Remember and reuse derived map for external arrays

src/property.h

 // Copyright 2006-2008 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 92 matching lines @@
 // A pointer from a map to the new map that is created by adding
 // a named property.  These are key to the speed and functioning of V8.
 // The two maps should always have the same prototype, since
 // MapSpace::CreateBackPointers depends on this.
 class MapTransitionDescriptor: public Descriptor {
  public:
   MapTransitionDescriptor(String* key, Map* map, PropertyAttributes attributes)
       : Descriptor(key, map, attributes, MAP_TRANSITION) { }
 };
 
+class ExternalArrayTransitionDescriptor: public Descriptor {
+ public:
+  ExternalArrayTransitionDescriptor(String* key,
+                                    Map* map,
+                                    ExternalArrayType array_type)
+      : Descriptor(key, map, PropertyDetails(NONE,
+                                             EXTERNAL_ARRAY_TRANSITION,
+                                             array_type)) { }
+};
+
 // Marks a field name in a map so that adding the field is guaranteed
 // to create a FIELD descriptor in the new map.  Used after adding
 // a constant function the first time, creating a CONSTANT_FUNCTION
 // descriptor in the new map.  This avoids creating multiple maps with
 // the same CONSTANT_FUNCTION field.
 class ConstTransitionDescriptor: public Descriptor {
  public:
   explicit ConstTransitionDescriptor(String* key, Map* map)
       : Descriptor(key, map, NONE, CONSTANT_TRANSITION) { }
 };
@@ skipping 132 matching lines @@
       }
       case CONSTANT_FUNCTION:
         return GetConstantFunction();
       default:
         return Smi::FromInt(0);
     }
   }
 
   Map* GetTransitionMap() {
     ASSERT(lookup_type_ == DESCRIPTOR_TYPE);
-    ASSERT(type() == MAP_TRANSITION || type() == CONSTANT_TRANSITION);
+    ASSERT(type() == MAP_TRANSITION || type() == CONSTANT_TRANSITION ||
+           type() == EXTERNAL_ARRAY_TRANSITION);
     return Map::cast(GetValue());
   }
 
   Map* GetTransitionMapFromMap(Map* map) {
     ASSERT(lookup_type_ == DESCRIPTOR_TYPE);
     ASSERT(type() == MAP_TRANSITION);
     return Map::cast(map->instance_descriptors()->GetValue(number_));
   }
 
   int GetFieldIndex() {
@@ skipping 52 matching lines @@
   JSObject* holder_;
   int number_;
   bool cacheable_;
   PropertyDetails details_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROPERTY_H_