converted CircleEffect to SkSL

Bug: skia:
Change-Id: I93d117c22ae2b374294f6a5e961c497ac2c92b09
Reviewed-on: https://skia-review.googlesource.com/23301
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 5ddf18f..c447a7b 100644
--- a/gn/sksl.gni
+++ b/gn/sksl.gni
@@ -26,6 +26,7 @@
 skia_gpu_processor_sources = [
   "$_src/effects/GrAlphaThresholdFragmentProcessor.fp",
   "$_src/effects/GrCircleBlurFragmentProcessor.fp",
+  "$_src/gpu/effects/GrCircleEffect.fp",
   "$_src/gpu/effects/GrDitherEffect.fp",
   "$_src/gpu/effects/GrSimpleTextureEffect.fp",
 ]