Remove base::underlying_type, replace uses with std::underlying_type

base/numerics/safe_conversions_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_CONVERSIONS_IMPL_H_
 #define BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
 
 #include <stdint.h>
 
 #include <limits>
@@ skipping 499 matching lines @@
   static_assert(IsIntegerArithmeticSafe<type, Lhs, Rhs>::value, "");
   static const bool is_contained = true;
 };
 
 template <typename Lhs, typename Rhs>
 struct FastIntegerArithmeticPromotion<Lhs, Rhs, false> {
   using type = typename BigEnoughPromotion<Lhs, Rhs>::type;
   static const bool is_contained = false;
 };
 
-// This hacks around libstdc++ 4.6 missing stuff in type_traits.
-#if defined(__GLIBCXX__)
-#define PRIV_GLIBCXX_4_7_0 20120322
-#define PRIV_GLIBCXX_4_5_4 20120702
-#define PRIV_GLIBCXX_4_6_4 20121127
-#if (__GLIBCXX__ < PRIV_GLIBCXX_4_7_0 || __GLIBCXX__ == PRIV_GLIBCXX_4_5_4 || \
-     __GLIBCXX__ == PRIV_GLIBCXX_4_6_4)
-#define PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX
-#undef PRIV_GLIBCXX_4_7_0
-#undef PRIV_GLIBCXX_4_5_4
-#undef PRIV_GLIBCXX_4_6_4
-#endif
-#endif
-
 // Extracts the underlying type from an enum.
 template <typename T, bool is_enum = std::is_enum<T>::value>
 struct ArithmeticOrUnderlyingEnum;
 
 template <typename T>
 struct ArithmeticOrUnderlyingEnum<T, true> {
-#if defined(PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX)
-  using type = __underlying_type(T);
-#else
   using type = typename std::underlying_type<T>::type;
-#endif
   static const bool value = std::is_arithmetic<type>::value;
 };
 
-#if defined(PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX)
-#undef PRIV_USE_FALLBACKS_FOR_OLD_GLIBCXX
-#endif
-
 template <typename T>
 struct ArithmeticOrUnderlyingEnum<T, false> {
   using type = T;
   static const bool value = std::is_arithmetic<type>::value;
 };
 
 // The following are helper templates used in the CheckedNumeric class.
 template <typename T>
 class CheckedNumeric;
 
@@ skipping 161 matching lines @@
                    static_cast<BigType>(static_cast<L>(lhs)),
                    static_cast<BigType>(static_cast<R>(rhs)))
              // Let the template functions figure it out for mixed types.
              : C<L, R>::Test(lhs, rhs);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_