Make Dart test scripts work for the VM on Windows.

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");
 
 interface TestSuite {
@@ skipping 263 matching lines @@
 
     return { "vmOptions": result,
              "dartOptions": dartOptions,
              "isNegative" : isNegative };
   }
 }
 
 
 class TestUtils {
   static String executableName(Map configuration) {
+    String postfix =
+        (new Platform().operatingSystem() == 'windows') ? '.exe' : '';
     switch (configuration['component']) {
       case 'vm':
-        return 'dart';
+        return 'dart$postfix';
       case 'dartc':
-        return 'compiler/bin/dartc_test';
+        return 'compiler/bin/dartc_test$postfix';
       case 'frog':
       case 'leg':
-          return 'frog/bin/frog';
+          return 'frog/bin/frog$postfix';
       case 'frogsh':
-        return 'frog/bin/frogsh';
+        return 'frog/bin/frogsh$postfix';
       default:
         throw "Unknown executable for: ${configuration['component']}";
     }
   }
 
 
   static String dartShellFileName(Map configuration) {
     var name = buildDir(configuration) + executableName(configuration);
     if (!(new File(name)).existsSync()) {
       throw "Executable '$name' does not exist";
@@ skipping 24 matching lines @@
       args.add("--enable_leg");
     }
     if (configuration["component"] == "dartc") {
       if (configuration["mode"] == "release") {
         args.add("--optimize");
       }
     }
     return args;
   }
 }