Add GrResourceProviderPriv and expose GrGpu in it

Bug: skia:
Change-Id: Iad965ecf33c9dc75c4f068d547698d973f52eb94
Reviewed-on: https://skia-review.googlesource.com/91440
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index f203437..f41dc4a 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -169,6 +169,7 @@
   "$_src/gpu/GrResourceHandle.h",
   "$_src/gpu/GrResourceProvider.cpp",
   "$_src/gpu/GrResourceProvider.h",
+  "$_src/gpu/GrResourceProviderPriv.h",
   "$_src/gpu/GrScissorState.h",
   "$_src/gpu/GrSemaphore.h",
   "$_src/gpu/GrShaderCaps.cpp",