Make __proto__ a foreign callback on Object.prototype.

src/property.h

 // Copyright 2012 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 183 matching lines @@
     number_ = number;
   }
 
   void TransitionResult(JSObject* holder, int number) {
     lookup_type_ = TRANSITION_TYPE;
     details_ = PropertyDetails(NONE, TRANSITION);
     holder_ = holder;
     number_ = number;
   }
 
-  void ConstantResult(JSObject* holder) {
-    lookup_type_ = CONSTANT_TYPE;
-    holder_ = holder;
-    details_ =
-        PropertyDetails(static_cast<PropertyAttributes>(DONT_ENUM |
-                                                        DONT_DELETE),
-                        CALLBACKS);
-    number_ = -1;
-  }
-
   void DictionaryResult(JSObject* holder, int entry) {
     lookup_type_ = DICTIONARY_TYPE;
     holder_ = holder;
     details_ = holder->property_dictionary()->DetailsAt(entry);
     number_ = entry;
   }
 
   void HandlerResult(JSProxy* proxy) {
     lookup_type_ = HANDLER_TYPE;
     holder_ = proxy;
@@ skipping 196 matching lines @@
     ASSERT(type() == CONSTANT_FUNCTION);
     return JSFunction::cast(GetValue());
   }
 
   JSFunction* GetConstantFunctionFromMap(Map* map) {
     ASSERT(type() == CONSTANT_FUNCTION);
     return JSFunction::cast(GetValueFromMap(map));
   }
 
   Object* GetCallbackObject() {
-    if (lookup_type_ == CONSTANT_TYPE) {
-      return HEAP->prototype_accessors();
-    }
-    ASSERT(!IsTransition());
+    ASSERT(type() == CALLBACKS && !IsTransition());
     return GetValue();
   }
 
 #ifdef OBJECT_PRINT
   void Print(FILE* out);
 #endif
 
   Object* GetValue() {
     if (lookup_type_ == DESCRIPTOR_TYPE) {
       return GetValueFromMap(holder()->map());
@@ skipping 15 matching lines @@
   Isolate* isolate_;
   LookupResult* next_;
 
   // Where did we find the result;
   enum {
     NOT_FOUND,
     DESCRIPTOR_TYPE,
     TRANSITION_TYPE,
     DICTIONARY_TYPE,
     HANDLER_TYPE,
-    INTERCEPTOR_TYPE,
-    CONSTANT_TYPE
+    INTERCEPTOR_TYPE
   } lookup_type_;
 
   JSReceiver* holder_;
   int number_;
   bool cacheable_;
   PropertyDetails details_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROPERTY_H_