Partially defer GrSWMaskHelper

This is intended to position the writePixels in GrSWMaskHelper::toTexture for moving to GrSurfaceContext

Change-Id: I6c3d24eb3b1db3b0efc63f7f4f1240a7a00ee88a
Reviewed-on: https://skia-review.googlesource.com/6032
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index 4df4461..b8306f3 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -186,6 +186,7 @@
   "$_src/gpu/GrStencilSettings.h",
   "$_src/gpu/GrStyle.cpp",
   "$_src/gpu/GrStyle.h",
+  "$_src/gpu/GrSurfaceContextPriv.h",
   "$_src/gpu/GrTessellator.cpp",
   "$_src/gpu/GrTessellator.h",
   "$_src/gpu/GrTextureOpList.cpp",