Update Dawn backend to accommodate recent Skia API changes.

Change-Id: Ib0667fbff9a16fe796378134a17008ece6267d06
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/240508
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>
4 files changed