Use Expect.throws for directory test

tests/standalone/src/DirectoryTest.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.
 //
 // Directory listing test.
 
 class DirectoryTest {
   static void testListing() {
     bool listedDir = false;
     bool listedFile = false;
@@ skipping 246 matching lines @@
   if (os == "windows") {
     return "*";
   }
   return null;
 }
 
 
 testCreateTempErrorSync() {
   var location = illegalTempDirectoryLocation();
   if (location != null) {
-    bool exception = false;
-    try {
-      new Directory(location).createTempSync();
-    } catch(DirectoryException e) {
-      exception = true;
-    }
-    Expect.isTrue(exception);
+    Expect.throws(new Directory(location).createTempSync,
+                  (e) => e is DirectoryException);
   }
 }
 
 
 testCreateTempError() {
   var location = illegalTempDirectoryLocation();
   if (location == null) return;
 
   var resultPort = new ReceivePort.singleShot();
   resultPort.receive((String message, ignored) {
       Expect.equals("error", message);
     });
 
   Directory dir = new Directory(location);
   dir.errorHandler = (error) { resultPort.toSendPort().send("error"); };
   dir.createTempHandler = () { resultPort.toSendPort().send("success"); };
   dir.createTemp();
 }
 
 
 main() {
   DirectoryTest.testMain();
   NestedTempDirectoryTest.testMain();
   testCreateTempErrorSync();
   testCreateTempError();
 }