Move kernel baseline tests to front_end.

pkg/front_end/testcases/classes.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 file.
 
 class A {
   final int x;
   final int y;
   A(this.y) : x = 42;
   method() {
     print("A.method x: $x y: $y");
     print(this);
     print(this.runtimeType);
   }
 }
 
 class B extends A {
   B(x) : super(x);
   method() {
     print("B.method x: $x y: $y");
     super.method();
   }
 }
 
 main() {
   A a = new A(87);
   B b = new B(117);
   a.method();
   b.method();
 }