Make all GrFragmentProcessors GL independent.

src/gpu/glsl/GrGLSLBlend.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 GrGLBlend_DEFINED
 #define GrGLBlend_DEFINED
 
 #include "SkXfermode.h"
 
 class GrGLSLFragmentBuilder;
 
 namespace GrGLSLBlend {
     /*
      * Appends GLSL code to fsBuilder that assigns a specified blend of the srcColor and dstColor
      * variables to the outColor variable.
      */
     void AppendMode(GrGLSLFragmentBuilder* fsBuilder, const char* srcColor,
                     const char* dstColor, const char* outColor, SkXfermode::Mode mode);
 };
 
 #endif