Check for non-final field in the face of const constructors.

tests/compiler/dart2js/message_kind_helper.dart

 // Copyright (c) 2013, 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 dart2js.test.message_kind_helper;
 
 import 'package:expect/expect.dart';
 import 'dart:async';
 
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart' show
@@ skipping 26 matching lines @@
     return compiler.run(Uri.parse('memory:main.dart')).then((_) {
 
       Expect.isFalse(messages.isEmpty, 'No messages in """$example"""');
 
       String expectedText = !kind.hasHowToFix
           ? kind.template : '${kind.template}\n${kind.howToFix}';
       String pattern = expectedText.replaceAllMapped(
           new RegExp(ESCAPE_REGEXP), (m) => '\\${m[0]}');
       pattern = pattern.replaceAll(new RegExp(r'#\\\{[^}]*\\\}'), '.*');
 
+      // TODO(johnniwinther): Extend MessageKind to contain information on
+      // where info messages are expected.
+      bool messageFound = false;
       for (String message in messages) {
-        Expect.isTrue(new RegExp('^$pattern\$').hasMatch(message),
-                      '"$pattern" does not match "$message"');
+        if (new RegExp('^$pattern\$').hasMatch(message)) {
+          messageFound = true;
+        }
       }
+      Expect.isTrue(messageFound, '"$pattern" does not match any in $messages');
       return compiler;
     });
   }
 
-  return cachedCompiler;
+  return new Future<Compiler>.sync(cachedCompiler);
 }