Change new List(n) to return fixed length list.

sdk/lib/async/future_impl.dart

Index: sdk/lib/async/future_impl.dart
diff --git a/sdk/lib/async/future_impl.dart b/sdk/lib/async/future_impl.dart
index 85d73af9fa37a6476ea871bef81c4e036527e44d..c36ba4637bd3d14f4b22bf766cc96e9245028c55 100644
--- a/sdk/lib/async/future_impl.dart
+++ b/sdk/lib/async/future_impl.dart
@@ -139,7 +139,7 @@ class _FutureImpl<T> implements Future<T> {
     if (remaining == 0) {
       return new Future.immediate(const []);
     }
-    values = new List.fixedLength(remaining);
+    values = new List(remaining);
     completer = new Completer<List>();
     return completer.future;
   }