Rewrite the const constructor negative tests into a single multi test.

tests/language/src/ConstConstructorNegativeTest.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.
-// Check that class with const constructor has only final fields.
-
-
-class NixFinal {
-  const NixFinal(var v): finalField = v;  // Expect compile error here.
-  final finalField;
-  var nixFinalField;
-}
-
-
-class ConstConstructorNegativeTest {
-  static testMain() {
-    var o = const NixFinal(5);
-    Expect.equals(true, false);
-  }
-}
-
-main() {
-  ConstConstructorNegativeTest.testMain();
-}