mark barback test "too_many_open_files_test" as flaky

tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart

Index: tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
diff --git a/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart b/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
index c5a67771d6111bf0cb1e52a902cc51f97f4f5cd4..4ff8edd55a1724d8b7b9adf01b626d3e0d194195 100644
--- a/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
+++ b/tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart
@@ -36,12 +36,9 @@ void main() {
         compiler.deferredLoadTask.allDeferredElements.where((e) => e.isClass())
         .toSet();
 
-    var dateTime =
-        deferredClasses
-            .where((e) => e.name == 'DateTime').single;
+    var dateTime = deferredClasses.where((e) => e.name == 'DateTime').single;
 
-    var myClass =
-        deferredClasses.where((e) => e.name == 'MyClass').single;
+    var myClass = deferredClasses.where((e) => e.name == 'MyClass').single;
 
     var deferredLibrary = compiler.libraries['memory:deferred.dart'];