Implement SkBlender support in Ganesh.

SkBlenderBase::asFragmentProcessor now returns a working runtime-blender
FP. This FP is appended to the end of the paintFP chain by
skpaint_to_grpaint_impl when an SkPaint contains an SkBlender, and the
GrPaint's XferProcessor factory is set to kSrc.

Unit tests have been added to verify basic functionality is working as
expected; more thorough drawing tests will be added once the CPU side is
running as well (since we don't want GMs that render differently on CPU
and GPU).

Change-Id: I255abd057fa75d638a9f2612c1a353be4de9e24c
Bug: skia:12080
Reviewed-by: Brian Osman <>
Commit-Queue: Brian Osman <>
Commit-Queue: John Stiles <>
Auto-Submit: John Stiles <>
8 files changed