Directly store the transition target on LookupResult in TransitionResult.

src/transitions-inl.h

 // 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 142 matching lines @@
     ASSERT(transition_number == kSimpleTransitionIndex);
     return set(kSimpleTransitionTarget, value);
   }
   ASSERT(transition_number < number_of_transitions());
   set(ToTargetIndex(transition_number), value);
 }
 
 
 PropertyDetails TransitionArray::GetTargetDetails(int transition_number) {
   Map* map = GetTarget(transition_number);
-  DescriptorArray* descriptors = map->instance_descriptors();
-  int descriptor = map->LastAdded();
-  return descriptors->GetDetails(descriptor);
+  return map->GetLastDescriptorDetails();
 }
 
 
 int TransitionArray::Search(Name* name) {
   if (IsSimpleTransition()) {
     Name* key = GetKey(kSimpleTransitionIndex);
     if (key->Equals(name)) return kSimpleTransitionIndex;
     return kNotFound;
   }
   return internal::Search<ALL_ENTRIES>(this, name);
@@ skipping 11 matching lines @@
 
 
 #undef FIELD_ADDR
 #undef WRITE_FIELD
 #undef CONDITIONAL_WRITE_BARRIER
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TRANSITIONS_INL_H_