Prevent changes to hidden properties from being observable via Object.observe

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 268 matching lines @@
 reset();
 var obj = {};
 Object.getNotifier(obj);
 Object.observe(obj, observer.callback);
 obj.id = 1;
 Object.deliverChangeRecords(observer.callback);
 observer.assertCallbackRecords([
   { object: obj, type: 'new', name: 'id' },
 ]);
 
+// The empty-string property is observable
+reset();
+var obj = {};
+Object.observe(obj, observer.callback);
+obj[''] = '';
+obj[''] = ' ';
+delete obj[''];
+Object.deliverChangeRecords(observer.callback);
+observer.assertCallbackRecords([
+  { object: obj, type: 'new', name: '' },
+  { object: obj, type: 'updated', name: '', oldValue: '' },
+  { object: obj, type: 'deleted', name: '', oldValue: ' ' },
+]);
+
 // Observing a continuous stream of changes, while itermittantly unobserving.
 reset();
 Object.observe(obj, observer.callback);
 Object.getNotifier(obj).notify({
   type: 'updated',
   val: 1
 });
 
 Object.unobserve(obj, observer.callback);
 Object.getNotifier(obj).notify({
@@ skipping 1316 matching lines @@
     for (var n1 = 0; n1 < 3; ++n1)
       for (var n2 = 0; n2 < 3; ++n2)
         for (var i in mutation)
           TestFastElementsLength(mutation[i], b1 != 0, b2 != 0, 20*n1, 20*n2);
 
 for (var b1 = 0; b1 < 2; ++b1)
   for (var b2 = 0; b2 < 2; ++b2)
     for (var n = 0; n < 3; ++n)
       for (var i in mutationByIncr)
         TestFastElementsLength(mutationByIncr[i], b1 != 0, b2 != 0, 7*n, 7*n+1);