Add base::Reversed() as an adapter for range-based for loops in reverse

base/containers/adapters_unittest.cc

Index: base/containers/adapters_unittest.cc
diff --git a/base/containers/adapters_unittest.cc b/base/containers/adapters_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c1891da3f0747a5c8429020e6af9eabeb31dfee0
--- /dev/null
+++ b/base/containers/adapters_unittest.cc
@@ -0,0 +1,40 @@
+// 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.
+
+#include "base/containers/adapters.h"
+
+#include <vector>
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+TEST(AdaptersTest, Reversed) {
+  std::vector<int> v;
+  v.push_back(3);
+  v.push_back(2);
+  v.push_back(1);
+  int j = 0;
+  for (int& i : base::reversed(v)) {
+    EXPECT_EQ(++j, i);
+    i += 100;
+  }
+  EXPECT_EQ(103, v[0]);
+  EXPECT_EQ(102, v[1]);
+  EXPECT_EQ(101, v[2]);
+}
+
+TEST(AdaptersTest, ConstReversed) {
+  std::vector<int> v;
+  v.push_back(3);
+  v.push_back(2);
+  v.push_back(1);
+  const std::vector<int>& cv = v;
+  int j = 0;
+  for (int i : base::reversed(cv)) {
+    EXPECT_EQ(++j, i);
+  }
+}
+
+}  // namespace