pkg/crypto: tighten up

Added return types, marked fields as final

R=floitsch@google.com

Review URL: https://codereview.chromium.org//23619068

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/crypto@27606 260f80e4-7a28-3924-810f-c04153c831b5
4 files changed
tree: 60b39be0155e73808dbdda86950363b6190d0f71
  1. lib/
  2. test/
  3. pubspec.yaml