Add ScopedKeepAlive to c/b/lifetime

chrome/browser/lifetime/keep_alive_registry.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/keep_alive_registry.h"
+
+#include "chrome/browser/lifetime/application_lifetime.h"
+#include "chrome/browser/lifetime/keep_alive_types.h"
+
+////////////////////////////////////////////////////////////////////////////////
+// Public methods
+
+// static
+KeepAliveRegistry* KeepAliveRegistry::GetInstance() {
+  return base::Singleton<KeepAliveRegistry>::get();
+}
+
+bool KeepAliveRegistry::WillKeepAlive() const {
+  return registered_count_ > 0;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Private methods
+
+KeepAliveRegistry::KeepAliveRegistry() : registered_count_(0) {}
+
+KeepAliveRegistry::~KeepAliveRegistry() {
+  DCHECK_EQ(0, registered_count_);
+  DCHECK_EQ(0u, registered_keep_alives_.size());
+}
+
+void KeepAliveRegistry::Register(KeepAliveOrigin origin) {
+  if (!WillKeepAlive())
+    chrome::IncrementKeepAliveCount();
+
+  auto count_per_origin_it = registered_keep_alives_.find(origin);

[sky, 2016/02/25 18:43:50]

Is there a reason you converted away from the simpler
registered_keep_alives_[origin]++ ?

[dgn, 2016/02/25 20:08:49]

I wanted to be sure about the initial value in the map. I searched around and
did not find much detailing the expected behavior. Just searched again and found
http://stackoverflow.com/a/9025981 which explains that the standard specifies it
should be 0 though. I'll change it back.

[dgn, 2016/02/26 11:51:59]

Done.

+  if (count_per_origin_it == registered_keep_alives_.end())
+    registered_keep_alives_.insert(std::make_pair(origin, 1));
+  else
+    ++count_per_origin_it->second;
+
+  ++registered_count_;
+}
+
+void KeepAliveRegistry::Unregister(KeepAliveOrigin origin) {
+  --registered_count_;
+  DCHECK_GE(registered_count_, 0);
+
+  int new_count = --registered_keep_alives_[origin];
+  DCHECK_GE(registered_keep_alives_[origin], 0);
+  if (new_count == 0)
+    registered_keep_alives_.erase(origin);
+
+  if (!WillKeepAlive())
+    chrome::DecrementKeepAliveCount();
+}