Add bit_field3 to Map objects

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index b82c76aa830bcb249f919419e99e46b2c6f7410e..160dba8d49d85a60ee4ec4d59ff1ccb42bc7e474 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -1081,8 +1081,13 @@ void MarkCompactCollector::MarkMapContents(Map* map) {
   FixedArray* prototype_transitions = map->unchecked_prototype_transitions();
   if (!prototype_transitions->IsMarked()) SetMark(prototype_transitions);
 
-  MarkDescriptorArray(reinterpret_cast<DescriptorArray*>(
-      *HeapObject::RawField(map, Map::kInstanceDescriptorsOffset)));
+  Object* raw_descriptor_array =
+      *HeapObject::RawField(map,
+                            Map::kInstanceDescriptorsOrBitField3Offset);
+  if (!raw_descriptor_array->IsSmi()) {
+    MarkDescriptorArray(
+        reinterpret_cast<DescriptorArray*>(raw_descriptor_array));
+  }
 
   // Mark the Object* fields of the Map.
   // Since the descriptor array has been marked already, it is fine