Make __proto__ a foreign callback on Object.prototype.

test/mjsunit/json.js

 // Copyright 2009 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 435 matching lines @@
 oddball2.__proto__ = { __proto__: null,
                        toJSON: function () { return oddball3; } }
 assertEquals('"true"', JSON.stringify(oddball2));
 
 
 var falseNum = Object("37");
 falseNum.__proto__ = Number.prototype;
 falseNum.toString = function() { return 42; };
 assertEquals('"42"', JSON.stringify(falseNum));
 
-// We don't currently allow plain properties called __proto__ in JSON
-// objects in JSON.parse. Instead we read them as we would JS object
-// literals. If we change that, this test should change with it.
-//
-// Parse a non-object value as __proto__. This must not create a
-// __proto__ property different from the original, and should not
-// change the original.
-var o = JSON.parse('{"__proto__":5}');
-assertEquals(Object.prototype, o.__proto__);  // __proto__ isn't changed.
-assertEquals(0, Object.keys(o).length);  // __proto__ isn't added as enumerable.
+// Parse an object value as __proto__.
+var o1 = JSON.parse('{"__proto__":[]}');
+assertEquals([], o1.__proto__);
+assertEquals(["__proto__"], Object.keys(o1));
+assertEquals([], Object.getOwnPropertyDescriptor(o1, "__proto__").value);
+assertEquals(["__proto__"], Object.getOwnPropertyNames(o1));
+assertTrue(o1.hasOwnProperty("__proto__"));
+assertTrue(Object.prototype.isPrototypeOf(o1));
+
+// Parse a non-object value as __proto__.
+var o2 = JSON.parse('{"__proto__":5}');
+assertEquals(5, o2.__proto__);
+assertEquals(["__proto__"], Object.keys(o2));
+assertEquals(5, Object.getOwnPropertyDescriptor(o2, "__proto__").value);
+assertEquals(["__proto__"], Object.getOwnPropertyNames(o2));
+assertTrue(o2.hasOwnProperty("__proto__"));
+assertTrue(Object.prototype.isPrototypeOf(o2));
 
 var json = '{"stuff before slash\\\\stuff after slash":"whatever"}';
 assertEquals(json, JSON.stringify(JSON.parse(json)));