Make XPFragmentBuilder only Builder with access to DstCopy.

src/gpu/effects/GrTextureDomain.cpp

Index: src/gpu/effects/GrTextureDomain.cpp
diff --git a/src/gpu/effects/GrTextureDomain.cpp b/src/gpu/effects/GrTextureDomain.cpp
index 3c4f348283d6bd0ad69093324e087c4c888082c4..bd189868e75e477864c7a48e693278cd9f6848d3 100644
--- a/src/gpu/effects/GrTextureDomain.cpp
+++ b/src/gpu/effects/GrTextureDomain.cpp
@@ -197,7 +197,7 @@ void GrGLTextureDomainEffect::emitCode(GrGLFPBuilder* builder,
     const GrTextureDomainEffect& textureDomainEffect = fp.cast<GrTextureDomainEffect>();
     const GrTextureDomain& domain = textureDomainEffect.textureDomain();
 
-    GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
+    GrGLFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
     SkString coords2D = fsBuilder->ensureFSCoords2D(coords, 0);
     fGLDomain.sampleTexture(fsBuilder, domain, outputColor, coords2D, samplers[0], inputColor);
 }