Make __proto__ a foreign callback on Object.prototype.

test/mjsunit/json.js

Index: test/mjsunit/json.js
diff --git a/test/mjsunit/json.js b/test/mjsunit/json.js
index 6e91725c7d85f3c2dc18034d5d524060ba10a709..79826dbef181dc6f7b467443a04080bfd5db8bce 100644
--- a/test/mjsunit/json.js
+++ b/test/mjsunit/json.js
@@ -453,16 +453,23 @@ 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)));