Revert revision 27014 "Remove restriction on the number of IE processes running simultainiously"

tools/test.dart

 #!/usr/bin/env 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.
 
 /**
  * This file is the entrypoint of the dart test suite.  This suite is used
  * to test:
  *
  *     1. the dart vm
@@ skipping 136 matching lines @@
       serverFutures.add(servers.startServers(conf['local_ip']));
       conf['_servers_'] = servers;
       if (verbose) {
         serverFutures.last.then((_) {
           var commandline = servers.httpServerCommandline();
           print('Started HttpServers: $commandline');
         });
       }
     }
 
-    // If people use selenium they will have issues if we use more than one
-    // ie browser at a time.
-    if (conf['runtime'].startsWith('ie') && !conf['use_browser_controller']) {
+    if (conf['runtime'].startsWith('ie')) {
+      // NOTE: We've experienced random timeouts of tests on ie9/ie10. The
+      // underlying issue has not been determined yet. Our current hypothesis
+      // is that windows does not handle the IE processes independently.
+      // If we have more than one browser and kill a browser we are seeing
+      // issues with starting up a new browser just after killing the hanging
+      // browser.
       maxBrowserProcesses = 1;
     } else if (conf['runtime'].startsWith('safari') &&
                conf['use_browser_controller']) {
       // Safari does not allow us to run from a fresh profile, so we can only
       // use one browser.
       maxBrowserProcesses = 1;
     }
 
     for (String key in selectors.keys) {
       if (key == 'co19') {
@@ skipping 108 matching lines @@
 void main() {
   deleteTemporaryDartDirectories().then((_) {
     var optionsParser = new TestOptionsParser();
     var configurations = optionsParser.parse(new Options().arguments);
     if (configurations != null && configurations.length > 0) {
       testConfigurations(configurations);
     }
   });
 }