Remove dart:codec and move classes into dart:convert.

tests/lib/convert/utf83_test.dart

 // Copyright (c) 2012, 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_test;
 import "package:expect/expect.dart";
-import 'dart:codec';
 import 'dart:convert';
 
 main() {
   // Test that UTF8-decoder removes leading BOM.
   Expect.equals("a", UTF8.decode([0xEF, 0xBB, 0xBF, 0x61]));
   Expect.equals("a", UTF8.decoder.convert([0xEF, 0xBB, 0xBF, 0x61]));
   Expect.equals("a", new Utf8Decoder().convert([0xEF, 0xBB, 0xBF, 0x61]));
   Expect.equals("a",
                 UTF8.decode([0xEF, 0xBB, 0xBF, 0x61], allowMalformed: true));
   Expect.equals("a", new Utf8Codec(allowMalformed: true)
@@ skipping 19 matching lines @@
                 new Utf8Decoder().convert([0x61, 0xEF, 0xBB, 0xBF]));
   Expect.equals("a\u{FEFF}",
                 UTF8.decode([0x61, 0xEF, 0xBB, 0xBF], allowMalformed: true));
   Expect.equals("a\u{FEFF}", new Utf8Codec(allowMalformed: true)
                          .decode([0x61, 0xEF, 0xBB, 0xBF]));
   Expect.equals("a\u{FEFF}", new Utf8Codec(allowMalformed: true)
                          .decoder.convert([0x61, 0xEF, 0xBB, 0xBF]));
   Expect.equals("a\u{FEFF}", new Utf8Decoder(allowMalformed: true)
                          .convert([0x61, 0xEF, 0xBB, 0xBF]));
 }