Wrote functions to convert collections and maps to strings and invoked

runtime/lib/immutable_map.dart

 // Copyright (c) 2011, 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.
 // Immutable map class for compiler generated map literals.
 
 class ImmutableMap<K, V> implements Map<K, V> {
   final ImmutableArray kvPairs_;
 
   const ImmutableMap._create(ImmutableArray keyValuePairs)
       : kvPairs_ = keyValuePairs;
@@ skipping 70 matching lines @@
 
   void clear() {
     throw const IllegalAccessException();
   }
 
   V remove(K key) {
     throw const IllegalAccessException();
   }
 
   String toString() {
-    // TODO(srdjan): Extend text representation.
-    return "ImmutableMap";
+    return Maps.mapToString(this);
   }
 }