This CL adds a test for the binding decoration to_str method. Bug: tint:11 Change-Id: Id9d16bdb68c4b68fb8bd67dae898f8b7a17ee6c9 Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/16468 Reviewed-by: Sarah Mashayekhi <sarahmashay@google.com>