Remember and reuse derived map for external arrays

src/objects-inl.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2740 matching lines @@
   { 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);
   Counters::map_fast_to_slow_elements.Increment();
   return new_map;
 }
 
 
-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)
 ACCESSORS(Map, constructor, Object, kConstructorOffset)
 
 ACCESSORS(JSFunction, shared, SharedFunctionInfo, kSharedFunctionInfoOffset)
 ACCESSORS(JSFunction, literals, FixedArray, kLiteralsOffset)
 ACCESSORS(JSFunction, next_function_link, Object, kNextFunctionLinkOffset)
 
 ACCESSORS(GlobalObject, builtins, JSBuiltinsObject, kBuiltinsOffset)
@@ skipping 1150 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_