Fix map modification in transition tree traversal.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index cc70bfa8e53a1e96ade1dbf2f6f0c0b17da4a017..bafa8b3299c18dfb8a3e0cf99acbea65169ed558 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1229,9 +1229,9 @@ Map* HeapObject::map() {
 }
 
 
-void HeapObject::set_map(Map* value) {
+void HeapObject::set_map(Map* value, WriteBarrierMode mode) {
   set_map_word(MapWord::FromMap(value));
-  if (value != NULL) {
+  if (mode == UPDATE_WRITE_BARRIER && 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);