Fix divider showing when children appear

Fixes: 316155318
Test: send group, send delayed children, open shade
      => see that divider lines do not show
         when child notifs animate in
Flag: EXEMPT bugfix
Change-Id: I7be45d8d4ee0de2a62be35d8904819685295199f
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationChildrenContainer.java b/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationChildrenContainer.java
index 48796d8..b108388 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationChildrenContainer.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationChildrenContainer.java
@@ -634,8 +634,10 @@
     }
 
     private View inflateDivider() {
-        return LayoutInflater.from(mContext).inflate(
+        View divider = LayoutInflater.from(mContext).inflate(
                 R.layout.notification_children_divider, this, false);
+        divider.setAlpha(0f);
+        return divider;
     }
 
     /**