVE_CHROME_FEATURE_LIST_CREATOR_SETUP_INITIAL_PREFS                                  \
+  if (!compressed_variations_seed.empty()) {                                                   \
+    local_state_->SetString(variations::prefs::kVariationsCountry,                             \
+                            base::ToLowerASCII(brave_l10n::GetDefaultISOCountryCodeString())); \
+  }
+
+#include "src/chrome/browser/metrics/chrome_feature_list_creator.cc"
+
+#undef BRAVE_CHROME_FEATURE_LIST_CREATOR_SETUP_INITIAL_PREFS

patches/chrome-browser-metrics-chrome_feature_list_creator.cc.patch

@@ -0,0 +1,12 @@
+diff --git a/chrome/browser/metrics/chrome_feature_list_creator.cc b/chrome/browser/metrics/chrome_feature_list_creator.cc
+index 73c9ee5a0d93a3937a95c3fb0da6992ef0cea567..809863891726b1ed22dedee8a92968bf5f0594d4 100644
+--- a/chrome/browser/metrics/chrome_feature_list_creator.cc
++++ b/chrome/browser/metrics/chrome_feature_list_creator.cc
+@@ -351,5 +351,7 @@ void ChromeFeatureListCreator::SetupInitialPrefs() {
+     local_state_->SetInt64(variations::prefs::kVariationsSeedDate,
+                            base::Time::Now().ToInternalValue());
+   }
++
++  BRAVE_CHROME_FEATURE_LIST_CREATOR_SETUP_INITIAL_PREFS
+ #endif  // !BUILDFLAG(IS_ANDROID) && !BUILDFLAG(IS_CHROMEOS_ASH)
+ }