Expose UserTrackerImpl initialize function

Bug: 276914935
Test: build
Change-Id: I7da2b914ff8795d427bce4f26c7fad4829d2c050
diff --git a/packages/SystemUI/src/com/android/systemui/settings/UserTrackerImpl.kt b/packages/SystemUI/src/com/android/systemui/settings/UserTrackerImpl.kt
index 0b2ae05..7cbc32f 100644
--- a/packages/SystemUI/src/com/android/systemui/settings/UserTrackerImpl.kt
+++ b/packages/SystemUI/src/com/android/systemui/settings/UserTrackerImpl.kt
@@ -103,7 +103,7 @@
     @GuardedBy("callbacks")
     private val callbacks: MutableList<DataItem> = ArrayList()
 
-    fun initialize(startingUser: Int) {
+    open fun initialize(startingUser: Int) {
         if (initialized) {
             return
         }