Add ptr_util.h from base until std::make_unique<> available

third_party/base/ptr_util.h

+// Copyright 2016 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 PDFIUM_THIRD_PARTY_BASE_PTR_UTIL_H_
+#define PDFIUM_THIRD_PARTY_BASE_PTR_UTIL_H_
+
+#include <memory>
+#include <utility>
+
+namespace pdfium {
+
+// Helper to transfer ownership of a raw pointer to a std::unique_ptr<T>.
+// Note that std::unique_ptr<T> has very different semantics from
+// std::unique_ptr<T[]>: do not use this helper for array allocations.
+template <typename T>
+std::unique_ptr<T> WrapUnique(T* ptr) {
+  return std::unique_ptr<T>(ptr);
+}
+
+namespace internal {
+
+template <typename T>
+struct MakeUniqueResult {
+  using Scalar = std::unique_ptr<T>;
+};
+
+template <typename T>
+struct MakeUniqueResult<T[]> {
+  using Array = std::unique_ptr<T[]>;
+};
+
+template <typename T, size_t N>
+struct MakeUniqueResult<T[N]> {
+  using Invalid = void;
+};
+
+}  // namespace internal
+
+// Helper to construct an object wrapped in a std::unique_ptr. This is an
+// implementation of C++14's std::MakeUnique that can be used in Chrome.
+//
+// MakeUnique<T>(args) should be preferred over WrapUnique(new T(args)): bare
+// calls to `new` should be treated with scrutiny.
+//
+// Usage:
+//   // ptr is a std::unique_ptr<std::string>
+//   auto ptr = MakeUnique<std::string>("hello world!");
+//
+//   // arr is a std::unique_ptr<int[]>
+//   auto arr = MakeUnique<int[]>(5);
+
+// Overload for non-array types. Arguments are forwarded to T's constructor.
+template <typename T, typename... Args>
+typename internal::MakeUniqueResult<T>::Scalar MakeUnique(Args&&... args) {
+  return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
+}
+
+// Overload for array types of unknown bound, e.g. T[]. The array is allocated
+// with `new T[n]()` and value-initialized: note that this is distinct from
+// `new T[n]`, which default-initializes.
+template <typename T>
+typename internal::MakeUniqueResult<T>::Array MakeUnique(size_t size) {
+  return std::unique_ptr<T>(new typename std::remove_extent<T>::type[size]());
+}
+
+// Overload to reject array types of known bound, e.g. T[n].
+template <typename T, typename... Args>
+typename internal::MakeUniqueResult<T>::Invalid MakeUnique(Args&&... args) =
+    delete;
+
+}  // namespace pdfium
+
+#endif  // PDFIUM_THIRD_PARTY_BASE_PTR_UTIL_H_