Remember and reuse derived map for external arrays

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 01073ca7b08bd272520e1b1009d266a671411e7e..643727d017f007d6be7488f99c8cb024c7055415 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -2758,21 +2758,6 @@ MaybeObject* Map::GetSlowElementsMap() {
 }
 
 
-MaybeObject* Map::NewExternalArrayElementsMap() {
-  // TODO(danno): Special case empty object map (or most common case)
-  // to return a pre-canned pixel array map.
-  Object* obj;
-  { MaybeObject* maybe_obj = CopyDropTransitions();
-    if (!maybe_obj->ToObject(&obj)) return maybe_obj;
-  }
-  Map* new_map = Map::cast(obj);
-  new_map->set_has_fast_elements(false);
-  new_map->set_has_external_array_elements(true);
-  Counters::map_to_external_array_elements.Increment();
-  return new_map;
-}
-
-
 ACCESSORS(Map, instance_descriptors, DescriptorArray,
           kInstanceDescriptorsOffset)
 ACCESSORS(Map, code_cache, Object, kCodeCacheOffset)