Language tests updated to use const instead of final.

tests/language/library12.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.
 //
 
 #library("library12.dart");
 
 #import("library11.dart");
 class Library12 {
   Library12(this.fld);
@@ skipping 19 matching lines @@
     Expect.equals(200, top_level_func11());
     return 3;
   }
   static var static_fld = 4;
 }
 
 interface Library12Interface {
   Library12 addObjects(Library12 value1, Library12 value2);
 }
 
-final int top_level12 = 10;
+const int top_level12 = 10;
 top_level_func12() {
   return 20;
 }