Add BackgroundModeOptimizer that can restart the browser

chrome/browser/browser_shutdown.h

Index: chrome/browser/browser_shutdown.h
diff --git a/chrome/browser/browser_shutdown.h b/chrome/browser/browser_shutdown.h
index c3450329d821fe916384dc5a6e38d406e7dfe58e..e3cf6506841d13a1bcdb9817be6c1a14c77dda57 100644
--- a/chrome/browser/browser_shutdown.h
+++ b/chrome/browser/browser_shutdown.h
@@ -11,6 +11,20 @@ class PrefRegistrySimple;
 
 namespace browser_shutdown {
 
+// Shutdown flags
+enum Flags {
+  NO_FLAGS = 0,
+
+  // If |RESTART_LAST_SESSION| is set, the browser will attempt to restart in
+  // in the last session after the shutdown.
+  RESTART_LAST_SESSION = 1 << 0,
+
+  // Makes a panned restart happen in the background. The browser will just come
+  // up in the system tray but not open a new window after restarting. This flag
+  // has no effect if |RESTART_LAST_SESSION| is not set.
+  RESTART_IN_BACKGROUND = 1 << 1
+};
+
 enum ShutdownType {
   // an uninitialized value
   NOT_VALID = 0,
@@ -41,9 +55,8 @@ bool ShutdownPreThreadsStop();
 // Performs the remaining shutdown tasks after all threads but the
 // main thread have been stopped.  This includes deleting g_browser_process.
 //
-// The provided parameter indicates whether a preference to restart
-// the session was present.
-void ShutdownPostThreadsStop(bool restart_last_session);
+// See |browser_shutdown::Flags| for the possible flag values and their effects.
+void ShutdownPostThreadsStop(int shutdown_flags);
 #endif
 
 // Called at startup to create a histogram from our previous shutdown time.