SkTypes: extract SkTo

Change-Id: I8de790d5013db2105ad885fa2683303d7c250b09
Reviewed-on: https://skia-review.googlesource.com/133620
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/src/core/SkAAClip.cpp b/src/core/SkAAClip.cpp
index 78c7393..54d6726 100644
--- a/src/core/SkAAClip.cpp
+++ b/src/core/SkAAClip.cpp
@@ -6,12 +6,14 @@
  */
 
 #include "SkAAClip.h"
+
 #include "SkAtomics.h"
 #include "SkBlitter.h"
 #include "SkColorData.h"
-#include "SkRectPriv.h"
 #include "SkPath.h"
+#include "SkRectPriv.h"
 #include "SkScan.h"
+#include "SkTo.h"
 #include "SkUtils.h"
 
 class AutoAAClipValidate {