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

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include "allocation.h"
 #include "assert-scope.h"
 #include "builtins.h"
@@ skipping 2231 matching lines @@
       StrictMode strict_mode,
       StoreFromKeyed store_mode = MAY_BE_STORE_FROM_KEYED);
 
   MUST_USE_RESULT static MaybeHandle<Object> SetLocalPropertyIgnoreAttributes(
       Handle<JSObject> object,
       Handle<Name> key,
       Handle<Object> value,
       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);
 
   // Try to follow an existing transition to a field with attributes NONE. The
   // return value indicates whether the transition was successful.
   static inline Handle<Map> FindTransitionToField(Handle<Map> map,
                                                   Handle<Name> key);
 
   // Extend the receiver with a single fast property appeared first in the
@@ skipping 8910 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_