Added tree structure to GrGLFragmentProcessor, i.e. GL instances

src/effects/SkArithmeticMode_gpu.h

Index: src/effects/SkArithmeticMode_gpu.h
diff --git a/src/effects/SkArithmeticMode_gpu.h b/src/effects/SkArithmeticMode_gpu.h
index 36f0f4002474928b54d5953a3b7a73afcec84545..4f780cf71b6d73e614a550641ee4419010f30d95 100644
--- a/src/effects/SkArithmeticMode_gpu.h
+++ b/src/effects/SkArithmeticMode_gpu.h
@@ -42,8 +42,6 @@ public:
 
     const char* name() const override { return "Arithmetic"; }
 
-    GrGLFragmentProcessor* createGLInstance() const override;
-
     float k1() const { return fK1; }
     float k2() const { return fK2; }
     float k3() const { return fK3; }
@@ -51,6 +49,8 @@ public:
     bool enforcePMColor() const { return fEnforcePMColor; }
 
 private:
+    GrGLFragmentProcessor* onCreateGLInstance() const override;
+
     void onGetGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;
 
     bool onIsEqual(const GrFragmentProcessor&) const override;