Remove deprecated string features.

sdk/lib/_collection_dev/list.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.
 
 part of dart._collection.dev;
 
 /**
  * Class implementing the read-operations on [List].
  *
  * Implements all read-only operations, except [:operator[]:] and [:length:],
@@ skipping 283 matching lines @@
 }
 
 class ReversedListIterable<E> extends ListIterable<E> {
   Iterable<E> _source;
   ReversedListIterable(this._source);
 
   int get length => _source.length;
 
   E elementAt(int index) => _source.elementAt(_source.length - 1 - index);
 }
+
+/**
+ * An [Iterable] of the UTF-16 code units of a [String] in index order.
+ */
+class CodeUnits extends UnmodifiableListBase<int> {
+  /** The string that this is the code units of. */
+  String _string;
+
+  CodeUnits(this._string);
+
+  int get length => _string.length;
+  int operator[](int i) => _string.codeUnitAt(i);
+}