Make XPFragmentBuilder only Builder with access to DstCopy.

src/effects/SkAlphaThresholdFilter.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkAlphaThresholdFilter.h"
 #include "SkBitmap.h"
 #include "SkReadBuffer.h"
@@ skipping 136 matching lines @@
                                         const TextureSamplerArray& samplers) {
     fInnerThresholdVar = builder->addUniform(
         GrGLProgramBuilder::kFragment_Visibility,
         kFloat_GrSLType, kDefault_GrSLPrecision,
         "inner_threshold");
     fOuterThresholdVar = builder->addUniform(
         GrGLProgramBuilder::kFragment_Visibility,
         kFloat_GrSLType, kDefault_GrSLPrecision,
         "outer_threshold");
 
-    GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
+    GrGLFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
     SkString coords2D = fsBuilder->ensureFSCoords2D(coords, 0);
     SkString maskCoords2D = fsBuilder->ensureFSCoords2D(coords, 1);
 
     fsBuilder->codeAppendf("\t\tvec2 coord = %s;\n", coords2D.c_str());
     fsBuilder->codeAppendf("\t\tvec2 mask_coord = %s;\n", maskCoords2D.c_str());
     fsBuilder->codeAppend("\t\tvec4 input_color = ");
     fsBuilder->appendTextureLookup(samplers[0], "coord");
     fsBuilder->codeAppend(";\n");
     fsBuilder->codeAppend("\t\tvec4 mask_color = ");
     fsBuilder->appendTextureLookup(samplers[1], "mask_coord");
@@ skipping 209 matching lines @@
 }
 
 #ifndef SK_IGNORE_TO_STRING
 void SkAlphaThresholdFilterImpl::toString(SkString* str) const {
     str->appendf("SkAlphaThresholdImageFilter: (");
     str->appendf("inner: %f outer: %f", fInnerThreshold, fOuterThreshold);
     str->append(")");
 }
 #endif