Fix casting bug in GrArithmeticXP

src/effects/SkArithmeticMode_gpu.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkArithmeticMode_gpu.h"
 
 #if SK_SUPPORT_GPU
@@ skipping 195 matching lines @@
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 GrArithmeticXP::GrArithmeticXP(float k1, float k2, float k3, float k4, bool enforcePMColor)
     : fK1(k1)
     , fK2(k2)
     , fK3(k3)
     , fK4(k4)
     , fEnforcePMColor(enforcePMColor) {
-    this->initClassID<GrPorterDuffXferProcessor>();
+    this->initClassID<GrArithmeticXP>();
     this->setWillReadDstColor();
 }
 
 void GrArithmeticXP::getGLProcessorKey(const GrGLCaps& caps, GrProcessorKeyBuilder* b) const {
     GLArithmeticXP::GenKey(*this, caps, b);
 }
 
 GrGLXferProcessor* GrArithmeticXP::createGLInstance() const {
     return SkNEW_ARGS(GLArithmeticXP, (*this));
 }
@@ skipping 34 matching lines @@
     float k1 = random->nextF();
     float k2 = random->nextF();
     float k3 = random->nextF();
     float k4 = random->nextF();
     bool enforcePMColor = random->nextBool();
 
     return GrArithmeticXPFactory::Create(k1, k2, k3, k4, enforcePMColor);
 }
 
 #endif