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/browser/ui/browser_list.h"
+#include "chrome/common/chrome_features.h"
+#include "chrome/common/chrome_switches.h"
+
+// static

[sky, 2016/07/06 16:55:33]

nit: make order match header.

[dgn, 2016/07/22 15:18:09]

Done.

+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 nullptr;
+
+#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 nullptr;
+}
+
+BackgroundModeOptimizer::BackgroundModeOptimizer() : browser_was_added_(false) {
+  KeepAliveRegistry::GetInstance()->AddObserver(this);
+  BrowserList::AddObserver(this);
+}
+
+BackgroundModeOptimizer::~BackgroundModeOptimizer() {
+  KeepAliveRegistry::GetInstance()->RemoveObserver(this);
+  BrowserList::RemoveObserver(this);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+//  KeepAliveRegistry implementation
+
+void BackgroundModeOptimizer::OnKeepAliveStateChanged(bool is_keeping_alive) {
+  // Nothing to do
+}
+
+void BackgroundModeOptimizer::OnKeepAliveRestartStateChanged(bool can_restart) {
+  if (can_restart)
+    TryBrowserRestart();
+}
+///////////////////////////////////////////////////////////////////////////////
+//  BrowserListObserver implementation
+
+void BackgroundModeOptimizer::OnBrowserAdded(Browser* browser) {
+  browser_was_added_ = true;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+//  private methods
+
+void BackgroundModeOptimizer::TryBrowserRestart() {
+  // Avoid unecessary restarts. Whether a browser window has been shown is
+  // our current heuristic to determine if it's worth it.
+  if (!browser_was_added_) {
+    DVLOG(1) << "TryBrowserRestart: Cancelled because no browser was added "
+             << "since the last restart";
+    return;
+  }
+
+  // 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) {
+    DVLOG(1) << "TryBrowserRestart: Cancelled because we are shutting down.";
+    return;
+  }
+
+  DVLOG(1) << "TryBrowserRestart: Making restart attempt.";
+
+  BackgroundModeManager::SetShouldRestartInBackground(true);
+  chrome::AttemptRestart();
+}