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

mojo/public/tools/bindings/generators/cpp_templates/enum_macros.tmpl

 {#---
   Macro for enum definition, and the declaration of associated functions.
 ---#}
 
 {%- macro enum_decl(enum) %}
 {%-   set enum_name = enum|get_name_for_kind(flatten_nested_kind=True) %}
 enum class {{enum_name}} : int32_t {
 {%-   for field in enum.fields %}
 {%-     if field.value %}
   {{field.name}} = {{field.value|expression_to_text}},
@@ skipping 77 matching lines @@
           flatten_nested_kind=True, include_variant=False) %}
 {%-   set hash_fn_name = enum|wtf_hash_fn_name_for_enum %}
 {#    We need two unused enum values: #}
 {%-   set empty_value = -1000000 %}
 {%-   set deleted_value = -1000001 %}
 {%-   set empty_value_unused = "false" if empty_value in enum|all_enum_values else "true" %}
 {%-   set deleted_value_unused = "false" if empty_value in enum|all_enum_values else "true" %}
 namespace WTF {
 struct {{hash_fn_name}} {
   static unsigned hash(const {{enum_name}}& value) {
-    typedef base::underlying_type<{{enum_name}}>::type utype;
+    using utype = std::underlying_type<{{enum_name}}>::type;
     return DefaultHash<utype>::Hash().hash(static_cast<utype>(value));
   }
   static bool equal(const {{enum_name}}& left, const {{enum_name}}& right) {
     return left == right;
   }
   static const bool safeToCompareToEmptyOrDeleted = true;
 };
 
 template <>
 struct DefaultHash<{{enum_name}}> {
@@ skipping 13 matching lines @@
   }
   static void constructDeletedValue({{enum_name}}& slot, bool) {
     slot = static_cast<{{enum_name}}>({{deleted_value}});
   }
   static bool isDeletedValue(const {{enum_name}}& value) {
     return value == static_cast<{{enum_name}}>({{deleted_value}});
   }
 };
 }  // namespace WTF
 {%- endmacro %}