Merge "Use alpha instead of invisible for views below shelf to skip redraw" into sc-dev

        shelf.updateState(algorithmState, ambientState);

        // After the shelf has updated its yTranslation,

        // explicitly hide views below the shelf to skip rendering them in the hardware layer.

        // After the shelf has updated its yTranslation, explicitly set alpha=0 for view below shelf

        // to skip rendering them in the hardware layer. We do not set them invisible because that

        // runs invalidate & onDraw when these views return onscreen, which is more expensive.

        final float shelfTop = shelf.getViewState().yTranslation;

        for (ExpandableView view : algorithmState.visibleChildren) {

            if (view instanceof ExpandableNotificationRow) {

                ExpandableNotificationRow row = (ExpandableNotificationRow) view;

                if (row.isHeadsUp() || row.isHeadsUpAnimatingAway()) {

                    continue;

                }

            }

            final float viewTop = view.getViewState().yTranslation;

            if (viewTop >= shelfTop) {

                view.getViewState().hidden = true;

                view.getViewState().alpha = 0;

            }

        }

    }