Send media controller code to background thread.

Flag: com.android.systemui.notification_media_manager_background_execution
Bug: 336612071
Test: manual.
Test: atest SystemUiRoboTests:NotificationMediaManagerTest
Change-Id: I8c3f6fbcfdf94d87ed5a9c3f2de8035ef49680c9
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 36bad5e..9c20345 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -1012,3 +1012,13 @@
      purpose: PURPOSE_BUGFIX
    }
 }
+
+flag {
+  name: "notification_media_manager_background_execution"
+  namespace: "systemui"
+  description: "Decide whether to execute binder calls in background thread"
+  bug: "336612071"
+  metadata {
+    purpose: PURPOSE_BUGFIX
+  }
+}