Move kernel baseline tests to front_end.

pkg/front_end/test/fasta/rasta/cascades.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 A {
-  add(x) => x;
-}
-
-main() {
-  var a = new A();
-  f(x) => x;
-  a..add(f)('WHAT');
-}