Also deal with List.filled in the backend, not just the inferrer and list tracer.

tests/corelib/list_filled_type_argument_test.dart

Index: tests/corelib/list_filled_type_argument_test.dart
===================================================================
--- tests/corelib/list_filled_type_argument_test.dart	(revision 0)
+++ tests/corelib/list_filled_type_argument_test.dart	(revision 0)
@@ -0,0 +1,11 @@
+// Copyright (c) 2013, 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.
+
+import "package:expect/expect.dart";
+
+main() {
+  var a = new List<int>.filled(42, 42);
+  Expect.isTrue(a is List<int>);
+  Expect.isFalse(a is List<String>);
+}