Revert of Remove more dead code after Object.observe removal

src/js/array.js

Index: src/js/array.js
diff --git a/src/js/array.js b/src/js/array.js
index 61c21e784be40660df9b687bfbdbe5d187cc58e8..c368cf395cee0a6327350ff89971e84719a50b7a 100644
--- a/src/js/array.js
+++ b/src/js/array.js
@@ -1024,9 +1024,9 @@
   var num_non_undefined = %RemoveArrayHoles(array, length);
 
   if (num_non_undefined == -1) {
-    // There were indexed accessors in the array.
+    // The array is observed, or there were indexed accessors in the array.
     // Move array holes and undefineds to the end using a Javascript function
-    // that is safe in the presence of accessors.
+    // that is safe in the presence of accessors and is observable.
     num_non_undefined = SafeRemoveArrayHoles(array);
   }