Add ScopedKeepAlive to c/b/lifetime

chrome/browser/lifetime/scoped_keep_alive.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_SCOPED_KEEP_ALIVE_H_
+#define CHROME_BROWSER_LIFETIME_SCOPED_KEEP_ALIVE_H_
+
+#include "base/macros.h"
+
+enum class KeepAliveOrigin;
+
+// Registers with KeepAliveRegistry on creation and unregisters them
+// on destruction. Use these objects with a scoped_ptr for easy management.
+class ScopedKeepAlive {
+ public:
+  explicit ScopedKeepAlive(KeepAliveOrigin origin);
+  ~ScopedKeepAlive();
+
+ private:
+  const KeepAliveOrigin origin_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedKeepAlive);
+};
+
+#endif  // CHROME_BROWSER_LIFETIME_SCOPED_KEEP_ALIVE_H_