This CL adds the sketch of how to walk the IR tree in order to rebuild
the format of the original control flow.
Bug: tint:1718
Change-Id: Id9376d51907ea2a60f32506a152928b3a82d14ed
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/110481
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>