Grouping all map creation code.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 6dd2a99518753b694a64e44b9848d0c9713a4935..feca2719f3481c59feb9c8c712be07af03e67593 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -3653,12 +3653,12 @@ void Map::SetBackPointer(Object* value, WriteBarrierMode mode) {
   ASSERT((value->IsUndefined() && GetBackPointer()->IsMap()) ||
          (value->IsMap() && GetBackPointer()->IsUndefined()));
   Object* object = READ_FIELD(this, kInstanceDescriptorsOrBackPointerOffset);
-  if (object->IsMap()) {
+  if (object->IsDescriptorArray()) {
+    DescriptorArray::cast(object)->set_back_pointer_storage(value);
+  } else {
     WRITE_FIELD(this, kInstanceDescriptorsOrBackPointerOffset, value);
     CONDITIONAL_WRITE_BARRIER(
         GetHeap(), this, kInstanceDescriptorsOrBackPointerOffset, value, mode);
-  } else {
-    DescriptorArray::cast(object)->set_back_pointer_storage(value);
   }
 }
 
@@ -4301,7 +4301,7 @@ MaybeObject* JSFunction::set_initial_map_and_cache_transitions(
       Map* new_map;
       ElementsKind next_kind = GetFastElementsKindFromSequenceIndex(i);
       MaybeObject* maybe_new_map =
-          current_map->CreateNextElementsTransition(next_kind);
+          current_map->CopyAsElementsKind(next_kind, INSERT_TRANSITION);
       if (!maybe_new_map->To(&new_map)) return maybe_new_map;
       maps->set(next_kind, new_map);
       current_map = new_map;