Import Reversed adapter from Chromium and use it in v8.

src/base/adapters.h

+// Copyright 2014 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.
+
+// Slightly adapted for inclusion in V8.
+// Copyright 2014 the V8 project authors. All rights reserved.
+
+#ifndef V8_BASE_ADAPTERS_H_
+#define V8_BASE_ADAPTERS_H_
+
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace base {
+
+// Internal adapter class for implementing base::Reversed.
+template <typename T>
+class ReversedAdapter {
+ public:
+  typedef decltype(static_cast<T*>(nullptr)->rbegin()) Iterator;
+
+  explicit ReversedAdapter(T& t) : t_(t) {}
+  ReversedAdapter(const ReversedAdapter& ra) : t_(ra.t_) {}
+
+  Iterator begin() const { return t_.rbegin(); }
+  Iterator end() const { return t_.rend(); }
+
+ private:
+  T& t_;
+
+  DISALLOW_ASSIGN(ReversedAdapter);
+};
+
+// Reversed returns a container adapter usable in a range-based "for" statement
+// for iterating a reversible container in reverse order.
+//
+// Example:
+//
+//   std::vector<int> v = ...;
+//   for (int i : base::Reversed(v)) {
+//     // iterates through v from back to front
+//   }
+template <typename T>
+ReversedAdapter<T> Reversed(T& t) {
+  return ReversedAdapter<T>(t);
+}
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_ADAPTERS_H_