move SkTPin to include/private

Change-Id: Ib0dc823d331a7cddc5da1d1be83136ce803a7871
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/327783
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/src/gpu/GrDistanceFieldGenFromVector.cpp b/src/gpu/GrDistanceFieldGenFromVector.cpp
index a677482..fc8b892 100644
--- a/src/gpu/GrDistanceFieldGenFromVector.cpp
+++ b/src/gpu/GrDistanceFieldGenFromVector.cpp
@@ -11,6 +11,7 @@
 #include "include/core/SkMatrix.h"
 #include "include/gpu/GrConfig.h"
 #include "include/pathops/SkPathOps.h"
+#include "include/private/SkTPin.h"
 #include "src/core/SkAutoMalloc.h"
 #include "src/core/SkGeometry.h"
 #include "src/core/SkPointPriv.h"