Add constructors to all the event classes.

client/html/src/HashChangeEventWrappingImplementation.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.
+
+class HashChangeEventWrappingImplementation extends EventWrappingImplementation implements HashChangeEvent {
+  HashChangeEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory HashChangeEventWrappingImplementation(String type, String oldURL,
+      String newURL, [bool canBubble = true, bool cancelable = true]) {
+    final e = dom.document.createEvent("HashChangeEvent");
+    e.initHashChangeEvent(type, canBubble, cancelable, oldURL, newURL);
+    return LevelDom.wrapHashChangeEvent(e);
+  }
+
+  String get newURL() => _ptr.newURL;
+
+  String get oldURL() => _ptr.oldURL;
+}