After assignment return right hand side value instead of undefined when Object.isExtensible(o) === …

src/objects.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1738 matching lines @@
 
 MaybeObject* JSObject::AddProperty(String* name,
                                    Object* value,
                                    PropertyAttributes attributes,
                                    StrictModeFlag strict_mode) {
   ASSERT(!IsJSGlobalProxy());
   Map* map_of_this = map();
   Heap* heap = GetHeap();
   if (!map_of_this->is_extensible()) {
     if (strict_mode == kNonStrictMode) {
-      return heap->undefined_value();
+      return value;
     } else {
       Handle<Object> args[1] = {Handle<String>(name)};
       return heap->isolate()->Throw(
           *FACTORY->NewTypeError("object_not_extensible",
                                  HandleVector(args, 1)));
     }
   }
   if (HasFastProperties()) {
     // Ensure the descriptor array does not get too big.
     if (map_of_this->instance_descriptors()->number_of_descriptors() <
@@ skipping 11301 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single break point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 
 } }  // namespace v8::internal