Wrote functions to convert collections and maps to strings and invoked

corelib/src/implementation/linked_hash_map.dart

-// 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.
 
 /**
  * This class represents a pair of two objects, used by LinkedHashMap
  * to store a {key, value} in a list.
  */
 class KeyValuePair<K, V> {
   KeyValuePair(this.key, this.value) {}
 
@@ skipping 95 matching lines @@
   }
 
   bool isEmpty() {
     return length == 0;
   }
 
   void clear() {
     _map.clear();
     _list.clear();
   }
+
+  String toString() {
+    return Maps.mapToString(this);
+  }
 }