Refactor InsettableFrameLayout/DragLayer and add StateListener interface.

Bug: 65387919
Change-Id: I5eb94c0f3962d44f63af3efc92d852e019bba711
diff --git a/src/com/android/launcher3/dragndrop/DragLayer.java b/src/com/android/launcher3/dragndrop/DragLayer.java
index 8189b23..9f9822c 100644
--- a/src/com/android/launcher3/dragndrop/DragLayer.java
+++ b/src/com/android/launcher3/dragndrop/DragLayer.java
@@ -703,13 +703,14 @@
     }
 
     @Override
-    public void onChildViewAdded(View parent, View child) {
-        super.onChildViewAdded(parent, child);
+    public void onViewAdded(View child) {
+        super.onViewAdded(child);
         updateChildIndices();
     }
 
     @Override
-    public void onChildViewRemoved(View parent, View child) {
+    public void onViewRemoved(View child) {
+        super.onViewRemoved(child);
         updateChildIndices();
     }