Add ScopedKeepAlive to c/b/lifetime

chrome/browser/lifetime/scoped_keep_alive.cc

+// 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.
+
+#include "chrome/browser/lifetime/scoped_keep_alive.h"
+
+#include "chrome/browser/lifetime/keep_alive_registry.h"
+#include "chrome/browser/lifetime/keep_alive_types.h"
+
+ScopedKeepAlive::ScopedKeepAlive(KeepAliveOrigin origin) : origin_(origin) {
+  KeepAliveRegistry::GetInstance()->Register(origin_);
+}
+
+ScopedKeepAlive::~ScopedKeepAlive() {
+  KeepAliveRegistry::GetInstance()->Unregister(origin_);
+}