add an api usage example (dart-lang/source_span#92)

* add an api usage example

* Apply suggestions from code review

Co-authored-by: Kevin Moore <kevmoo@users.noreply.github.com>

* make method private

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Co-authored-by: Kevin Moore <kevmoo@users.noreply.github.com>
4 files changed
tree: a97920641c2df354b4938ddaa572ef4a39b36cf0
  1. pkgs/