Fix cloning of Runtime Blend fragment processors.

Previously, a cloned Runtime Blend FP would lose its
kIsBlendFunction_Flag, causing invalid code to be generated.

This broke the `filltypespersp` slide when "Force Runtime Blends" is on.

Change-Id: I9a140bc6467536e5ebeb2ca47eca6f013462dd58
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/434919
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed