Continued low-priority group implementation

Adapting the low-priority group implementation
according to spec. Expanding a group takes 2 taps now.

Test: add low-priority group observe behavior
Change-Id: Ic563a8fe0e71df746b9b548adc8d1698940b1a83
Fixes: 35125708
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/stack/ViewState.java b/packages/SystemUI/src/com/android/systemui/statusbar/stack/ViewState.java
index e0a6159..624fd3b 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/stack/ViewState.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/stack/ViewState.java
@@ -136,7 +136,7 @@
         yTranslation = view.getTranslationY();
         zTranslation = view.getTranslationZ();
         gone = view.getVisibility() == View.GONE;
-        hidden = false;
+        hidden = view.getVisibility() == View.INVISIBLE;
         scaleX = view.getScaleX();
         scaleY = view.getScaleY();
     }