Add BackgroundModeOptimizer that can restart the browser

chrome/browser/browser_shutdown.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_BROWSER_SHUTDOWN_H_
 #define CHROME_BROWSER_BROWSER_SHUTDOWN_H_
 
 #include "build/build_config.h"
 
 class PrefRegistrySimple;
@@ skipping 25 matching lines @@
 // BrowserProcess and the various threads go away.
 //
 // Returns true if the session should be restarted.
 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);
+void ShutdownPostThreadsStop(bool restart_last_session,

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

nit: use bitmask to improve readability. Also, document what
restart_in_background means.

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

Done.

+                             bool restart_in_background);
 #endif
 
 // Called at startup to create a histogram from our previous shutdown time.
 void ReadLastShutdownInfo();
 
 // There are various situations where the browser process should continue to
 // run after the last browser window has closed - the Mac always continues
 // running until the user explicitly quits, and on Windows/Linux the application
 // should not shutdown when the last browser window closes if there are any
 // BackgroundContents running.
@@ skipping 14 matching lines @@
 bool IsTryingToQuit();
 
 // Starts to collect shutdown traces. On ChromeOS this will start immediately
 // on AttemptUserExit() and all other systems will start once all tabs are
 // closed.
 void StartShutdownTracing();
 
 }  // namespace browser_shutdown
 
 #endif  // CHROME_BROWSER_BROWSER_SHUTDOWN_H_