Language tests updated to use const instead of final.

tests/language/string_interpolation1_negative_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.
 
 // A dollar must be followed by a "{" or an identifier.
 
 class A {
   final String str;
   const A(this.str);
 }
 
 class StringInterpolation1NegativeTest {
   // Dollar not followed by "{" or identifier.
-  static final DOLLAR = const A("$");
+  static const DOLLAR = const A("$");
   testMain() {
   }
 }
 
 main() {
   StringInterpolation1NegativeTest.testMain();
 }