Add XferProcessor factory in GrPaint and GrDrawState.

include/gpu/GrBackendProcessorFactory.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrBackendProcessorFactory_DEFINED
 #define GrBackendProcessorFactory_DEFINED
 
@@ skipping 122 matching lines @@
         }
         return id;
     }
 
     const uint32_t fProcessorClassID;
     static int32_t fCurrProcessorClassID;
 };
 
 class GrFragmentProcessor;
 class GrGeometryProcessor;
+class GrXferProcessor;
 class GrGLFragmentProcessor;
 class GrGLGeometryProcessor;
+class GrGLXferProcessor;
 
 /**
  * Backend processor factory cannot actually create anything, it is up to subclasses to implement
  * a create binding which matches Gr to GL in a type safe way
  */
 
 class GrBackendFragmentProcessorFactory : public GrBackendProcessorFactory {
 public:
     /**
      * Creates a GrGLProcessor instance that is used both to generate code for the GrProcessor in a
      * GLSL program and to manage updating uniforms for the program when it is used.
      */
     virtual GrGLFragmentProcessor* createGLInstance(const GrFragmentProcessor&) const = 0;
 };
 
+class GrBackendXferProcessorFactory : public GrBackendProcessorFactory {
+public:
+    /**
+     * Creates a GrGLProcessor instance that is used both to generate code for the GrProcessor in a
+     * GLSL program and to manage updating uniforms for the program when it is used.
+     */
+    virtual GrGLXferProcessor* createGLInstance(const GrXferProcessor&) const = 0;
+};
+
 class GrBackendGeometryProcessorFactory : public GrBackendProcessorFactory {
 public:
     /**
      * Creates a GrGLProcessor instance that is used both to generate code for the GrProcessor in a
      * GLSL program and to manage updating uniforms for the program when it is used.
      */
     virtual GrGLGeometryProcessor* createGLInstance(const GrGeometryProcessor&) const = 0;
 };
 
 #endif