Create associated packages for the dart:collection and dart:async libs.

pkg/collection/lib/src/unmodifiable_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.
 
 /**
  * Wrappers that prevent a List, Set, or Map object from being modified.
  *
  * The [Set] and [Map] wrappers allow reading from the wrapped collection,
  * but prohibit writing.
  *
  * The [List] wrapper prevents changes to the length of the wrapped list,
  * but allows changes to the contents.
  */
-part of dart.collection_helpers.wrappers;
+part of dart.pkg.collection.wrappers;
 
 /**
  * A fixed-length list.
  *
  * A `NonGrowableListView` contains a [List] object and ensures that
  * its length does not change.
  * Methods that would change the length of the list,
  * such as [add] and [remove], throw an [UnsupportedError].
  * All other methods work directly on the underlying list.
  *
@@ skipping 217 matching lines @@
    * operations that change the map are disallowed.
    */
   V remove(K key) { _throw(); }
 
   /**
    * Throws an [UnsupportedError];
    * operations that change the map are disallowed.
    */
   void clear() => _throw();
 }