Move kernel baseline tests to front_end.

pkg/front_end/testcases/store_load.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 Foo {
   var _field;
 }
 
 class FooValue {}
 
 class Bar {
   var _field; // Same name.
 }
 
 class BarValue {}
 
 main() {
   var foo = new Foo();
   foo._field = new FooValue();
   var fooValue = foo._field;
   print(fooValue);
 
   var bar = new Bar();
   bar._field = new BarValue();
   var barValue = bar._field;
   print(barValue);
 }