fix ddc travis bot

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',
         'test_status'],
       function(dart_sdk, async_helper, expect, unittest, is, require,
                test_status) {
   'use strict';
 
@@ skipping 212 matching lines @@
       'big_integer_arith_vm_test_mul_multi': fail,
       'big_integer_arith_vm_test_negate_multi': fail,
       'big_integer_arith_vm_test_none_multi': fail,
       'big_integer_arith_vm_test_overflow_multi': fail,
       'big_integer_arith_vm_test_shift_multi': fail,
       'big_integer_arith_vm_test_sub_multi': fail,
       'big_integer_arith_vm_test_trunDiv_multi': fail,
       'big_integer_parsed_arith_vm_test': fail,
       'big_integer_parsed_div_rem_vm_test': fail,
       'big_integer_parsed_mul_div_vm_test': fail,
-
       'bit_twiddling_bigint_test': fail,
       'collection_length_test': skip_timeout,
       'compare_to2_test': fail,
       'const_list_literal_test': fail,
       'const_list_remove_range_test': fail,
       'const_list_set_range_test': fail,
       'core_runtime_types_test': fail,
       'date_time10_test': fail,
       'double_parse_test_02_multi': firefox_fail,
+      'error_stack_trace_test_nullThrown_multi': fail,
+      'list_unmodifiable_test': fail, // DDC is throwing a strong mode error, so it may be a test bug
       'for_in_test': is.firefox('<=50') ? fail : pass,
       'growable_list_test': fail,
       'hash_map2_test': skip_timeout,
       'hash_set_test_01_multi': fail,
       'int_modulo_arith_test_bignum_multi': fail,
       'int_modulo_arith_test_modPow_multi': fail,
       'int_modulo_arith_test_none_multi': fail,
       'int_parse_radix_test_01_multi': fail, // JS implementations disagree on U+0085 being whitespace.
       'int_parse_radix_test_02_multi': ['fail', 'timeout', 'skip'], // No bigints.
       'int_parse_radix_test_none_multi': ['slow'],
@@ skipping 609 matching lines @@
 
     for (let action of unittest_tests) {
       try {
         action();
       } catch (e) {
         console.error("Caught error tying to setup test:", e);
       }
     }
   });
 });