Wrote functions to convert collections and maps to strings and invoked

corelib/src/implementation/hash_map_set.dart

Index: corelib/src/implementation/hash_map_set.dart
===================================================================
--- corelib/src/implementation/hash_map_set.dart	(revision 4412)
+++ corelib/src/implementation/hash_map_set.dart	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
@@ -268,6 +268,10 @@
     }
     return false;
   }
+
+  String toString() {
+    return Maps.mapToString(this);
+  }
 }
 
 class HashSetImplementation<E extends Hashable> implements HashSet<E> {
@@ -376,6 +380,10 @@
     return new HashSetIterator<E>(this);
   }
 
+  String toString() {
+    return Collections.collectionToString(this);
+  }
+
   // The map backing this set. The associations in this map are all
   // of the form element -> element. If a value is not in the map,
   // then it is not in the set.