Import rasta tests.

pkg/fasta/test/rasta/super_initializer.dart

+// Copyright (c) 2016, 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.md file.
+
+class Super {
+  Super.arg0();
+  Super.arg1(a);
+  Super.arg2(a, b);
+}
+
+class Sub extends Super {
+  var field;
+  Sub.arg0() : super.arg0(), field = 42;
+  Sub.arg1(a) : super.arg1(a), field = 42;
+  Sub.arg2(a, b) : super.arg2(a, b), field = 42;
+}