Use the new "offset" name in span.dart too.

Review URL: https://codereview.chromium.org//397343005

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/source_maps@38376 260f80e4-7a28-3924-810f-c04153c831b5
1 file changed
tree: f3e453611baae268769c522c5d5634d64fc3e951
  1. pkgs/