Support creating progress bar notification for Windows

ui/message_center/notification.h

Index: ui/message_center/notification.h
diff --git a/ui/message_center/notification.h b/ui/message_center/notification.h
index 23e2e8c53fefebd30840466a5e8513db74fca9c4..4217ac4dbdd31c871de2172cc3f7184e1b3268a9 100644
--- a/ui/message_center/notification.h
+++ b/ui/message_center/notification.h
@@ -44,6 +44,7 @@ class MESSAGE_CENTER_EXPORT RichNotificationData {
   string16 expanded_message;
   gfx::Image image;
   std::vector<NotificationItem> items;
+  int progress;
   std::vector<ButtonInfo> buttons;
 };
 
@@ -88,6 +89,7 @@ class MESSAGE_CENTER_EXPORT Notification {
   const std::vector<NotificationItem>& items() const {
     return optional_fields_.items;
   }
+  int progress() const { return optional_fields_.progress; }
   // End unpacked values.
 
   // Images fetched asynchronously.