Disable 20s unittest timeout for docs_test and dartdoc_test.

tools/dom/docs/test/docs_test.dart

 // Copyright (c) 2013, 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.
 
 library docs_test;
 
 import 'dart:io';
 
 import 'package:unittest/unittest.dart';
 import 'package:path/path.dart' as path;
 
 import '../bin/docs.dart';
 import '../lib/docs.dart';
 
 final testJsonPath = path.normalize(path.join(scriptDir, 'test.json'));
 
 main() {
+  // Some tests take more than the default 20 second unittest timeout.
+  unittestConfiguration.timeout = null;
   group('docs', () {
     var oldJson = new File(json_path);
     var testJson = new File(testJsonPath);
 
     tearDown(() {
       // Clean up.
       if (testJson.existsSync()) {
         testJson.deleteSync();
       }
       assert(!testJson.existsSync());
@@ skipping 19 matching lines @@
 
         // Ensure that there's nothing different between the new JSON and old.
         expect(testJson.readAsStringSync(), equals(oldJson.readAsStringSync()));
 
         // Ensure that the old JSON file didn't actually change.
         expect(oldJsonModified, equals(oldJson.lastModifiedSync()));
       }), completes);
     });
   });
 }