Revert "replace Arithmetic xfermode with imagefilter"

This reverts commit Ia3f3b721854c516f3b7f8c44f71f40a8a2eeb9b4.

Reason for revert: need to guard the no-gpu codepath

Original issue's description:
> 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>
> 

TBR=robertphillips@google.com,fmalita@chromium.org,fmalita@google.com,reed@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I761799b594a0379c6bf356e6abc73552c3d19480
Reviewed-on: https://skia-review.googlesource.com/2661
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
12 files changed