Unify list.

corelib/src/implementation/list.dart

+// Copyright (c) 2011, 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.
+
+/**
+ * A [List] is an indexable collection with a length. It can be of
+ * fixed size or extendable.
+ */
+class ListImplementation<E> {
+  /**
+   * Factory implementation of List().
+   *
+   * Creates a list of the given [length].
+   */
+  external factory List([int length]);
+
+  /**
+   * Factory implementation of List.from().
+   *
+   * Creates a list with the elements of [other]. The order in
+   * the list will be the order provided by the iterator of [other].
+   */
+  factory List.from(Iterable<E> other) {
+    // TODO(ajohnsen): Make external once the vm can handle it, so we don't
+    // lose generic type information.
+    // Issue: #4727
+    return _from(other);
+  }
+
+  external static _from(Iterable<E> other);
+}