Use PrefChangeRegistrar everywhere

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 46e8847cb0dc160209fc2aded58e45a4289354bc..52f37da0bf8c70fc89158e20ed3fac33a2d9df6f 100644
--- a/chrome/browser/background_mode_manager.h
+++ b/chrome/browser/background_mode_manager.h
@@ -8,6 +8,7 @@
 
 #include "app/menus/simple_menu_model.h"
 #include "base/gtest_prod_util.h"
+#include "chrome/browser/prefs/pref_change_registrar.h"
 #include "chrome/browser/status_icons/status_icon.h"
 #include "chrome/common/notification_observer.h"
 #include "chrome/common/notification_registrar.h"
@@ -142,6 +143,9 @@ class BackgroundModeManager
   // Reference to our status icon (if any) - owned by the StatusTray.
   StatusIcon* status_icon_;
 
+  // Ensure observed preferences are properly cleaned up.
+  PrefChangeRegistrar pref_registrar_;
+
   DISALLOW_COPY_AND_ASSIGN(BackgroundModeManager);
 };