Make all blending up to GrOptDrawState be handled by the xp/xp factory.

In this cl the blending information is extracted for the xp and stored in the ODS
which is then used as it currently is. In the follow up cl, an XP backend will be added
and at that point all blending work will take place inside XP's.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/7c66342a399b529634bed0fabfaa562db2c0dbd4

Review URL: https://codereview.chromium.org/759713002
22 files changed