Add Iterable.fold (and Stream.fold) which replace `reduce`.

For now this is just a copy. In a next step we will change the behavior of
`reduce`.

BUG= http://dartbug.com/9536

Review URL: https://codereview.chromium.org//13548002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/http@20978 260f80e4-7a28-3924-810f-c04153c831b5
1 file changed
tree: 7c21a23ec7c726ea83b4ca7577908dbadee14965
  1. lib/
  2. test/
  3. pubspec.yaml