Make THEME_CATEGORIES public

Bug: 182345292
Test: n/a
Change-Id: Ib6cd18c8633a74ba207f345692b2ccd2357e7adf
diff --git a/src/com/android/customization/model/theme/ThemeManager.java b/src/com/android/customization/model/theme/ThemeManager.java
index 533fbd0..85241c1 100644
--- a/src/com/android/customization/model/theme/ThemeManager.java
+++ b/src/com/android/customization/model/theme/ThemeManager.java
@@ -43,7 +43,7 @@
 
 public class ThemeManager implements CustomizationManager<ThemeBundle> {
 
-    private static final Set<String> THEME_CATEGORIES = new HashSet<>();
+    public static final Set<String> THEME_CATEGORIES = new HashSet<>();
     static {
         THEME_CATEGORIES.add(OVERLAY_CATEGORY_COLOR);
         THEME_CATEGORIES.add(OVERLAY_CATEGORY_FONT);