Animate notification shade footer

Fixes: 187958424
Test: visual
Change-Id: I7adef54a713b856afce0c20b58850a239545881b

packages/SystemUI/src/com/android/systemui/statusbar/notification/row/FooterView.java

@@ -115,13 +115,18 @@ public class FooterView extends StackScrollerDecorView {
     }
 
     public class FooterViewState extends ExpandableViewState {
+        /**
+         * used to hide the content of the footer to animate.
+         * #hide is applied without animation, but #hideContent has animation.
+         */
+        public boolean hideContent;
+
         @Override
         public void applyToView(View view) {
             super.applyToView(view);
             if (view instanceof FooterView) {
                 FooterView footerView = (FooterView) view;
-                boolean visible = this.clipTopAmount < mClearAllTopPadding;
-                footerView.setContentVisible(visible && footerView.isVisible());
+                footerView.setContentVisible(!hideContent);
             }
         }
     }

packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/StackScrollAlgorithm.java

@@ -411,8 +411,8 @@ public class StackScrollAlgorithm {
             final float footerEnd = algorithmState.mCurrentExpandedYPosition
                     + view.getIntrinsicHeight();
             final boolean noSpaceForFooter = footerEnd > ambientState.getStackEndHeight();
-
-            viewState.hidden = shadeClosed || isShelfShowing || noSpaceForFooter;
+            ((FooterView.FooterViewState) viewState).hideContent =
+                    shadeClosed || isShelfShowing || noSpaceForFooter;
 
         } else if (view != ambientState.getTrackedHeadsUpRow()) {
             if (ambientState.isExpansionChanging()) {