Make XPFragmentBuilder only Builder with access to DstCopy.
Plus a bunch of renaming.

BUG=skia:

Review URL: https://codereview.chromium.org/1110033004
diff --git a/src/gpu/effects/GrBezierEffect.cpp b/src/gpu/effects/GrBezierEffect.cpp
index 6eeda90..041cfd7 100644
--- a/src/gpu/effects/GrBezierEffect.cpp
+++ b/src/gpu/effects/GrBezierEffect.cpp
@@ -90,7 +90,7 @@
     this->emitTransforms(pb, gpArgs->fPositionVar, gp.inPosition()->fName, gp.localMatrix(),
                          args.fTransformsIn, args.fTransformsOut);
 
-    GrGLGPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
+    GrGLFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
     fsBuilder->codeAppend("float edgeAlpha;");
 
     switch (fEdgeType) {
@@ -325,7 +325,7 @@
     this->emitTransforms(pb, gpArgs->fPositionVar, gp.inPosition()->fName, gp.localMatrix(),
                          args.fTransformsIn, args.fTransformsOut);
 
-    GrGLGPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
+    GrGLFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
     fsBuilder->codeAppendf("float edgeAlpha;");
 
     switch (fEdgeType) {
@@ -539,7 +539,7 @@
     this->emitTransforms(args.fPB, gpArgs->fPositionVar, gp.inPosition()->fName, gp.localMatrix(),
                          args.fTransformsIn, args.fTransformsOut);
 
-    GrGLGPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
+    GrGLFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
 
     GrGLShaderVar edgeAlpha("edgeAlpha", kFloat_GrSLType, 0, kHigh_GrSLPrecision);
     GrGLShaderVar dklmdx("dklmdx", kVec3f_GrSLType, 0, kHigh_GrSLPrecision);