Revert[8] "replace SkXfermode obj with SkBlendMode enum in paints"

src/effects/SkArithmeticModePriv.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkArithmeticModePriv_DEFINED
 #define SkArithmeticModePriv_DEFINED
 
 #include "SkArithmeticMode.h"
 
+struct SkArithmeticParams {
+    float fK[4];
+    bool fEnforcePMColor;
+};
+
 #ifndef SK_SUPPORT_LEGACY_ARITHMETICMODE
 
 class SK_API SkArithmeticMode {
 public:
     /**
      *  result = clamp[k1 * src * dst + k2 * src + k3 * dst + k4]
      *
      *  k1=k2=k3=0, k4=1.0 results in returning opaque white
      *  k1=k3=k4=0, k2=1.0 results in returning the src
      *  k1=k2=k4=0, k3=1.0 results in returning the dst
@@ skipping 10 matching lines @@
 
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP();
 
 private:
     SkArithmeticMode(); // can't be instantiated
 };
 
 #endif
 
 #endif