Use Skia drawing when doing conversion operations that may need dither

Skia plans to remove the automatic dithering during readPixels/writePixels.
This change retains dithering (and thus image quality) on low-end devices.

Bug: chromium:720105 skia:8787
Change-Id: I8c593f0f72953bcfbed5b5107db262beb4a60ad4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1495208
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637316}
2 files changed