Revert 13878

lib/coreimpl/collections.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * The [Collections] class implements static methods useful when
  * writing a class that implements [Collection] and the [iterator]
  * method.
  */
 class Collections {
@@ skipping 137 matching lines @@
       result.add(o);
     }
   }
 
   /**
    * Returns true if the specified collection contains the specified object
    * reference.
    */
   static _containsRef(Collection c, Object ref) {
     for (var e in c) {
-      if (identical(e, ref)) return true;
+      if (e === ref) return true;
     }
     return false;
   }
 }