Create fragment processor for performing input color blend with child processor

include/gpu/effects/GrCustomXfermode.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 GrCustomXfermode_DEFINED
 #define GrCustomXfermode_DEFINED
 
 #include "SkXfermode.h"
 
-class GrFragmentProcessor;
 class GrTexture;
 
 /**
  * Custom Xfer modes are used for blending when the blend mode cannot be represented using blend
- * coefficients. It is assumed that all blending is done within the processors' emit code. For each
- * blend mode there should be a matching fragment processor (used when blending with a background
- * texture) and xfer processor.
+ * coefficients.
  */
 namespace GrCustomXfermode {
-    bool IsSupportedMode(SkXfermode::Mode mode); 
-
-    GrFragmentProcessor* CreateFP(GrProcessorDataManager*, SkXfermode::Mode mode,
-                                  GrTexture* background);
-
+    bool IsSupportedMode(SkXfermode::Mode mode);
     GrXPFactory* CreateXPFactory(SkXfermode::Mode mode);
 };
 
 #endif