Keep prototype maps in dictionary mode until ICs see them

src/keys.cc

Index: src/keys.cc
diff --git a/src/keys.cc b/src/keys.cc
index f010d6dae84c14c4e68ed71e209e5bc1d39fe0dd..eee015075a584871fcb0aba448d63aca94601740 100644
--- a/src/keys.cc
+++ b/src/keys.cc
@@ -157,8 +157,7 @@ Maybe<bool> KeyAccumulator::CollectKeys(Handle<JSReceiver> receiver,
   PrototypeIterator::WhereToEnd end = mode_ == KeyCollectionMode::kOwnOnly
                                           ? PrototypeIterator::END_AT_NON_HIDDEN
                                           : PrototypeIterator::END_AT_NULL;
-  for (PrototypeIterator iter(isolate_, object,
-                              PrototypeIterator::START_AT_RECEIVER, end);
+  for (PrototypeIterator iter(isolate_, object, kStartAtReceiver, end);
        !iter.IsAtEnd();) {
     Handle<JSReceiver> current =
         PrototypeIterator::GetCurrent<JSReceiver>(iter);