Improve List implementation.

dart/frog/leg/lib/mock.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.
 
 // Mocks of things that Leg cannot read directly.
 
 // TODO(ahe): Remove this file.
 
 class AssertionError {}
 class TypeError extends AssertionError {}
 class FallThroughError {}
 
 // TODO(ahe): VM specfic exception?
 class InternalError {
   const InternalError(this._msg);
   String toString() => "InternalError: '${_msg}'";
   final String _msg;
 }
 
 // TODO(ahe): VM specfic exception?
 class StaticResolutionException implements Exception {}
 
-class List<E> implements Iterable<E> {
-  factory List([int length]) => Primitives.newList(length);
-  factory List.from(Iterable<E> other) {
-    throw 'List.from is not implemented';
-  }
-}
-
 void assert(condition) {}