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

frog/tests/leg_only/basic_class_test.dart

-// Copyright (c) 2011, 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 {
-}
-
-class SubA extends A {
-}
-
-class B {
-}
-
-void main() {
-  A a;
-  SubA subA;
-  B b;
-  a = a;
-  a = subA;
-  a = b; /// 01: static type warning
-  subA = a;
-  subA = subA;
-  subA = b; /// 02: static type warning
-  b = a; /// 03: static type warning
-  b = subA; /// 04: static type warning
-  b = b;
-}