Add ScopedKeepAlive to c/b/lifetime

chrome/browser/lifetime/keep_alive_registry.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 CHROME_BROWSER_LIFETIME_KEEP_ALIVE_REGISTRY_H_
+#define CHROME_BROWSER_LIFETIME_KEEP_ALIVE_REGISTRY_H_
+
+#include <set>
+
+#include "base/macros.h"
+#include "base/memory/singleton.h"
+
+struct KeepAliveOptions;
+
+class KeepAliveRegistry {
+ public:
+  static KeepAliveRegistry* GetInstance();
+
+  void Register(const KeepAliveOptions* options);
+  void Unregister(const KeepAliveOptions* options);
+
+ private:
+  friend struct base::DefaultSingletonTraits<KeepAliveRegistry>;
+
+  KeepAliveRegistry();
+  ~KeepAliveRegistry();
+
+  std::multiset<const KeepAliveOptions*> registered_keep_alives_;
+
+  DISALLOW_COPY_AND_ASSIGN(KeepAliveRegistry);
+};
+
+#endif  // CHROME_BROWSER_LIFETIME_KEEP_ALIVE_REGISTRY_H_