Handle CALLBACKS with map transitions when doing GC in the map tree.

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 4652 matching lines @@
   int IndexInCodeCache(Object* name, Code* code);
 
   // Removes a code object from the code cache at the given index.
   void RemoveFromCodeCache(String* name, Code* code, int index);
 
   // For every transition in this map, makes the transition's
   // target's prototype pointer point back to this map.
   // This is undone in MarkCompactCollector::ClearNonLiveTransitions().
   void CreateBackPointers();
 
-  void CreateOneBackPointer(Map* transition_target);
+  void CreateOneBackPointer(Object* transition_target);
 
   // Set all map transitions from this map to dead maps to null.
   // Also, restore the original prototype on the targets of these
   // transitions, so that we do not process this map again while
   // following back pointers.
   void ClearNonLiveTransitions(Heap* heap, Object* real_prototype);
 
   // Computes a hash value for this map, to be used in HashTables and such.
   int Hash();
 
@@ skipping 3552 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_