converted Premul / Unpremul to SkSL

Bug: skia:
Change-Id: I4944badbb530e17b9ff7cca389f943e0b5982e01
Reviewed-on: https://skia-review.googlesource.com/72983
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/gn/sksl.gni b/gn/sksl.gni
index 6eec537..3bc0a1d 100644
--- a/gn/sksl.gni
+++ b/gn/sksl.gni
@@ -36,7 +36,9 @@
   "$_src/gpu/effects/GrDitherEffect.fp",
   "$_src/gpu/effects/GrEllipseEffect.fp",
   "$_src/gpu/effects/GrLumaColorFilterEffect.fp",
+  "$_src/gpu/effects/GrPremulInputFragmentProcessor.fp",
   "$_src/gpu/effects/GrRectBlurEffect.fp",
   "$_src/gpu/effects/GrOverdrawFragmentProcessor.fp",
   "$_src/gpu/effects/GrSimpleTextureEffect.fp",
+  "$_src/gpu/effects/GrUnpremulInputFragmentProcessor.fp",
 ]