Add XferProcessor factory in GrPaint and GrDrawState.

src/gpu/gl/GrGLProcessor.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 GrGLProcessor_DEFINED
 #define GrGLProcessor_DEFINED
 
@@ skipping 107 matching lines @@
                           const GrFragmentProcessor& effect,
                           const char* outputColor,
                           const char* inputColor,
                           const TransformedCoordsArray& coords,
                           const TextureSamplerArray& samplers) = 0;
 
 private:
     typedef GrGLProcessor INHERITED;
 };
 
+class GrGLXferProcessor : public GrGLFragmentProcessor {
+public:
+    GrGLXferProcessor(const GrBackendProcessorFactory& factory)
+        : INHERITED(factory) {
+    }
+    
+    virtual ~GrGLXferProcessor() {}
+
+private:
+    typedef GrGLFragmentProcessor INHERITED;
+};
+
 #endif