Make GrClip.h private

BUG=skia:

Change-Id: I4aa3c2707811ece3a63d161035e316c3bbc1cd15
Reviewed-on: https://skia-review.googlesource.com/9482
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/gn/gpu.gni b/gn/gpu.gni
index e34ff45..59ba257 100644
--- a/gn/gpu.gni
+++ b/gn/gpu.gni
@@ -11,7 +11,6 @@
   "$_include/gpu/GrBlend.h",
   "$_include/gpu/GrBuffer.h",
   "$_include/gpu/GrCaps.h",
-  "$_include/gpu/GrClip.h",
   "$_include/gpu/GrColor.h",
   "$_include/gpu/GrColorSpaceXform.h",
   "$_include/gpu/GrConfig.h",
@@ -77,6 +76,7 @@
   "$_src/gpu/GrBufferAllocPool.cpp",
   "$_src/gpu/GrBufferAllocPool.h",
   "$_src/gpu/GrCaps.cpp",
+  "$_src/gpu/GrClip.h",
   "$_src/gpu/GrClipStackClip.h",
   "$_src/gpu/GrClipStackClip.cpp",
   "$_src/gpu/GrColorSpaceXform.cpp",