Fix DDC cross-window JS interop on FireFox.

pkg/dev_compiler/test/browser/language_tests.js

 // Copyright (c) 2015, 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.
 
 define(['dart_sdk', 'async_helper', 'expect', 'unittest', 'is', 'require'],
       function(dart_sdk, async_helper, expect, unittest, is, require) {
   'use strict';
 
   async_helper = async_helper.async_helper;
   let minitest = expect.minitest;
@@ skipping 453 matching lines @@
       'indexeddb_1_test': async_unittest,
       'indexeddb_2_test': async_unittest,
       'indexeddb_3_test': async_unittest,
       'indexeddb_4_test': async_unittest,
       'indexeddb_5_test': async_unittest,
       'input_element_test': 'fail', // was sdk#27578, needs triage
       'interactive_test': async_unittest,
       'isolates_test': async_unittest,
 
       'js_interop_1_test': async_unittest,
-      'js_test': firefox_fail,
+
       // Failing because accessing "zSomeInvalidName" does not throw.
       'js_typed_interop_test': 'fail',
 
       // The "typed literal" test fails because the object does not have "_c".
       'js_util_test': 'fail',
       'keyboard_event_test': async_unittest,
 
       'mediasource_test': 'fail', // was sdk#27578, needs triage
       'media_stream_test': 'fail', // was sdk#27578, needs triage
       'messageevent_test': 'fail', // was sdk#27578, needs triage
@@ skipping 357 matching lines @@
 
     for (let action of unittest_tests) {
       try {
         action();
       } catch (e) {
         console.error("Caught error tying to setup test:", e);
       }
     }
   });
 });