[PostBoot] Support post boot animation on launcher3

Add ALPHA_CHANNEL_COUNT to DragLayer

Test: manual
Flag: NONE - gated in xml
Bug: 346332241
Change-Id: Ie7cf4c11b4e606e01d54d8a87e7f1dc5906e97b0
diff --git a/src/com/android/launcher3/dragndrop/DragLayer.java b/src/com/android/launcher3/dragndrop/DragLayer.java
index a24f3ff..a826b9e 100644
--- a/src/com/android/launcher3/dragndrop/DragLayer.java
+++ b/src/com/android/launcher3/dragndrop/DragLayer.java
@@ -69,7 +69,9 @@
 public class DragLayer extends BaseDragLayer<Launcher> implements LauncherOverlayCallbacks {
 
     public static final int ALPHA_INDEX_OVERLAY = 0;
-    private static final int ALPHA_CHANNEL_COUNT = 1;
+
+    public static final int ALPHA_INDEX_LOADER = 1;
+    private static final int ALPHA_CHANNEL_COUNT = 2;
 
     public static final int ANIMATION_END_DISAPPEAR = 0;
     public static final int ANIMATION_END_REMAIN_VISIBLE = 2;