Move kernel baseline tests to front_end.

pkg/front_end/testcases/arithmetic.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.
 int foo(int x, int y) {
   var z = x + y;
   return z << 4;
 }
 
 void loop(List xs) {
   int _ = xs.length;
   for (int i = 0; i < xs.length; i++) {}
 }
 
 main() {
   foo(4, 5);
   foo(6, 7);
   loop(['dfg']);
 }