Added getIconSize method to PreviewLayoutRule interface.

This will be used in new Folder animation.

Bug: 35064148
Change-Id: I5573336c0b8a9db8d1e600b1e16de07f48f35a21

src/com/android/launcher3/folder/StackFolderIconLayoutRule.java

@@ -86,6 +86,11 @@ public class StackFolderIconLayoutRule implements FolderIcon.PreviewLayoutRule {
         return MAX_NUM_ITEMS_IN_PREVIEW;
     }
 
+    @Override
+    public float getIconSize() {
+        return mBaselineIconSize;
+    }
+
     @Override
     public float scaleForItem(int index, int numItems) {
         // Scale is determined by the position of the icon in the preview.