Initialize background visibility of ActivatableNotificationView

Initializes the background visibilities that were previously
only set when adding the view to the scroller,
resulting in HUNs having two backgrounds.

Bug: 15106201
Change-Id: I21ef3b34c6feb0e852c9dc2c3289665cff40927e

packages/SystemUI/src/com/android/systemui/statusbar/ActivatableNotificationView.java

@@ -149,6 +149,7 @@ public abstract class ActivatableNotificationView extends ExpandableOutlineView
         super.onFinishInflate();
         mBackgroundNormal = (NotificationBackgroundView) findViewById(R.id.backgroundNormal);
         mBackgroundDimmed = (NotificationBackgroundView) findViewById(R.id.backgroundDimmed);
+        updateBackground();
         updateBackgroundResources();
     }