Add "Keep chrome running in background" preference.

chrome/browser/background_mode_manager.h

Index: chrome/browser/background_mode_manager.h
diff --git a/chrome/browser/background_mode_manager.h b/chrome/browser/background_mode_manager.h
index 236637f62e5d369750a36f57fc3c5593fb6cd2c2..171f463620dab607c99169bd0d3a20191d42fa1b 100644
--- a/chrome/browser/background_mode_manager.h
+++ b/chrome/browser/background_mode_manager.h
@@ -46,7 +46,6 @@ class BackgroundModeManager
   BackgroundModeManager(Profile* profile, CommandLine* command_line);
   virtual ~BackgroundModeManager();
 
-  static bool IsBackgroundModeEnabled(const CommandLine* command_line);
   static void RegisterPrefs(PrefService* prefs);
 
  private:
@@ -146,7 +145,23 @@ class BackgroundModeManager
   // window.
   Browser* GetBrowserWindow();
 
+  // Returns true if the "Let chrome run in the background" pref is checked.
+  bool IsBackgroundModePrefEnabled();
+
+  // Turns off background mode if it's currently enabled.
+  void DisableBackgroundMode();
+
+  // Turns on background mode if it's currently disabled.
+  void EnableBackgroundMode();
+
+  // Returns true if background mode is permanently disabled for this chrome
+  // session.
+  static bool IsBackgroundModePermanentlyDisabled(
+      const CommandLine* command_line);
+
+  // Registrars for managing our change observers.
   NotificationRegistrar registrar_;
+  PrefChangeRegistrar pref_registrar_;
 
   // The parent profile for this object.
   Profile* profile_;