Opt for advanced blend at creation time in CrCustomXfermode

src/gpu/effects/GrCustomXfermodePriv.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrCustomXfermodePriv_DEFINED
 #define GrCustomXfermodePriv_DEFINED
 
@@ skipping 67 matching lines @@
                           const GrProcOptInfo& coveragePOI) const override;
 
     bool onIsEqual(const GrXPFactory& xpfBase) const override {
         const GrCustomXPFactory& xpf = xpfBase.cast<GrCustomXPFactory>();
         return fMode == xpf.fMode;
     }
 
     GR_DECLARE_XP_FACTORY_TEST;
 
     SkXfermode::Mode fMode;
+    GrBlendEquation  fHWBlendEquation;
 
     typedef GrXPFactory INHERITED;
 };
 #endif