pkg/mime: Removed mutable state from MimeMultipartTransformer

pkg/mime/lib/src/char_code.dart

Index: pkg/mime/lib/src/char_code.dart
diff --git a/pkg/mime/lib/src/char_code.dart b/pkg/mime/lib/src/char_code.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f455e681aff9d0bfc50d8fb9ff3e13e5fb198a76
--- /dev/null
+++ b/pkg/mime/lib/src/char_code.dart
@@ -0,0 +1,16 @@
+// Copyright (c) 2014, 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 mime.char_code;
+
+class CharCode {
+  static const int HT = 9;
+  static const int LF = 10;
+  static const int CR = 13;
+  static const int SP = 32;
+  static const int DASH = 45;
+  static const int COLON = 58;
+  static const int UPPER_A = 65;
+  static const int UPPER_Z = 90;
+  static const int LOWER_A = 97;
+}