Add transformer support to Converters.

tests/lib/convert/unicode_tests.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 utf8_tests;
+library unicode_tests;
 
 // Google favorite: "Îñţérñåţîöñåļîžåţîờñ".
 const INTER_BYTES = const [0xc3, 0x8e, 0xc3, 0xb1, 0xc5, 0xa3, 0xc3, 0xa9, 0x72,
                            0xc3, 0xb1, 0xc3, 0xa5, 0xc5, 0xa3, 0xc3, 0xae, 0xc3,
                            0xb6, 0xc3, 0xb1, 0xc3, 0xa5, 0xc4, 0xbc, 0xc3, 0xae,
                            0xc5, 0xbe, 0xc3, 0xa5, 0xc5, 0xa3, 0xc3, 0xae, 0xe1,
                            0xbb, 0x9d, 0xc3, 0xb1];
 const INTER_STRING = "Îñţérñåţîöñåļîžåţîờñ";
 
 // Blueberry porridge in Danish: "blåbærgrød".
@@ skipping 51 matching lines @@
     for (int i = 0; i < 100; i++) {
       longBytes.addAll(bytes);
       longString += string;
     }
     return [test, [longBytes, longString]];
   }));
   return tests;
 }
 
 final List UNICODE_TESTS = _expandTestPairs();