Update from https://crrev.com/316786

base/bind_helpers.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.
 
 // This defines a set of argument wrappers and related factory methods that
 // can be used specify the refcounting and reference semantics of arguments
 // that are bound by the Bind() function in base/bind.h.
 //
 // It also defines a set of simple functions and utilities that people want
 // when using Callback<> and Bind().
@@ skipping 517 matching lines @@
 
 template <typename... Types1, typename... Types2>
 struct ConcatTypeListsImpl<TypeList<Types1...>, TypeList<Types2...>> {
   typedef TypeList<Types1..., Types2...> Type;
 };
 
 // A type-level function that concats two TypeLists.
 template <typename List1, typename List2>
 using ConcatTypeLists = typename ConcatTypeListsImpl<List1, List2>::Type;
 
-template <size_t n, typename List>
-struct NthTypeImpl;
-
-template <size_t n, typename T, typename... Types>
-struct NthTypeImpl<n, TypeList<T, Types...>>
-    : NthTypeImpl<n - 1, TypeList<Types...>> {
-};
-
-template <typename T, typename... Types>
-struct NthTypeImpl<0, TypeList<T, Types...>> {
-  typedef T Type;
-};
-
-// A type-level function that extracts |n|th type from a TypeList.
-template <size_t n, typename List>
-using NthType = typename NthTypeImpl<n, List>::Type;
-
 // Used for MakeFunctionType implementation.
 template <typename R, typename ArgList>
 struct MakeFunctionTypeImpl;
 
 template <typename R, typename... Args>
 struct MakeFunctionTypeImpl<R, TypeList<Args...>> {
   typedef R(Type)(Args...);
 };
 
 // A type-level function that constructs a function type that has |R| as its
@@ skipping 45 matching lines @@
 BASE_EXPORT void DoNothing();
 
 template<typename T>
 void DeletePointer(T* obj) {
   delete obj;
 }
 
 }  // namespace base
 
 #endif  // BASE_BIND_HELPERS_H_