replace Arithmetic xfermode with imagefilter

replace Arithmetic xfermode with imagefilter

chrome pre-cl: https://codereview.chromium.org/2369023002/

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2595

Change-Id: Ia3f3b721854c516f3b7f8c44f71f40a8a2eeb9b4
Reviewed-on: https://skia-review.googlesource.com/2595
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Robert Phillips <robertphillips@google.com>