Double timeout for slow tests to reduce flakiness seen on travis.

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.
 
 (function() {
   'use strict';
 
   let dart_sdk = dart_library.import('dart_sdk');
   dart_sdk._isolate_helper.startRootIsolate(function() {}, []);
   let async_helper = dart_library.import('async_helper').async_helper;
@@ skipping 734 matching lines @@
           return e;
         }
       }
 
       test(name, function(done) { // 'function' to allow `this.timeout`.
         async_helper.asyncTestInitialize(done);
         console.debug('Running test:  ' + name);
 
         let mainLibrary = dart_library.import(module)[name];
         let negative = /negative_test/.test(name);
-        if (has('slow')) this.timeout(5000);
+        if (has('slow')) this.timeout(10000);
         if (has('fail')) {
           let e = protect(mainLibrary.main);
           if (negative) {
             if (e != null) {
               throw new Error(
                   "negative test marked as 'fail' " +
                   "but passed by throwing:\n" + e);
             }
           } else {
             if (e == null) {
@@ skipping 53 matching lines @@
 
     for (let action of unittest_tests) {
       try {
         action();
       } catch (e) {
         console.error("Caught error tying to setup test:", e);
       }
     }
   });
 })();