Add more specialized fragment builders

src/effects/SkDisplacementMapEffect.cpp

Index: src/effects/SkDisplacementMapEffect.cpp
diff --git a/src/effects/SkDisplacementMapEffect.cpp b/src/effects/SkDisplacementMapEffect.cpp
index 5aef212f3dfdfe6b25f2b3b5b4dd418a478633d6..7940203bddba0fd9aa6a02f71b5f0358ada322c4 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -553,7 +553,7 @@ void GrGLDisplacementMapEffect::emitCode(EmitArgs& args) {
                                    // a number smaller than that to approximate 0, but
                                    // leave room for 32-bit float GPU rounding errors.
 
-    GrGLSLFragmentBuilder* fragBuilder = args.fFragBuilder;
+    GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
     fragBuilder->codeAppendf("\t\tvec4 %s = ", dColor);
     fragBuilder->appendTextureLookup(args.fSamplers[0], args.fCoords[0].c_str(),
                                    args.fCoords[0].getType());