Update test.dart to use the leg_only option for the leg component.

tools/testing/dart/test_suite.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_suite");
 
 #import("status_file_parser.dart");
 #import("test_runner.dart");
 #import("multitest.dart");
 
@@ skipping 649 matching lines @@
   }
 
   static List<String> standardOptions(Map configuration) {
     List args = ["--ignore-unrecognized-flags"];
     if (configuration["checked"]) {
       args.add('--enable_asserts');
       args.add("--enable_type_checks");
     }
     if (configuration["component"] == "leg") {
       args.add("--enable_leg");
+      args.add("--leg_only");
     }
     if (configuration["component"] == "dartc") {
       if (configuration["mode"] == "release") {
         args.add("--optimize");
       }
     }
     return args;
   }
 }
 
@@ skipping 42 matching lines @@
  * $noCrash tests are expected to be flaky but not crash
  * $pass tests are expected to pass
  * $failOk tests are expected to fail that we won't fix
  * $fail tests are expected to fail that we should fix
  * $crash tests are expected to crash that we should fix
  * $timeout tests are allowed to timeout\
 """;
     print(report);
   }
 }