Scale picture shader (GPU) by input alpha

Bug: skia:12476, skia:11942
Change-Id: Iee94470e117788f88516af9aaa8950434278f662
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/452559
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
2 files changed