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/GrDefaultGeoProcFactory.cpp b/src/gpu/GrDefaultGeoProcFactory.cpp
index ae1f4d1..0349af6 100644
--- a/src/gpu/GrDefaultGeoProcFactory.cpp
+++ b/src/gpu/GrDefaultGeoProcFactory.cpp
@@ -86,7 +86,7 @@
             const DefaultGeoProc& gp = args.fGP.cast<DefaultGeoProc>();
             GrGLGPBuilder* pb = args.fPB;
             GrGLVertexBuilder* vsBuilder = pb->getVertexShaderBuilder();
-            GrGLGPFragmentBuilder* fs = args.fPB->getFragmentShaderBuilder();
+            GrGLFragmentBuilder* fs = args.fPB->getFragmentShaderBuilder();
             const BatchTracker& local = args.fBT.cast<BatchTracker>();
 
             // emit attributes