Improve List implementation.

dart/frog/leg/lib/mockimpl.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 classes and interfaces that Leg cannot read directly.
 
 // TODO(ahe): Remove this file.
 
 class JSSyntaxRegExp implements RegExp {
   JSSyntaxRegExp(String pattern,
@@ skipping 466 matching lines @@
     } else {
       equivalentYear = years;
       offsetInSeconds = 0;
     }
     int secondsSinceEpoch = Primitives.brokenDownDateToSecondsSinceEpoch(
         equivalentYear, month, day, hours, minutes, seconds, isUtc);
     int adjustedSeconds = secondsSinceEpoch + offsetInSeconds;
     return adjustedSeconds * Duration.MILLISECONDS_PER_SECOND + milliseconds;
   }
 }
+
+class ListFactory<E> implements List<E> {
+  factory List([int length]) => Primitives.newList(length);
+  factory List.from(Iterable<E> other) {
+    List<E> result = new List<E>();
+    // TODO(ahe): Use for-in when it is implemented correctly.
+    Iterator<E> iterator = other.iterator();
+    while (iterator.hasNext()) {
+      result.add(iterator.next());
+    }
+    return result;
+  }
+}