Confusion on changing data property callback attributes

src/accessors.cc

 // 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.
 
 #include "v8.h"
 #include "accessors.h"
 
 #include "compiler.h"
 #include "contexts.h"
 #include "deoptimizer.h"
@@ skipping 23 matching lines @@
   info->set_prohibits_overwriting(false);
   info->set_name(*name);
   Handle<Object> get = v8::FromCData(isolate, getter);
   Handle<Object> set = v8::FromCData(isolate, setter);
   info->set_getter(*get);
   info->set_setter(*set);
   return info;
 }
 
 
+Handle<ExecutableAccessorInfo> Accessors::CloneAccessor(
+    Isolate* isolate,
+    Handle<ExecutableAccessorInfo> accessor) {
+  Factory* factory = isolate->factory();
+  Handle<ExecutableAccessorInfo> info = factory->NewExecutableAccessorInfo();
+  info->set_name(accessor->name());
+  info->set_flag(accessor->flag());
+  info->set_expected_receiver_type(accessor->expected_receiver_type());
+  info->set_getter(accessor->getter());
+  info->set_setter(accessor->setter());
+  info->set_data(accessor->data());
+  return info;
+}
+
+
 template <class C>
 static C* FindInstanceOf(Isolate* isolate, Object* obj) {
   for (Object* cur = obj; !cur->IsNull(); cur = cur->GetPrototype(isolate)) {
     if (Is<C>(cur)) return C::cast(cur);
   }
   return NULL;
 }
 
 
 static V8_INLINE bool CheckForName(Handle<String> name,
@@ skipping 1258 matching lines @@
   info->set_data(Smi::FromInt(index));
   Handle<Object> getter = v8::FromCData(isolate, &ModuleGetExport);
   Handle<Object> setter = v8::FromCData(isolate, &ModuleSetExport);
   info->set_getter(*getter);
   if (!(attributes & ReadOnly)) info->set_setter(*setter);
   return info;
 }
 
 
 } }  // namespace v8::internal