Separate SkArithmeticImageFilter from SkXfermodeImageFilter.

Change-Id: I145eed7276456b546ca5c66bc1a0f0f74a84f138
Reviewed-on: https://skia-review.googlesource.com/6728
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/gn/effects.gni b/gn/effects.gni
index 10a2576..30e36b2 100644
--- a/gn/effects.gni
+++ b/gn/effects.gni
@@ -17,9 +17,8 @@
   "$_src/effects/Sk2DPathEffect.cpp",
   "$_src/effects/SkAlphaThresholdFilter.cpp",
   "$_src/effects/SkArcToPathEffect.cpp",
+  "$_src/effects/SkArithmeticImageFilter.cpp",
   "$_src/effects/SkArithmeticMode.cpp",
-  "$_src/effects/SkArithmeticMode_gpu.cpp",
-  "$_src/effects/SkArithmeticMode_gpu.h",
   "$_src/effects/SkBlurDrawLooper.cpp",
   "$_src/effects/SkBlurMask.cpp",
   "$_src/effects/SkBlurMask.h",
@@ -91,6 +90,7 @@
   "$_include/effects/Sk2DPathEffect.h",
   "$_include/effects/SkAlphaThresholdFilter.h",
   "$_include/effects/SkArithmeticMode.h",
+  "$_include/effects/SkArithmeticImageFilter.h",
   "$_include/effects/SkBlurDrawLooper.h",
   "$_include/effects/SkBlurImageFilter.h",
   "$_include/effects/SkBlurMaskFilter.h",