Object.observe: notify of __proto__ changes

test/mjsunit/harmony/object-observe.js

 // 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 792 matching lines @@
 Object.observe(dummy, observer.callback);
 Object.unobserve(dummy, observer.callback);
 var array = [0];
 Object.observe(array, observer.callback);
 array.splice(0, 1);
 Object.deliverChangeRecords(observer.callback);
 observer.assertCallbackRecords([
   { object: array, name: '0', type: 'deleted', oldValue: 0 },
   { object: array, name: 'length', type: 'updated', oldValue: 1},
 ]);
+
+// __proto__
+reset();
+var obj = {};
+Object.observe(obj, observer.callback);
+var p = {foo: 'yes'};
+var q = {bar: 'no'};
+obj.__proto__ = p;
+obj.__proto__ = p;  // ignored
+obj.__proto__ = null;
+obj.__proto__ = q;
+// TODO(adamk): Add tests for objects with hidden prototypes
+// once we support observing the global object.
+Object.deliverChangeRecords(observer.callback);
+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 },
+]);