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/samplecode/SampleDegenerateQuads.cpp b/samplecode/SampleDegenerateQuads.cpp
index ddf23e7..cdad554 100644
--- a/samplecode/SampleDegenerateQuads.cpp
+++ b/samplecode/SampleDegenerateQuads.cpp
@@ -14,6 +14,7 @@
 #include "include/core/SkPaint.h"
 #include "include/effects/SkDashPathEffect.h"
 #include "include/pathops/SkPathOps.h"
+#include "include/private/SkTPin.h"
 
 // Draw a line through the two points, outset by a fixed length in screen space
 static void draw_extended_line(SkCanvas* canvas, const SkPaint paint,