Revert[7] "replace SkXfermode obj with SkBlendMode enum in paints"

Revert[7] "replace SkXfermode obj with SkBlendMode enum in paints"

This reverts commit Ib4a154cdd5f5d1dcac921ef50d53b79a2d6a1be8.

Reason for revert: new assert from 100K bot

Original change's description:
> Revert[6] "replace SkXfermode obj with SkBlendMode enum in paints"
>
> - perform version check in CreateProc for XfermodeImageFilter and ArithmeticImageFilter
> This reverts commit 3ed485f4249e17abb4b11f5018d03175fd1afb44.
>
> BUG=skia:
>
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2992
>
> Change-Id: Ib4a154cdd5f5d1dcac921ef50d53b79a2d6a1be8
> Reviewed-on: https://skia-review.googlesource.com/2992
> Reviewed-by: Mike Reed <reed@google.com>
> Commit-Queue: Mike Reed <reed@google.com>
>

TBR=reed@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I848e5a69c5cd67f2c14889f4f0a346652578c4ff
Reviewed-on: https://skia-review.googlesource.com/3023
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>