Make List an abstract class.

runtime/lib/array_patch.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.
 
 // Note that the optimizing compiler depends on the algorithm which
 // returns a _GrowableObjectArray if length is null, otherwise returns
 // fixed size array.
-patch class _ListImpl<E> {
+patch class List<E> {
   /* patch */ factory List([int length = null]) {
     if (length == null) {
       return new _GrowableObjectArray<E>();
     } else {
       return new _ObjectArray<E>(length);
     }
   }
 
-  /* patch */ factory List.from(Iterable<E> other) {
-    _GrowableObjectArray<E> list = new _GrowableObjectArray<E>();
-    for (final e in other) {
-      list.add(e);
-    }
-    return list;
-  }
-
   // Factory constructing a mutable List from a parser generated List literal.
   // [elements] contains elements that are already type checked.
   factory List._fromLiteral(List elements) {
     var list = new List<E>();
     if (elements.length > 0) {
       list._setData(elements);
       list.length = elements.length;
     }
     return list;
   }
 }