Ensure callbacks transitions are actually followed.

src/objects.cc

 // Copyright 2013 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 5372 matching lines @@
 
 
 MaybeObject* JSObject::DefineFastAccessor(Name* name,
                                           AccessorComponent component,
                                           Object* accessor,
                                           PropertyAttributes attributes) {
   ASSERT(accessor->IsSpecFunction() || accessor->IsUndefined());
   LookupResult result(GetIsolate());
   LocalLookup(name, &result);
 
-  if (result.IsFound()
-      && !result.IsPropertyCallbacks()
-      && !result.IsTransition()) return GetHeap()->null_value();
+  if (result.IsFound() && !result.IsPropertyCallbacks()) {
+    return GetHeap()->null_value();
+  }
 
   // Return success if the same accessor with the same attributes already exist.
   AccessorPair* source_accessors = NULL;
   if (result.IsPropertyCallbacks()) {
     Object* callback_value = result.GetCallbackObject();
     if (callback_value->IsAccessorPair()) {
       source_accessors = AccessorPair::cast(callback_value);
       Object* entry = source_accessors->get(component);
       if (entry == accessor && result.GetAttributes() == attributes) {
         return this;
@@ skipping 9099 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal