Make sure builtin functions don't rely on __proto__.

src/objects.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 4834 matching lines @@
   inline void set_non_instance_prototype(bool value);
   inline bool has_non_instance_prototype();
 
   // Tells whether function has special prototype property. If not, prototype
   // property will not be created when accessed (will return undefined),
   // and construction from this function will not be allowed.
   inline void set_function_with_prototype(bool value);
   inline bool function_with_prototype();
 
   // Tells whether the instance with this map should be ignored by the
-  // __proto__ accessor.
+  // Object.getPrototypeOf() function and the __proto__ accessor.
   inline void set_is_hidden_prototype() {
     set_bit_field(bit_field() | (1 << kIsHiddenPrototype));
   }
 
   inline bool is_hidden_prototype() {
     return ((1 << kIsHiddenPrototype) & bit_field()) != 0;
   }
 
   // Records and queries whether the instance has a named interceptor.
   inline void set_has_named_interceptor() {
@@ skipping 4203 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_