Move generated files to gen/.

test/codegen/syncstar_syntax.dart

-// Copyright (c) 2015, 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.
-
-import 'package:expect/expect.dart';
-
-Iterable<int> foo() sync* {
-  yield 1;
-  yield* [2, 3];
-}
-
-class Class {
-  Iterable<int> bar() sync* {
-    yield 1;
-    yield* [2, 3];
-  }
-
-  static Iterable<int> baz() sync* {
-    yield 1;
-    yield* [2, 3];
-  }
-}
-
-main() {
-  Iterable<int> qux() sync* {
-    yield 1;
-    yield* [2, 3];
-  }
-
-  Expect.listEquals([1, 2, 3], foo().toList());
-  Expect.listEquals([1, 2, 3], new Class().bar().toList());
-  Expect.listEquals([1, 2, 3], Class.baz().toList());
-  Expect.listEquals([1, 2, 3], qux().toList());
-}