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

src/runtime.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_RUNTIME_H_
 #define V8_RUNTIME_H_
 
 #include "allocation.h"
 #include "zone.h"
 
@@ skipping 801 matching lines @@
       Handle<Object> object,
       Handle<Object> key,
       Handle<Object> value,
       PropertyAttributes attr,
       StrictMode strict_mode);
 
   MUST_USE_RESULT static MaybeHandle<Object> ForceSetObjectProperty(
       Handle<JSObject> object,
       Handle<Object> key,
       Handle<Object> value,
-      PropertyAttributes attr);
+      PropertyAttributes attr,
+      JSReceiver::StoreFromKeyed store_from_keyed
+        = JSReceiver::MAY_BE_STORE_FROM_KEYED);
 
   MUST_USE_RESULT static MaybeHandle<Object> DeleteObjectProperty(
       Isolate* isolate,
       Handle<JSReceiver> object,
       Handle<Object> key,
       JSReceiver::DeleteMode mode);
 
   MUST_USE_RESULT static MaybeHandle<Object> HasObjectProperty(
       Isolate* isolate,
       Handle<JSReceiver> object,
@@ skipping 55 matching lines @@
 class AllocateDoubleAlignFlag:  public BitField<bool,            0, 1> {};
 class AllocateTargetSpace:      public BitField<AllocationSpace, 1, 3> {};
 
 class DeclareGlobalsEvalFlag:   public BitField<bool,       0, 1> {};
 class DeclareGlobalsNativeFlag: public BitField<bool,       1, 1> {};
 class DeclareGlobalsStrictMode: public BitField<StrictMode, 2, 1> {};
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_