Share MediaStorageUtil common code among platforms.

chrome/browser/system_monitor/removable_device_notifications_mac.h

Index: chrome/browser/system_monitor/removable_device_notifications_mac.h
diff --git a/chrome/browser/system_monitor/removable_device_notifications_mac.h b/chrome/browser/system_monitor/removable_device_notifications_mac.h
index 70a3e19162ae39f4eda2d63bf0c79ac0b0ee5f57..aa6f31ab2ef789c7723d61a0d75ca48015e035ce 100644
--- a/chrome/browser/system_monitor/removable_device_notifications_mac.h
+++ b/chrome/browser/system_monitor/removable_device_notifications_mac.h
@@ -15,6 +15,9 @@
 
 namespace chrome {
 
+class RemovableDeviceNotificationsMac;
+typedef RemovableDeviceNotificationsMac RemovableDeviceNotifications;
+
 // This class posts notifications to base::SystemMonitor when a new disk
 // is attached, removed, or changed.
 class RemovableDeviceNotificationsMac :
@@ -26,9 +29,12 @@ class RemovableDeviceNotificationsMac :
     UPDATE_DEVICE_REMOVED,
   };
 
+  // Should only be called by browser start up code.  Use GetInstance() instead.
   RemovableDeviceNotificationsMac();
   virtual ~RemovableDeviceNotificationsMac();
 
+  static RemovableDeviceNotificationsMac* GetInstance();
+
   void UpdateDisk(const DiskInfoMac& info, UpdateType update_type);
 
   bool GetDeviceInfoForPath(