Make XPFragmentBuilder only Builder with access to DstCopy.

src/effects/gradients/SkGradientShader.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGradientShaderPriv.h"
 #include "SkLinearGradient.h"
 #include "SkRadialGradient.h"
@@ skipping 1010 matching lines @@
 
     return key;
 }
 
 void GrGLGradientEffect::emitColor(GrGLFPBuilder* builder,
                                    const GrGradientEffect& ge,
                                    const char* gradientTValue,
                                    const char* outputColor,
                                    const char* inputColor,
                                    const TextureSamplerArray& samplers) {
-    GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
+    GrGLFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
     if (SkGradientShaderBase::kTwo_GpuColorType == ge.getColorType()){
         fsBuilder->codeAppendf("\tvec4 colorTemp = mix(%s, %s, clamp(%s, 0.0, 1.0));\n",
                                builder->getUniformVariable(fColorStartUni).c_str(),
                                builder->getUniformVariable(fColorEndUni).c_str(),
                                gradientTValue);
         // Note that we could skip this step if both colors are known to be opaque. Two
         // considerations:
         // The gradient SkShader reporting opaque is more restrictive than necessary in the two pt
         // case. Make sure the key reflects this optimization (and note that it can use the same
         // shader as thekBeforeIterp case). This same optimization applies to the 3 color case below.
@@ skipping 161 matching lines @@
             (*stops)[i] = stop;
             stop = i < outColors - 1 ? stop + random->nextUScalar1() * (1.f - stop) : 1.f;
         }
     }
     *tm = static_cast<SkShader::TileMode>(random->nextULessThan(SkShader::kTileModeCount));
 
     return outColors;
 }
 
 #endif