Add async tracing to SWVersion::AddRequest.

content/browser/background_sync/background_sync_manager.cc

Index: content/browser/background_sync/background_sync_manager.cc
diff --git a/content/browser/background_sync/background_sync_manager.cc b/content/browser/background_sync/background_sync_manager.cc
index b10978dde30e5412951fab805c921d8af67b644d..4cc12bca8d8c7c1a540d15f756a4a18b4342ab2d 100644
--- a/content/browser/background_sync/background_sync_manager.cc
+++ b/content/browser/background_sync/background_sync_manager.cc
@@ -126,8 +126,6 @@ void OnSyncEventFinished(
     int request_id,
     const ServiceWorkerVersion::StatusCallback& callback,
     ServiceWorkerEventStatus status) {
-  TRACE_EVENT1("ServiceWorker", "BackgroundSyncManager::OnSyncEventFinished",
-               "Request id", request_id);
   if (!active_version->FinishRequest(request_id))
     return;
   callback.Run(mojo::ConvertTo<ServiceWorkerStatusCode>(status));