Add error-page support in VirtualDirectory.

pkg/http_server/test/virtual_directory_test.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 import 'dart:io';
 
 import "package:unittest/unittest.dart";
 import "package:http_server/http_server.dart";
 
@@ skipping 308 matching lines @@
           return getHeaders(server.port, '/file.jpg')
               .then((headers) => headers.contentType.toString())
               .whenComplete(() {
                 server.close();
                 dir.deleteSync(recursive: true);
               });
         }), completion(equals('image/png')));
       });
     });
   });
+
+  group('error-page', () {
+    test('default', () {
+      expect(HttpServer.bind('localhost', 0).then((server) {
+        var dir = new Directory('').createTempSync();
+        var virDir = new VirtualDirectory(dir.path);
+        dir.deleteSync();
+
+        virDir.serve(server);
+
+        return getAsString(server.port, '/')
+            .whenComplete(() {
+              server.close();
+            });
+      }), completion(matches(new RegExp('404.*Not Found'))));
+    });
+
+    test('custom', () {
+      expect(HttpServer.bind('localhost', 0).then((server) {
+        var dir = new Directory('').createTempSync();
+        var virDir = new VirtualDirectory(dir.path);
+        dir.deleteSync();
+
+        virDir.setErrorPageHandler((request) {
+          request.response.write('my-page ');
+          request.response.write(request.response.statusCode);
+          request.response.close();
+        });
+        virDir.serve(server);
+
+        return getAsString(server.port, '/')
+            .whenComplete(() {
+              server.close();
+            });
+      }), completion(equals('my-page 404')));
+    });
+  });
 }