Move kernel baseline tests to front_end.

pkg/front_end/testcases/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');
 }