mark barback test "too_many_open_files_test" as flaky

tests/compiler/dart2js/deferred_load_graph_segmentation_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Test of the graph segmentation algorithm used by deferred loading
 // to determine which elements can be deferred and which libraries
 // much be included in the initial download (loaded eagerly).
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
@@ skipping 18 matching lines @@
                                    ['--analyze-only']);
   asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
     var main = compiler.mainApp.find(dart2js.Compiler.MAIN);
     Expect.isNotNull(main, "Could not find 'main'");
     compiler.deferredLoadTask.onResolutionComplete(main);
 
     var deferredClasses =
         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'];
 
     Expect.equals(deferredLibrary, myClass.getLibrary());
     Expect.equals(compiler.coreLibrary, dateTime.declaration.getLibrary());
   }));
 }
 
 const Map MEMORY_SOURCE_FILES = const {
   'main.dart': """
@@ skipping 16 matching lines @@
 class MyClass {
   const MyClass();
 
   foo(x) {
     new DateTime.now();
     return (x - 3) ~/ 2;
   }
 }
 """,
 };