Make sure that a drawable replacing a layer in a LayerDrawable gets a callback.

Change-Id: Iefac7d280b3c16e05f45688da655e17e21a3098b

graphics/java/android/graphics/drawable/LayerDrawable.java

@@ -265,6 +265,7 @@ public class LayerDrawable extends Drawable implements Drawable.Callback {
      */
     public boolean setDrawableByLayerId(int id, Drawable drawable) {
         final ChildDrawable[] layers = mLayerState.mChildren;
+        if (drawable != null) drawable.setCallback(mCallback);
         
         for (int i = mLayerState.mNum - 1; i >= 0; i--) {
             if (layers[i].mId == id) {