Modify the Report representation to be a list of Change values,
instead of two string slices.
This will enable adding more information to each change, like source
location.
Change-Id: Ia7389d7bc552479ea5e06efd7fdefe004058e66f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/172777
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>