Revert of Make specialized SrcOver XPFactory

src/effects/SkArithmeticMode.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkArithmeticMode.h"
 #include "SkColorPriv.h"
 #include "SkReadBuffer.h"
@@ skipping 16 matching lines @@
     virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
                         const SkAlpha aa[]) const override;
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkArithmeticMode_scalar)
 
 #if SK_SUPPORT_GPU
     bool asFragmentProcessor(const GrFragmentProcessor**,
                              const GrFragmentProcessor* dst) const override;
 
-    bool asXPFactory(const GrXPFactory**) const override;
+    bool asXPFactory(GrXPFactory**) const override;
 #endif
 
 private:
     SkArithmeticMode_scalar(SkScalar k1, SkScalar k2, SkScalar k3, SkScalar k4, bool enforcePMColor) {
         fK[0] = k1;
         fK[1] = k2;
         fK[2] = k3;
         fK[3] = k4;
         fEnforcePMColor = enforcePMColor;
     }
@@ skipping 193 matching lines @@
         *fp = GrArithmeticFP::Create(SkScalarToFloat(fK[0]),
                                      SkScalarToFloat(fK[1]),
                                      SkScalarToFloat(fK[2]),
                                      SkScalarToFloat(fK[3]),
                                      fEnforcePMColor,
                                      dst);
     }
     return true;
 }
 
-bool SkArithmeticMode_scalar::asXPFactory(const GrXPFactory** xpf) const {
+bool SkArithmeticMode_scalar::asXPFactory(GrXPFactory** xpf) const {
     if (xpf) {
         *xpf = GrArithmeticXPFactory::Create(SkScalarToFloat(fK[0]),
                                              SkScalarToFloat(fK[1]),
                                              SkScalarToFloat(fK[2]),
                                              SkScalarToFloat(fK[3]),
                                              fEnforcePMColor);
     }
     return true;
 }
 
 #endif
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkArithmeticMode)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkArithmeticMode_scalar)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END