Move frog/tests/{leg,leg_only,frog_native} to tests/compiler/.

frog/tests/leg_only/closure2_test.dart

-// Copyright (c) 2012, 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.
-
-closure0() {
-  // A closure will be implemented as a class. Make sure everything is set up
-  // correctly when no other class is generated. In particular we need
-  // the Dart-Object class to be generated.
-  var f = fun() => 42;
-  Expect.equals(42, f());
-}
-
-main() {
-  closure0();
-}