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

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 f982a66bc428227d2aaf3fb2ae24dc30fc0bcfaf..f94ab75e9a84d2cf0d819510782b23a660057bcc 100644
--- a/test/mjsunit/harmony/object-observe.js
+++ b/test/mjsunit/harmony/object-observe.js
@@ -286,6 +286,20 @@ 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);