Add a leg_only test suite, and make sure to run it in our presubmit script.

frog/leg/tests/statements.dart

Index: frog/leg/tests/statements.dart
===================================================================
--- frog/leg/tests/statements.dart	(revision 1300)
+++ frog/leg/tests/statements.dart	(working copy)
@@ -1,20 +0,0 @@
-// 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.
-
-void main() {
-  print(3);
-  print(4);
-  /*
-  if (true) {
-    print('hest');
-  }
-  if (false) {
-    print('hest');
-  } else {
-    print('fisk');
-  }
-  int foo() {}
-  int i = 0;
-  */
-}