Add BackgroundModeOptimizer that can restart the browser

chrome/browser/background/background_mode_optimizer.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/background/background_mode_optimizer.h"
+
+#include "base/command_line.h"
+#include "base/feature_list.h"
+#include "base/memory/ptr_util.h"
+#include "chrome/browser/background/background_mode_manager.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/browser_shutdown.h"
+#include "chrome/browser/lifetime/application_lifetime.h"
+#include "chrome/browser/lifetime/keep_alive_registry.h"
+#include "chrome/common/chrome_features.h"
+#include "chrome/common/chrome_switches.h"
+
+// static
+std::unique_ptr<BackgroundModeOptimizer> BackgroundModeOptimizer::Create() {
+  // If the -keep-alive-for-test flag is passed, then always keep chrome running
+  // in the background until the user explicitly terminates it.
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kKeepAliveForTest))
+    return std::unique_ptr<BackgroundModeOptimizer>();

[sky, 2016/05/18 19:23:06]

nit: return nullptr here and 31.

[dgn, 2016/06/20 17:45:18]

Done.

+
+#if defined(OS_WIN) || defined(OS_LINUX)
+  if (base::FeatureList::IsEnabled(features::kBackgroundModeAllowRestart))
+    return base::WrapUnique(new BackgroundModeOptimizer());
+#endif  // defined(OS_WIN) || defined(OS_LINUX)
+
+  return std::unique_ptr<BackgroundModeOptimizer>();
+}
+
+BackgroundModeOptimizer::BackgroundModeOptimizer() {
+  KeepAliveRegistry::GetInstance()->AddObserver(this);
+}
+
+BackgroundModeOptimizer::~BackgroundModeOptimizer() {
+  KeepAliveRegistry::GetInstance()->RemoveObserver(this);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+//  KeepAliveRegistry implementation
+
+void BackgroundModeOptimizer::OnKeepAliveStateChanged(bool is_keeping_alive) {
+  // Nothing to do
+}
+
+void BackgroundModeOptimizer::OnKeepAliveRestartStateChanged(bool can_restart) {
+  DVLOG(1) << "KeepAliveRestartStateChanged: "
+           << (can_restart ? "Attempting to restart..." : "Nope");
+  if (can_restart)
+    TryBrowserRestart();
+}
+
+///////////////////////////////////////////////////////////////////////////////
+//  private methods
+
+void BackgroundModeOptimizer::TryBrowserRestart() {
+  // If the application is already shutting down, do not turn it into a restart.
+  if (browser_shutdown::IsTryingToQuit() ||
+      browser_shutdown::GetShutdownType() != browser_shutdown::NOT_VALID)
+    return;
+
+  browser_shutdown::SetShouldRestartInBackground(true);
+  chrome::AttemptRestart();
+  g_browser_process->background_mode_manager()->EndBackgroundMode();

[sky, 2016/05/18 19:23:06]

If the restart attempt fails, is the background mode manager then in a weird
state?

[dgn, 2016/06/20 17:45:18]

The restart specific flags are set unconditionally and we check if we can
shutdown afterwards, trying to close browsers, which would affect the KeepAlive
state. We already get here only when the KeepAlive state is favourable. The
other thing is IsTryingToQuit(), but we do check it here.

So the restart attempt should succeed. I'm not sure how to check for restart
failure either, as we don't have return value or other flags that are set when
the whole thing is done. Well, the browser is supposed to restart when that
works.

[sky, 2016/06/20 19:31:55]

I think you should make AttemptRestart return a status. Otherwise it's easy to
break this. Alternatively an observer that is notified if the restart fails.

+}