Move kernel baseline tests to front_end.

pkg/kernel/testcases/input/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']);
-}