Language tests updated to use const instead of final.

tests/language/ct_const3_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.
-// Check that initializers of final fields can be declared out of order.
+// Check that initializers of const fields can be declared out of order.
 
-final P = 2 * (O - N);
-final N = 1;
-final O = 1 + 3;
+const P = 2 * (O - N);
+const N = 1;
+const O = 1 + 3;
 
 int main() {
   Expect.equals(1, N);
   Expect.equals(4, O);
   Expect.equals(6, P);
 }