Show number of hidden items in new-style list notification.

ui/message_center/views/notification_view_md.h

Index: ui/message_center/views/notification_view_md.h
diff --git a/ui/message_center/views/notification_view_md.h b/ui/message_center/views/notification_view_md.h
index 38ff06dedec0ee26b0d77920adeb954fba7bbdf6..99f5c4aa9cc14337b42301a1b5eabad10169eede 100644
--- a/ui/message_center/views/notification_view_md.h
+++ b/ui/message_center/views/notification_view_md.h
@@ -25,6 +25,10 @@ class BoundedLabel;
 class NotificationHeaderView;
 class ProportionalImageView;
 
+namespace {
+class ItemView;
+}
+
 // View that displays all current types of notification (web, basic, image, and
 // list) except the custom notification. Future notification types may be
 // handled by other classes, in which case instances of those classes would be
@@ -98,7 +102,7 @@ class MESSAGE_CENTER_EXPORT NotificationViewMD
   views::View* image_container_ = nullptr;
   ProportionalImageView* image_view_ = nullptr;
   std::vector<views::LabelButton*> action_buttons_;
-  std::vector<views::View*> item_views_;
+  std::vector<ItemView*> item_views_;
 
   DISALLOW_COPY_AND_ASSIGN(NotificationViewMD);
 };