Correctly handle the --arch argument to dart test scripts.

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 458 matching lines @@
 
   static String buildDir(Map configuration) {
     var buildDir = '';
     var system = configuration['system'];
     if (system == 'linux') {
       buildDir = 'out/';
     } else if (system == 'macos') {
       buildDir = 'xcodebuild/';
     }
     buildDir += (configuration['mode'] == 'debug') ? 'Debug_' : 'Release_';
-    buildDir += configuration['architecture'] + '/';
+    buildDir += configuration['arch'] + '/';
     return buildDir;
   }
 
   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") {
@@ skipping 53 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);
   }
 }