Add BackgroundModeOptimizer that can restart the browser

chrome/browser/browser_shutdown.cc

Index: chrome/browser/browser_shutdown.cc
diff --git a/chrome/browser/browser_shutdown.cc b/chrome/browser/browser_shutdown.cc
index ab8f9d7561797948661f840a633e867733a84666..d20e541135cdc9c59ed1868048e46f5fea280ea0 100644
--- a/chrome/browser/browser_shutdown.cc
+++ b/chrome/browser/browser_shutdown.cc
@@ -47,6 +47,10 @@
 #include "chrome/browser/first_run/upgrade_util.h"
 #endif
 
+#if BUILDFLAG(ENABLE_BACKGROUND)
+#include "chrome/browser/background/background_mode_manager.h"
+#endif
+
 #if defined(ENABLE_RLZ)
 #include "components/rlz/rlz_tracker.h"
 #endif
@@ -194,7 +198,7 @@ bool ShutdownPreThreadsStop() {
   return restart_last_session;
 }
 
-void ShutdownPostThreadsStop(bool restart_last_session) {
+void ShutdownPostThreadsStop(int shutdown_flags) {
   delete g_browser_process;
   g_browser_process = NULL;
 
@@ -214,7 +218,7 @@ void ShutdownPostThreadsStop(bool restart_last_session) {
   }
 #endif
 
-  if (restart_last_session) {
+  if (shutdown_flags & RESTART_LAST_SESSION) {
 #if !defined(OS_CHROMEOS)
     // Make sure to relaunch the browser with the original command line plus
     // the Restore Last Session flag. Note that Chrome can be launched (ie.
@@ -239,6 +243,8 @@ void ShutdownPostThreadsStop(bool restart_last_session) {
       else
         new_cl->AppendSwitch(it.first);
     }
+    if (shutdown_flags & RESTART_IN_BACKGROUND)
+      new_cl->AppendSwitch(switches::kNoStartupWindow);
 
 #if defined(OS_POSIX) || defined(OS_WIN)
     upgrade_util::RelaunchChromeBrowser(*new_cl.get());
@@ -329,6 +335,22 @@ void ReadLastShutdownInfo() {
 
 void SetTryingToQuit(bool quitting) {
   g_trying_to_quit = quitting;
+
+  if (quitting)
+    return;
+
+  // Reset the restart-related preferences.

[sky, 2016/07/22 16:57:52]

This just documents what the code is doing. Instead document why this code is
here. Why do you need to reset restart-related preferences?

[dgn, 2016/07/25 17:32:28]

Done.

+  PrefService* pref_service = g_browser_process->local_state();
+  if (pref_service) {
+#if !defined(OS_ANDROID)
+    pref_service->ClearPref(prefs::kWasRestarted);
+#endif  // !defined(OS_ANDROID)
+    pref_service->ClearPref(prefs::kRestartLastSessionOnShutdown);
+  }
+
+#if BUILDFLAG(ENABLE_BACKGROUND)
+  BackgroundModeManager::should_restart_in_background(false);
+#endif  // BUILDFLAG(ENABLE_BACKGROUND)
 }
 
 bool IsTryingToQuit() {