Add support for CheckedNumeric Max and Min constexpr functions

base/numerics/safe_conversions.h

Index: base/numerics/safe_conversions.h
diff --git a/base/numerics/safe_conversions.h b/base/numerics/safe_conversions.h
index 71408102eabc4843493cf46e086129c766dcce8e..7dca58781a1d2afd040b1433082dfc8011a9e2d0 100644
--- a/base/numerics/safe_conversions.h
+++ b/base/numerics/safe_conversions.h
@@ -42,6 +42,8 @@ namespace base {
 //      across any range of arithmetic types. StrictNumeric is the return type
 //      for values extracted from a CheckedNumeric class instance. The raw
 //      arithmetic value is extracted via static_cast to the underlying type.
+//  StrictNum() - Creates a new StrictNumeric from the underlying type of the
+//          supplied arithmetic or StrictNumeric type.
 
 // Convenience function that returns true if the supplied value is in range
 // for the destination type.
@@ -229,6 +231,13 @@ class StrictNumeric {
   const T value_;
 };
 
+// Convience wrapper returns a StrictNumeric from the provided arithmetic type.
+template <typename T>
+constexpr StrictNumeric<typename UnderlyingType<T>::type> StrictNum(

[dcheng, 2016/12/03 21:34:29]

Nit: usually we name the deducing helpers MakeFoo, e.g. MakeUnique or
make_scoped_refptr. I think that's what I'd personally prefer to see in the
base/numerics interface for consitency.

[jschuh, 2016/12/03 22:29:12]

Fair. I'll fix it here and convert CheckNum to MakeChecked in another CL as
well. 

[dcheng, 2016/12/04 01:42:14]

MakeStrict / MakeChecked almost feel too generic (it's not obvious they have
anything to do with arithmetic without context). But I'm happy to bikeshed in
the followup.

+    const T value) {
+  return value;
+}
+
 // Overload the ostream output operator to make logging work nicely.
 template <typename T>
 std::ostream& operator<<(std::ostream& os, const StrictNumeric<T>& value) {
@@ -258,6 +267,7 @@ STRICT_COMPARISON_OP(IsNotEqual, !=);
 using internal::strict_cast;
 using internal::saturated_cast;
 using internal::StrictNumeric;
+using internal::StrictNum;
 
 // Explicitly make a shorter size_t typedef for convenience.
 typedef StrictNumeric<size_t> SizeT;