Revert "Revert "SkTypes: extract SkTo""

This reverts commit fdcfb8b7c23fbf18f872d2c31d27978235033876.

> Original change's description:
> > SkTypes: extract SkTo
> >
> > Change-Id: I8de790d5013db2105ad885fa2683303d7c250b09
> > Reviewed-on: https://skia-review.googlesource.com/133620
> > Reviewed-by: Mike Klein <mtklein@google.com>

Change-Id: Ida74fbc5c21248a724a5edbf9fae18a33bcb23aa
Reviewed-on: https://skia-review.googlesource.com/134506
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index 4c82e50..3d471d1 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -18,6 +18,7 @@
 #ifndef SkPaint_DEFINED
 #define SkPaint_DEFINED
 
+#include "../private/SkTo.h"
 #include "SkBlendMode.h"
 #include "SkColor.h"
 #include "SkFilterQuality.h"