Move user switcher to backgorund.

Bug: 322745650
Flag: ACONFIG com.android.systemui.flags.Flags.updateUserSwitcherBackground DEVELOPMENT
Test: Local CPU profiling
Change-Id: I12c0c18f332c5b2971aac0b603d202582bc87929
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 407873e..c2072ac 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -429,3 +429,14 @@
        purpose: PURPOSE_BUGFIX
      }
 }
+
+flag {
+    name: "update_user_switcher_background"
+    namespace: "systemui"
+    description: "Decide whether to update user switcher in background thread."
+    bug: "322745650"
+    metadata {
+        purpose: PURPOSE_BUGFIX
+    }
+}
+