Object.defineProperty shouldn't be a hint that we're constructing a dictionary.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 42f27641adf1396910892ef0e1dbcab3cd9b5640..fee0629542b001d850ad93d26b17aee5ff1ad12f 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2249,7 +2249,8 @@ class JSObject: public JSReceiver {
       PropertyAttributes attributes,
       ValueType value_type = OPTIMAL_REPRESENTATION,
       StoreMode mode = ALLOW_AS_CONSTANT,
-      ExtensibilityCheck extensibility_check = PERFORM_EXTENSIBILITY_CHECK);
+      ExtensibilityCheck extensibility_check = PERFORM_EXTENSIBILITY_CHECK,
+      StoreFromKeyed store_mode = MAY_BE_STORE_FROM_KEYED);
 
   static inline Handle<String> ExpectedTransitionKey(Handle<Map> map);
   static inline Handle<Map> ExpectedTransitionTarget(Handle<Map> map);