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/GrMemoryPool.cpp b/src/gpu/GrMemoryPool.cpp
index 2cdb6fa..d1d2c82 100644
--- a/src/gpu/GrMemoryPool.cpp
+++ b/src/gpu/GrMemoryPool.cpp
@@ -7,6 +7,7 @@
 
 #include "src/gpu/GrMemoryPool.h"
 
+#include "include/private/SkTPin.h"
 #include "src/gpu/ops/GrOp.h"
 
 #ifdef SK_DEBUG