Combine unmodifiable_collection package into collection_helpers.

pkg/collection_helpers/lib/wrappers.dart

 // Copyright (c) 2013, 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.
 
 /**
  * Delegating wrappers for [Iterable], [List], [Set], [Queue] and [Map].
+ *
+ * Also adds unmodifiable views for `Set` and `Map`, and a fixed length
+ * view for `List`. The unmodifable list view from `dart:collection` is exported
+ * as well, just for completeness.
  */
-library dart.collection_helper.wrappers;
+library dart.collection_helpers.wrappers;
 
 import "dart:collection";
 import "dart:math" show Random;
 
+export "dart:collection" show UnmodifiableListView;
+
+part "unmodifiable_wrappers.dart";
+
 /**
  * Creates an [Iterable] that delegates all operations to a base iterable.
  *
  * This class can be used hide non-`Iterable` methods of an iterable object,
  * or it can be extended to add extra functionality on top of an existing
  * iterable object.
  */
 class DelegatingIterable<E> implements Iterable<E> {
   Iterable<E> _base;
 
@@ skipping 290 matching lines @@
   Iterable<K> get keys => _base.keys;
 
   int get length => _base.length;
 
   V putIfAbsent(K key, V ifAbsent()) => _base.putIfAbsent(key, ifAbsent);
 
   V remove(Object key) => _base.remove(key);
 
   Iterable<V> get values => _base.values;
 }