Revert[4] "replace SkXfermode obj with SkBlendMode enum in paints"

This reverts commit 2cbcd12281ee807214df094964c584c78932e10b.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2924

Change-Id: I0fa5c58af428f3da8565465d1219a34ef8417d9a
Reviewed-on: https://skia-review.googlesource.com/2924
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
139 files changed