wtf/CheckedArithmetic.h delegates to base/numerics/safe_math.h.

third_party/WebKit/Source/wtf/CheckedNumeric.h

Index: third_party/WebKit/Source/wtf/CheckedNumeric.h
diff --git a/third_party/WebKit/Source/wtf/NotFound.h b/third_party/WebKit/Source/wtf/CheckedNumeric.h
similarity index 83%
copy from third_party/WebKit/Source/wtf/NotFound.h
copy to third_party/WebKit/Source/wtf/CheckedNumeric.h
index 7c7d0c3cfb4c0ba231534d750da4b56161542463..bae31f3537b13e9c3d7705ef5859a150e912572e 100644
--- a/third_party/WebKit/Source/wtf/NotFound.h
+++ b/third_party/WebKit/Source/wtf/CheckedNumeric.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008 Apple Inc. All Rights Reserved.
+ * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -23,13 +23,15 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef NotFound_h
-#define NotFound_h
+#ifndef WTF_CheckedNumeric_h
+#define WTF_CheckedNumeric_h
 
-namespace WTF {
-const size_t kNotFound = static_cast<size_t>(-1);
-}
+/* See base/numerics/safe_math.h for usage.
+ */
+#include "base/numerics/safe_math.h"
 
-using WTF::kNotFound;
+namespace WTF {
+using base::CheckedNumeric;
+} // namespace WTF
 

[Yuta Kitamura, 2016/03/17 08:19:08]

We usually add "using WTF::CheckedNumeric" in the global
namespace, too, so the user code doesn't have to put "WTF::".

[Bret, 2016/03/18 20:48:51]

Done.

-#endif // NotFound_h
+#endif