Make sure we throw the right NSM error when indexing out of range of a variable that can be null.

tests/language/inference_list_or_null_test.dart

+// 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.
+
+// Regression test for dart2js that used to statically inline the length of an
+// array held in a variable when it could, even if that variable could
+// be null.
+
+import "package:expect/expect.dart";
+
+var list;
+
+main() {
+  if (new DateTime.now().millisecondsSinceEpoch == 0) list = new List(4);
+  Expect.throws(() => print(list[5]), (e) => e is NoSuchMethodError);
+}