Add StringScanner.substring.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//701723002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/string_scanner@41536 260f80e4-7a28-3924-810f-c04153c831b5
4 files changed
tree: 3db358ae4191bcb587ae0512548d1b9b59052705
  1. pkgs/