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 <map>
+
+#include "base/macros.h"
+#include "base/memory/singleton.h"
+
+enum class KeepAliveOrigin;
+
+class KeepAliveRegistry {
+ public:
+  static KeepAliveRegistry* GetInstance();
+
+  bool WillKeepAlive() const;
+
+ private:
+  friend struct base::DefaultSingletonTraits<KeepAliveRegistry>;
+  // Friend to be able to use Register/Unregister
+  friend class ScopedKeepAlive;
+
+  KeepAliveRegistry();
+  ~KeepAliveRegistry();
+
+  // Add/Remove entries. Do not use directly, use ScopedKeepAlive instead.
+  void Register(KeepAliveOrigin origin);
+  void Unregister(KeepAliveOrigin origin);
+
+  // Tracks the registered KeepAlives, storing the origin and the number of
+  // registered KeepAlives for each.
+  std::map<KeepAliveOrigin, int> registered_keep_alives_;
+
+  // Total number of registered KeepAlives
+  int registered_count_;
+
+  DISALLOW_COPY_AND_ASSIGN(KeepAliveRegistry);
+};
+
+#endif  // CHROME_BROWSER_LIFETIME_KEEP_ALIVE_REGISTRY_H_