Fix problems with closures_test.

pkg/kernel/test/closures/testing.json

 {
 "":"Copyright (c) 2016, 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.md file.",
   "packages": "../../../../.packages",
   "suites": [
     {
       "name": "closures",
       "kind": "Chain",
       "source": "suite.dart",
-      "path": "../../testcases/closures",
+      "path": "../../testcases/closures/",
       "status": "closures.status",
       "pattern": [
         "\\.dart$"
       ],
       "exclude": [
         "/test/closures/suite\\.dart$"
       ]
     }
   ],
   "analyze": {
     "uris": [
       "suite.dart"
     ],
     "exclude": [
     ]
   }
 }