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

base/template_util.h

 // Copyright (c) 2011 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_TEMPLATE_UTIL_H_
 #define BASE_TEMPLATE_UTIL_H_
 
 #include <stddef.h>
 #include <iosfwd>
 #include <type_traits>
@@ skipping 46 matching lines @@
 template <typename T, typename = void>
 struct SupportsOstreamOperator : std::false_type {};
 template <typename T>
 struct SupportsOstreamOperator<T,
                                decltype(void(std::declval<std::ostream&>()
                                              << std::declval<T>()))>
     : std::true_type {};
 
 }  // namespace internal
 
-// underlying_type produces the integer type backing an enum type.
-// TODO(crbug.com/554293): Remove this when all platforms have this in the std
-// namespace.
-#if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX)
-template <typename T>
-struct underlying_type {
-  using type = __underlying_type(T);
-};
-#else
-template <typename T>
-using underlying_type = std::underlying_type<T>;
-#endif
-
 // TODO(crbug.com/554293): Remove this when all platforms have this in the std
 // namespace.
 #if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX)
 template <class T>
 using is_trivially_destructible = std::has_trivial_destructor<T>;
 #else
 template <class T>
 using is_trivially_destructible = std::is_trivially_destructible<T>;
 #endif
 
@@ skipping 40 matching lines @@
 using is_trivially_copyable = std::is_trivially_copyable<T>;
 #endif
 
 }  // namespace base
 
 #undef CR_USE_FALLBACKS_FOR_OLD_GLIBCXX
 #undef CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX
 #undef CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX
 
 #endif  // BASE_TEMPLATE_UTIL_H_