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/GrBitmapTextGeoProc.cpp b/src/gpu/effects/GrBitmapTextGeoProc.cpp
index 9834a76..fab7ec2 100644
--- a/src/gpu/effects/GrBitmapTextGeoProc.cpp
+++ b/src/gpu/effects/GrBitmapTextGeoProc.cpp
@@ -60,7 +60,7 @@
         this->emitTransforms(args.fPB, gpArgs->fPositionVar, cte.inPosition()->fName,
                              cte.localMatrix(), args.fTransformsIn, args.fTransformsOut);
 
-        GrGLGPFragmentBuilder* fsBuilder = pb->getFragmentShaderBuilder();
+        GrGLFragmentBuilder* fsBuilder = pb->getFragmentShaderBuilder();
         if (cte.maskFormat() == kARGB_GrMaskFormat) {
             fsBuilder->codeAppendf("%s = ", args.fOutputColor);
             fsBuilder->appendTextureLookupAndModulate(args.fOutputColor,