Remove the --use_browser_controller flag, now that it is always true.

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 147 matching lines @@
     }
 
     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']) {
+    } else if (conf['runtime'].startsWith('safari')) {
       // Safari does not allow us to run from a fresh profile, so we can only
       // use one browser.
       maxBrowserProcesses = 1;
     } else if (conf['runtime'] == 'chrome' &&
-               conf['use_browser_controller'] &&
                Platform.operatingSystem == 'macos') {
       // Chrome on mac results in random timeouts.
       maxBrowserProcesses = math.max(1, maxBrowserProcesses ~/ 2);
     }
 
     for (String key in selectors.keys) {
       if (key == 'co19') {
         testSuites.add(new Co19TestSuite(conf));
       } else if (conf['runtime'] == 'vm' && key == 'vm') {
         // vm tests contain both cc tests (added here) and dart tests (added
@@ skipping 102 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);
     }
   });
 }