Dawn: implement Sampler cache (optimization).

Change-Id: I0b1fabadb3fddd90350eff3b13037ce92c5dbfd8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/238178
Commit-Queue: Stephen White <senorblanco@chromium.org>
Reviewed-by: Greg Daniel <egdaniel@google.com>
4 files changed