Get the target field index when transitioning.

src/objects.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 1608 matching lines @@
       Handle<JSObject> object,
       Handle<String> key,
       Handle<Object> value,
       PropertyAttributes attributes);
 
   // Try to follow an existing transition to a field with attributes NONE. The
   // return value indicates whether the transition was successful.
   static inline bool TryTransitionToField(Handle<JSObject> object,
                                           Handle<String> key);
 
+  inline int LastAddedFieldIndex();
+
   // Extend the receiver with a single fast property appeared first in the
   // passed map. This also extends the property backing store if necessary.
   static void AddFastPropertyUsingMap(Handle<JSObject> object, Handle<Map> map);
   inline MUST_USE_RESULT MaybeObject* AddFastPropertyUsingMap(Map* map);
 
   // Can cause GC.
   MUST_USE_RESULT MaybeObject* SetLocalPropertyIgnoreAttributes(
       String* key,
       Object* value,
       PropertyAttributes attributes);
@@ skipping 7314 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_