Merge "Add documentation about threading."

core/java/android/service/notification/NotificationAssistantService.java

@@ -52,6 +52,9 @@ import java.util.List;
  * {@link #onNotificationEnqueued(StatusBarNotification)} will only be called for notifications
  * sent to the current user, and {@link Adjustment adjuments} will only be accepted for the
  * current user.
+ * <p>
+ *     All callbacks are called on the main thread.
+ * </p>
  *
  * @hide
  */

core/java/android/service/notification/NotificationListenerService.java

@@ -91,6 +91,10 @@ import java.util.List;
  * notification listeners running in a work profile. A
  * {@link android.app.admin.DevicePolicyManager} might block notifications originating from a work
  * profile.</p>
+ * <p>
+ *     From {@link Build.VERSION_CODES#N} onward all callbacks are called on the main thread. Prior
+ *     to N, there is no guarantee on what thread the callback will happen.
+ * </p>
  */
 public abstract class NotificationListenerService extends Service {