Fix nullaware dynamic dispatch

tests/language_strong/nullaware_dynamic_test.dart

Index: tests/language_strong/nullaware_dynamic_test.dart
diff --git a/tests/language_strong/nullaware_dynamic_test.dart b/tests/language_strong/nullaware_dynamic_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..36dfc10f6d71da909607e95631b8bbc7090450f2
--- /dev/null
+++ b/tests/language_strong/nullaware_dynamic_test.dart
@@ -0,0 +1,17 @@
+// Copyright (c) 2017, 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';
+
+void main() {
+  dynamic l;
+  var val = l?.first?.abs();
+  Expect.equals(null, val);
+  l = [null, -2, -3];
+  val = l?.first?.abs();
+  Expect.equals(null, val);
+  l = [-1, -2, -3];
+  val = l?.first?.abs();
+  Expect.equals(1, val);
+}