Add new SpanScanner.eager().

This is more efficient for uses like the YAML parser, which uses the
current line and especially column information frequently while parsing
a file.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1318603008 .
6 files changed
tree: 9df54391048956daac1542e5088e00eb42ba0ae9
  1. pkgs/