One more minor mixin fix

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 173 matching lines @@
       'left_shift_test': fail,
       'list_is_test': fail,
       'list_literal3_test': fail,
       'many_generic_instanceof_test': fail,
       'many_named_arguments_test': whitelist,
       'map_literal10_test': fail,
       'map_literal7_test': fail,
       'memory_swap_test': skip_timeout,
       'method_invocation_test': fail,
       'mint_arithmetic_test': fail,
-      'mixin_implements_test': fail,
-      'mixin_regress_13688_test': fail,
       'mixin_super_constructor_positionals_test_none_multi': fail, // Issue 28059
       'modulo_test': fail,
       'named_parameter_clash_test': fail,
       'named_parameters_passing_falsy_test': is.firefox('<=50') ? fail : pass,
       'nan_identical_test': fail,
       'nested_switch_label_test': fail,
       'number_identifier_test_05_multi': fail,
       'number_identity2_test': fail,
       'numbers_test': fail,
       'redirecting_factory_reflection_test': fail,
@@ skipping 717 matching lines @@
 
     for (let action of unittest_tests) {
       try {
         action();
       } catch (e) {
         console.error("Caught error tying to setup test:", e);
       }
     }
   });
 });