Revert "Revert "replace SkXfermode obj with SkBlendMode enum in paints""

This reverts commit ce02e7175872abde3721df9e5d3ec0ab8384cd8e.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2878

Change-Id: I86875511a13497112827cbaed1dbd7639e9e3d10
Reviewed-on: https://skia-review.googlesource.com/2878
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Reed <reed@google.com>
139 files changed