Add List.asMap().

sdk/lib/core/list.dart

 // 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.
 
 part of dart.core;
 
 /**
  * A [List] is an indexable collection with a length.
  *
  * A `List` implementation can be choose not to support all methods
@@ skipping 239 matching lines @@
    * Throws an [UnsupportedError] if the list is
    * not extendable.
    * If [length] is 0, this method does not do anything.
    * If [start] is the length of the list, this method inserts the
    * range at the end of the list.
    * Throws an [ArgumentError] if [length] is negative.
    * Throws an [RangeError] if [start] is negative or if
    * [start] is greater than the length of the list.
    */
   void insertRange(int start, int length, [E fill]);
+
+  /**
+   * Returns an unmodifiable [Map] view of `this`.
+   *
+   * It has the indices of this list as keys, and the corresponding elements
+   * as values.
+   */
+  Map<int, E> asMap();
 }