Look up the correct constructor for default classes.

lib/compiler/implementation/lib/mockimpl.dart

Index: lib/compiler/implementation/lib/mockimpl.dart
diff --git a/lib/compiler/implementation/lib/mockimpl.dart b/lib/compiler/implementation/lib/mockimpl.dart
index 0182b37e4675734d5df3975e52ae3940966ea48f..d6d8f5dc353dcc23da8a134c4f1f59022f97c6de 100644
--- a/lib/compiler/implementation/lib/mockimpl.dart
+++ b/lib/compiler/implementation/lib/mockimpl.dart
@@ -388,7 +388,7 @@ class DateImplementation implements Date {
   var _asJs() => Primitives.lazyAsJsDate(this);
 }
 
-class ListFactory<E> implements List<E> {
+class ListFactory<E> {
   factory List([int length]) => Primitives.newList(length);
   factory List.from(Iterable<E> other) {
     List<E> result = new List<E>();