Promoting elements transitions to their own field.

src/ia32/macro-assembler-ia32.cc

 // 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 486 matching lines @@
                                 Label* early_success,
                                 CompareMapMode mode) {
   cmp(FieldOperand(obj, HeapObject::kMapOffset), map);
   if (mode == ALLOW_ELEMENT_TRANSITION_MAPS) {
     ElementsKind kind = map->elements_kind();
     if (IsFastElementsKind(kind)) {
       bool packed = IsFastPackedElementsKind(kind);
       Map* current_map = *map;
       while (CanTransitionToMoreGeneralFastElementsKind(kind, packed)) {
         kind = GetNextMoreGeneralFastElementsKind(kind, packed);
-        current_map = current_map->LookupElementsTransitionMap(kind, NULL);
+        current_map = current_map->LookupElementsTransitionMap(kind);
         if (!current_map) break;
         j(equal, early_success, Label::kNear);
         cmp(FieldOperand(obj, HeapObject::kMapOffset),
             Handle<Map>(current_map));
       }
     }
   }
 }
 
 
@@ skipping 2304 matching lines @@
   // Load the prototype from the map and loop if non-null.
   bind(&check_prototype);
   mov(ecx, FieldOperand(ebx, Map::kPrototypeOffset));
   cmp(ecx, isolate()->factory()->null_value());
   j(not_equal, &next);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32