Add constructors to all the event classes.

client/html/src/CloseEventWrappingImplementation.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 CloseEventWrappingImplementation extends EventWrappingImplementation implements CloseEvent {
+  CloseEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory CloseEventWrappingImplementation(String type, int code, String reason,
+      [bool canBubble = true, bool cancelable = true, bool wasClean = true]) {
+    final e = dom.document.createEvent("CloseEvent");
+    e.initCloseEvent(type, canBubble, cancelable, wasClean, code, reason);
+    return LevelDom.wrapCloseEvent(e);
+  }
+
+  int get code() => _ptr.code;
+
+  String get reason() => _ptr.reason;
+
+  bool get wasClean() => _ptr.wasClean;
+}