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

ios/web/web_state/ui/crw_web_controller.mm

Index: ios/web/web_state/ui/crw_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_web_controller.mm b/ios/web/web_state/ui/crw_web_controller.mm
index 4fa18a5f8fe7862594593a4d479b67f012f11880..abd0cd1ef92623d38ae1b7bee0a8b0c07c33963b 100644
--- a/ios/web/web_state/ui/crw_web_controller.mm
+++ b/ios/web/web_state/ui/crw_web_controller.mm
@@ -2844,7 +2844,7 @@ const NSTimeInterval kSnapshotOverlayTransition = 0.5;
     return NO;
   }
   std::vector<std::string> federations;
-  for (auto federation_value : *federations_value) {
+  for (const auto& federation_value : *federations_value) {
     std::string federation;
     if (!federation_value->GetAsString(&federation)) {
       DLOG(WARNING) << "JS message parameter 'federations' contains wrong type";