pkg/mime: Removed mutable state from MimeMultipartTransformer

R=ajohnsen@google.com

Review URL: https://codereview.chromium.org//307963004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/mime@36825 260f80e4-7a28-3924-810f-c04153c831b5
6 files changed
tree: 31fb8620c870a7bdd8630cf29e8e92b140548af4
  1. lib/
  2. test/
  3. LICENSE
  4. pubspec.yaml