Do not follow accessor map transitions when marking descriptor arrays.

src/mark-compact-inl.h

Index: src/mark-compact-inl.h
diff --git a/src/mark-compact-inl.h b/src/mark-compact-inl.h
index 64faf82dad7d773a51d91406ca5f99af706d8be4..a9107bd277fdbdabf0e891f79a3c2655c786d8e7 100644
--- a/src/mark-compact-inl.h
+++ b/src/mark-compact-inl.h
@@ -66,6 +66,19 @@ void MarkCompactCollector::MarkObject(HeapObject* obj, MarkBit mark_bit) {
 }
 
 
+bool MarkCompactCollector::MarkObjectWithoutPush(HeapObject* object) {
+  MarkBit mark = Marking::MarkBitFrom(object);
+  bool old_mark = mark.Get();
+  if (!old_mark) SetMark(object, mark);
+  return old_mark;
+}
+
+
+void MarkCompactCollector::MarkObjectAndPush(HeapObject* object) {
+  if (!MarkObjectWithoutPush(object)) marking_deque_.PushBlack(object);
+}
+
+
 void MarkCompactCollector::SetMark(HeapObject* obj, MarkBit mark_bit) {
   ASSERT(!mark_bit.Get());
   ASSERT(Marking::MarkBitFrom(obj) == mark_bit);