Fix map modification in transition tree traversal.

src/objects-inl.h

 // Copyright 2011 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 1221 matching lines @@
 void HeapObject::set_map(Map* value) {
   set_map_word(MapWord::FromMap(value));
   if (value != NULL) {
     // TODO(1600) We are passing NULL as a slot because maps can never be on
     // evacuation candidate.
     value->GetHeap()->incremental_marking()->RecordWrite(this, NULL, value);
   }
 }
 
 
+// Unsafe accessor omitting write barrier.
+void HeapObject::set_map_unsafe(Map* value) {
+  set_map_word(MapWord::FromMap(value));
+}
+
+
 MapWord HeapObject::map_word() {
   return MapWord(reinterpret_cast<uintptr_t>(READ_FIELD(this, kMapOffset)));
 }
 
 
 void HeapObject::set_map_word(MapWord map_word) {
   // WRITE_FIELD does not invoke write barrier, but there is no need
   // here.
   WRITE_FIELD(this, kMapOffset, reinterpret_cast<Object*>(map_word.value_));
 }
@@ skipping 3434 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_