Drop the crypto dependency.

lib/src/runner/browser/platform.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:async/async.dart';
 import 'package:http_multi_server/http_multi_server.dart';
@@ skipping 31 matching lines @@
     return new BrowserPlatform._(server, config, root: root);
   }
 
   /// The underlying server.
   final shelf.Server _server;
 
   /// A randomly-generated secret.
   ///
   /// This is used to ensure that other users on the same system can't snoop
   /// on data being served through this server.
-  final _secret = randomBase64(24, urlSafe: true);
+  final _secret = Uri.encodeComponent(randomBase64(24));
 
   /// The URL for this server.
   Uri get url => _server.url.resolve(_secret + "/");
 
   /// The test runner configuration.
   Configuration _config;
 
   /// A [OneOffHandler] for servicing WebSocket connections for
   /// [BrowserManager]s.
   ///
@@ skipping 359 matching lines @@
     await Future.wait(futures);
 
     if (_config.pubServeUrl == null) {
       new Directory(_compiledDir).deleteSync(recursive: true);
     } else {
       _http.close();
     }
   });
   final _closeMemo = new AsyncMemoizer();
 }