Add factory constructor for WebSocket Add generated dom & html directories to .gitignore

client/html/src/frog_FactoryProviders.dart

 // Copyright (c) 2012, 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.
 
 class _AudioContextFactoryProvider {
 
   factory AudioContext() native '''
     var constructor = window.AudioContext || window.webkitAudioContext;
     return new constructor();
 ''';
@@ skipping 47 matching lines @@
   static Uint32Array _U32(arg) native 'return new Uint32Array(arg);';
   static Uint8ClampedArray _U8C(arg) native 'return new Uint8ClampedArray(arg);';
 
   static ensureNative(List list) => list;  // TODO: make sure.
 }
 
 class _PointFactoryProvider {
 
   factory Point(num x, num y) native 'return new WebKitPoint(x, y);';
 }
+
+class _WebSocketFactoryProvider {
+
+  factory WebSocket(String url) native '''return new WebSocket(url);''';
+}