Start two http servers for every configuration

tools/testing/dart/test_progress.dart

 // Copyright (c) 2012, 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 test_progress;
 
 import "dart:io";
 import "dart:io" as io;
 import "http_server.dart" as http_server;
 import "status_file_parser.dart";
@@ skipping 184 matching lines @@
         output.add(decodeUtf8(test.lastCommandOutput.stdout));
       }
     }
     if (!test.lastCommandOutput.stderr.isEmpty) {
       output.add('');
       output.add('stderr:');
       output.add(decodeUtf8(test.lastCommandOutput.stderr));
     }
     if (test is BrowserTestCase) {
       // Additional command for rerunning the steps locally after the fact.
-      output.add('To retest, run: '
-          '${TestUtils.dartTestExecutable.toNativePath()} '
-          '${TestUtils.dartDir().toNativePath()}/tools/testing/dart/'
-          'http_server.dart -m ${test.configuration["mode"]} '
-          '-a ${test.configuration["arch"]} '
-          '-p ${http_server.TestingServerRunner.serverList[0].port} '
-          '-c ${http_server.TestingServerRunner.serverList[1].port} '
-          '--package-root=${http_server.TestingServerRunner.packageRootDir}');
+      var command =
+        test.configuration["_servers_"].httpServerCommandline();
+      output.add('To retest, run:  $command');
     }
     for (Command c in test.commands) {
       output.add('');
       String message = (c == test.commands.last
           ? "Command line" : "Compilation command");
       output.add('$message: ${c.commandLine}');
     }
     return output;
   }
 
@@ skipping 273 matching lines @@
       print('');
       print('$config:');
       statuses.sort((a, b) => a.compareTo(b));
       for (String status in statuses) {
         print('  $status');
       }
     });
     _printStatus();
   }
 }