Allow using '--option value' as well as '--option=value' in dart test script.

tools/testing/dart/test_options.dart

 // Copyright (c) 2011, 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_options_parser");
 
 List<String> defaultTestSelectors =
     const ['dartc', 'samples', 'standalone', 'corelib', 'co19', 'language',
            'isolate', 'stub-generator', 'vm', 'client'];
 
@@ skipping 166 matching lines @@
       var name = '';
       var value = '';
       if (arg.startsWith('--')) {
         if (arg == '--help') {
           _printHelp();
           return null;
         }
         var split = arg.lastIndexOf('=');
         if (split == -1) {
           name = arg;
-          value = '';
+          // Boolean options do not have a value.
+          if (_getSpecification(name).type != 'bool') {
+            if ((i + 1) >= arguments.length) {
+              print('No value supplied for option $name');
+              return null;
+            }
+            value = arguments[++i];
+          }
         } else {
           name = arg.substring(0, split);
           value = arg.substring(split + 1, arg.length);
         }
       } else if (arg.startsWith('-')) {
         if (arg == '-h') {
           _printHelp();
           return null;
         }
         if (arg.length > 2) {
@@ skipping 234 matching lines @@
       if (option.keys.some((key) => key == name)) {
         return option;
       }
     }
     return null;
   }
 
 
   List<_TestOptionSpecification> _options;
 }