Add missing new file

base/cxx20_to_address.h

diff --git a/base/cxx20_to_address.h b/base/cxx20_to_address.h
new file mode 100644
index 0000000..56a87b7
--- /dev/null
+++ b/base/cxx20_to_address.h
@@ -0,0 +1,31 @@
+// Copyright 2021 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_CXX20_TO_ADDRESS_H_
+#define BASE_CXX20_TO_ADDRESS_H_
+
+#include <type_traits>
+
+namespace gurl_base {
+
+// Simplified C++14 implementation of C++20's std::to_address.
+// Note: This does not consider specializations of pointer_traits<>::to_address,
+// since that member function may only be present in C++20 and later.
+//
+// Reference: https://wg21.link/pointer.conversion#lib:to_address
+template <typename T>
+constexpr T* to_address(T* p) noexcept {
+  static_assert(!std::is_function<T>::value,
+                "Error: T must not be a function type.");
+  return p;
+}
+
+template <typename Ptr>
+constexpr auto to_address(const Ptr& p) noexcept {
+  return to_address(p.operator->());
+}
+
+}  // namespace base
+
+#endif  // BASE_CXX20_TO_ADDRESS_H_