Use views throughout gpu blur code.

Bug: skia:9556
Change-Id: I3988c8112d72d5453cf93e58542eb68b16e67e1c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/267452
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
13 files changed