mark barback test "too_many_open_files_test" as flaky

tests/compiler/dart2js/source_mapping_test.dart

 // Copyright (c) 2012, 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.
 
 import 'dart:async';
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import "../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart";
 import '../../../sdk/lib/_internal/compiler/implementation/source_file.dart';
 import "mock_compiler.dart";
@@ skipping 23 matching lines @@
     buffer.forEachSourceLocation((int offset, var sourcePosition) {
       if (sourcePosition != null && sourcePosition.sourceFile == sourceFile) {
         locations.add(sourcePosition.token.charOffset);
       }
     });
 
     for (int i = 0; i < expectedLocations.length; ++i) {
       int expectedLocation = expectedLocations[i];
       if (!locations.contains(expectedLocation)) {
         int originalLocation = expectedLocation + i;
-        SourceFile sourceFileWithMarkers = new StringSourceFile('<test script>',
-                                                          codeWithMarkers);
+        SourceFile sourceFileWithMarkers =
+            new StringSourceFile('<test script>', codeWithMarkers);
         String message = sourceFileWithMarkers.getLocationMessage(
             'Missing location', originalLocation, originalLocation + 1, true,
             (s) => s);
         Expect.fail(message);
       }
     }
   }));
 }
 
 String FUNCTIONS_TEST = '''
@@ skipping 47 matching lines @@
   testSourceMapLocations(FUNCTIONS_TEST);
   testSourceMapLocations(RETURN_TEST);
   testSourceMapLocations(NOT_TEST);
   testSourceMapLocations(UNARY_TEST);
   testSourceMapLocations(BINARY_TEST);
   testSourceMapLocations(SEND_TEST);
   testSourceMapLocations(SEND_SET_TEST);
   testSourceMapLocations(LOOP_TEST);
   testSourceMapLocations(INTERCEPTOR_TEST);
 }