Wrote functions to convert collections and maps to strings and invoked

corelib/src/implementation/hash_map_set.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.
 
 // Hash map implementation with open addressing and quadratic probing.
 class HashMapImplementation<K extends Hashable, V> implements HashMap<K, V> {
 
   // The [_keys] list contains the keys inserted in the map.
   // The [_keys] list must be a raw list because it
   // will contain both elements of type K, and the [_DELETED_KEY] of type
   // [_DeletedKeySentinel].
@@ skipping 249 matching lines @@
   bool containsValue(V value) {
     int length = _values.length;
     for (int i = 0; i < length; i++) {
       var key = _keys[i];
       if ((key !== null) && (key !== _DELETED_KEY)) {
         if (_values[i] == value) return true;
       }
     }
     return false;
   }
+
+  String toString() {
+    return Maps.mapToString(this);
+  }
 }
 
 class HashSetImplementation<E extends Hashable> implements HashSet<E> {
 
   HashSetImplementation() {
     _backingMap = new HashMapImplementation<E, E>();
   }
 
   factory HashSetImplementation.from(Iterable<E> other) {
     Set<E> set = new HashSetImplementation<E>();
@@ skipping 88 matching lines @@
   }
 
   int get length() {
     return _backingMap.length;
   }
 
   Iterator<E> iterator() {
     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.
   HashMapImplementation<E, E> _backingMap;
 }
 
 class HashSetIterator<E> implements Iterator<E> {
 
   // TODO(4504458): Replace set_ with set.
   HashSetIterator(HashSetImplementation<E> set_)
@@ skipping 43 matching lines @@
 
 /**
  * A singleton sentinel used to represent when a key is deleted from the map.
  * We can't use [: const Object() :] as a sentinel because it would end up
  * canonicalized and then we cannot distinguish the deleted key from the
  * canonicalized [: Object() :].
  */
 class _DeletedKeySentinel {
   const _DeletedKeySentinel();
 }