move cookie list override logic to account for uninitialized preferences

The previous implementation only iterated through lists that existed in
the preferences already, so in practice it would only override lists
that had `enabled: false` - i.e. lists that had been enabled and
disabled again before the "touched" preference was introduced.

This fix clones the preferences dictionary and adds the cookie list with
`enabled: true` to the cloned dictionary if the override should occur.

components/brave_shields/browser/ad_block_regional_service_manager.cc

@@ -70,18 +70,24 @@ void AdBlockRegionalServiceManager::StartRegionalServices() {
   base::AutoLock lock(regional_services_lock_);
   const base::DictionaryValue* regional_filters_dict =
       local_state->GetDictionary(prefs::kAdBlockRegionalFilters);
-  for (base::DictionaryValue::Iterator it(*regional_filters_dict);
-       !it.IsAtEnd(); it.Advance()) {
-    const std::string uuid = it.key();
+
+  base::Value regional_filters_dict_with_cookielist =
+      base::Value(regional_filters_dict->Clone());
+  if (base::FeatureList::IsEnabled(kBraveAdblockCookieListDefault) &&
+      !cookie_list_touched) {
+    auto cookie_list_entry = base::Value(base::Value::Type::DICTIONARY);
+    cookie_list_entry.SetBoolKey("enabled", true);
+    regional_filters_dict_with_cookielist.SetKey(kCookieListUuid,
+                                                 std::move(cookie_list_entry));
+  }
+
+  for (const auto kv : regional_filters_dict_with_cookielist.DictItems()) {
+    const std::string uuid = kv.first;
     bool enabled = false;
-    const base::DictionaryValue* regional_filter_dict = nullptr;
-    regional_filters_dict->GetDictionary(uuid, &regional_filter_dict);
-    if (uuid == kCookieListUuid &&
-        base::FeatureList::IsEnabled(kBraveAdblockCookieListDefault) &&
-        !cookie_list_touched) {
-      enabled = true;
-    } else if (regional_filter_dict) {
-      regional_filter_dict->GetBoolean("enabled", &enabled);
+    const base::Value* regional_filter_dict =
+        regional_filters_dict_with_cookielist.FindDictKey(uuid);
+    if (regional_filter_dict) {
+      enabled = regional_filter_dict->FindBoolKey("enabled").value_or(false);
     }
     if (enabled) {
       auto catalog_entry = brave_shields::FindAdBlockFilterListByUUID(