By comparing the old substring to the new full body, we can do a pretty
good job at creating a new substring.
This is not an exact science. Always carefully examine the newly
generated strings for correctness.
Change-Id: I8bdf591539a32ec42d0444aa054d88a933e4d250
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/47765
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Ben Clayton