Fix compilation of Dawn backend after GrMesh/GrPrimitiveType change

Change-Id: Ia37863dacffacd344086fa513baa9c274443554c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271836
Commit-Queue: Stephen White <senorblanco@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>
2 files changed