Use std::unique_ptr for base::DictionaryValue and base::ListValue's internal store.

components/ntp_snippets/ntp_snippets_service.cc

Index: components/ntp_snippets/ntp_snippets_service.cc
diff --git a/components/ntp_snippets/ntp_snippets_service.cc b/components/ntp_snippets/ntp_snippets_service.cc
index 4da4e50a3ddeb8950cafb65e3d8ba89a28e7d58b..638539f36ad99ede380d83362d941b05605c499a 100644
--- a/components/ntp_snippets/ntp_snippets_service.cc
+++ b/components/ntp_snippets/ntp_snippets_service.cc
@@ -503,7 +503,7 @@ void NTPSnippetsService::StoreDiscardedSnippetsToPrefs() {
 std::set<std::string> NTPSnippetsService::GetSnippetHostsFromPrefs() const {
   std::set<std::string> hosts;
   const base::ListValue* list = pref_service_->GetList(prefs::kSnippetHosts);
-  for (const base::Value* value : *list) {
+  for (const auto& value : *list) {
     std::string str;
     bool success = value->GetAsString(&str);
     DCHECK(success) << "Failed to parse snippet host from prefs";