Make XPFragmentBuilder only Builder with access to DstCopy.

src/gpu/effects/GrDitherEffect.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDitherEffect.h"
 #include "GrFragmentProcessor.h"
 #include "GrInvariantOutput.h"
@@ skipping 69 matching lines @@
 
 GLDitherEffect::GLDitherEffect(const GrProcessor&) {
 }
 
 void GLDitherEffect::emitCode(GrGLFPBuilder* builder,
                               const GrFragmentProcessor& fp,
                               const char* outputColor,
                               const char* inputColor,
                               const TransformedCoordsArray&,
                               const TextureSamplerArray& samplers) {
-    GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
+    GrGLFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
     // Generate a random number based on the fragment position. For this
     // random number generator, we use the "GLSL rand" function
     // that seems to be floating around on the internet. It works under
     // the assumption that sin(<big number>) oscillates with high frequency
     // and sampling it will generate "randomness". Since we're using this
     // for rendering and not cryptography it should be OK.
 
     // For each channel c, add the random offset to the pixel to either bump
     // it up or let it remain constant during quantization.
     fsBuilder->codeAppendf("\t\tfloat r = "
                            "fract(sin(dot(%s.xy ,vec2(12.9898,78.233))) * 43758.5453);\n",
                            fsBuilder->fragmentPosition());
     fsBuilder->codeAppendf("\t\t%s = (1.0/255.0) * vec4(r, r, r, r) + %s;\n",
                            outputColor, GrGLSLExpr4(inputColor).c_str());
 }
 
 //////////////////////////////////////////////////////////////////////////////
 
 void DitherEffect::getGLProcessorKey(const GrGLSLCaps& caps,
                                      GrProcessorKeyBuilder* b) const {
     GLDitherEffect::GenKey(*this, caps, b);
 }
 
 GrGLFragmentProcessor* DitherEffect::createGLInstance() const  {
     return SkNEW_ARGS(GLDitherEffect, (*this));
 }
 
 GrFragmentProcessor* GrDitherEffect::Create() { return DitherEffect::Create(); }