Cleanup some constexpr nits in base/numerics

base/numerics/safe_math_impl.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_NUMERICS_SAFE_MATH_IMPL_H_
 #define BASE_NUMERICS_SAFE_MATH_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 97 matching lines @@
 };
 
 template <typename Numeric>
 struct UnsignedOrFloatForSize<Numeric, false, true> {
   typedef Numeric type;
 };
 
 // Helper templates for integer manipulations.
 
 template <typename T>
-bool HasSignBit(T x) {
+constexpr bool HasSignBit(T x) {
   // Cast to unsigned since right shift on signed is undefined.
   return !!(static_cast<typename UnsignedIntegerForSize<T>::type>(x) >>
             PositionOfSignBit<T>::value);
 }
 
 // This wrapper undoes the standard integer promotions.
 template <typename T>
-T BinaryComplement(T x) {
+constexpr T BinaryComplement(T x) {
   return static_cast<T>(~x);
 }
 
 // Here are the actual portable checked integer math implementations.
 // TODO(jschuh): Break this code out from the enable_if pattern and find a clean
 // way to coalesce things into the CheckedNumericState specializations below.
 
 template <typename T>
 typename std::enable_if<std::numeric_limits<T>::is_integer, T>::type
 CheckedAdd(T x, T y, RangeConstraint* validity) {
@@ skipping 386 matching lines @@
                             sizeof(T) >= (2 * sizeof(Lhs)) &&
                             StaticDstRangeRelationToSrcRange<T, Rhs>::value !=
                                 NUMERIC_RANGE_CONTAINED &&
                             sizeof(T) >= (2 * sizeof(Rhs));
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_MATH_IMPL_H_