Make __proto__ a foreign callback on Object.prototype.

test/mjsunit/harmony/object-observe.js

Index: test/mjsunit/harmony/object-observe.js
diff --git a/test/mjsunit/harmony/object-observe.js b/test/mjsunit/harmony/object-observe.js
index b7ea22e32d04c36dd3a205fe82a71d3edf75c733..07c8190e4664599b1cea5d0918eb97d50f95e09e 100644
--- a/test/mjsunit/harmony/object-observe.js
+++ b/test/mjsunit/harmony/object-observe.js
@@ -896,7 +896,7 @@ var q = {bar: 'no'};
 obj.__proto__ = p;
 obj.__proto__ = p;  // ignored
 obj.__proto__ = null;
-obj.__proto__ = q;
+obj.__proto__ = q;  // the __proto__ accessor is gone
 // TODO(adamk): Add tests for objects with hidden prototypes
 // once we support observing the global object.
 Object.deliverChangeRecords(observer.callback);
@@ -904,7 +904,7 @@ observer.assertCallbackRecords([
   { object: obj, name: '__proto__', type: 'prototype',
     oldValue: Object.prototype },
   { object: obj, name: '__proto__', type: 'prototype', oldValue: p },
-  { object: obj, name: '__proto__', type: 'prototype', oldValue: null },
+  { object: obj, name: '__proto__', type: 'new' },
 ]);