Support for running a limited amount of browser tests in parallel

tools/test-runtime.dart

 #!/usr/bin/env 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.
 
 // TODO(ager): Get rid of this version of test.dart when we don't have
 // to worry about the special runtime checkout anymore.
 // This file is identical to test.dart with test suites in the
 // directories samples, client, compiler, and utils removed.
 
@@ skipping 84 matching lines @@
   // The http server is available on localhost:9876 for any
   // test that needs to load resources from the repo over http.
   if (!listTests) {
     // Only start the server if we are running browser tests.
     var runningBrowserTests = configurations.any((config) {
       return TestUtils.isBrowserRuntime(config['runtime']);
     });
     if (runningBrowserTests) startHttpServer('127.0.0.1', 9876);
   }
 
+  var maxBrowserProcesses = maxProcesses;
+
   // Start process queue.
   new ProcessQueue(
       maxProcesses,
+      maxBrowserProcesses,
       progressIndicator,
       startTime,
       printTiming,
       testSuites,
       () => TestingServerRunner.terminateHttpServers(),
       verbose,
       listTests);
 }