Add constructors to all the event classes.

client/html/src/UIEventWrappingImplementation.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 UIEventWrappingImplementation extends EventWrappingImplementation implements UIEvent {
+  UIEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory UIEventWrappingImplementation(String type, Window view, int detail,
+      [bool canBubble = true, bool cancelable = true]) {
+    final e = dom.document.createEvent("UIEvent");
+    e.initUIEvent(type, canBubble, cancelable, LevelDom.unwrap(view), detail);
+    return LevelDom.wrapUIEvent(e);
+  }
+
+  int get charCode() => _ptr.charCode;
+
+  int get detail() => _ptr.detail;
+
+  int get keyCode() => _ptr.keyCode;
+
+  int get layerX() => _ptr.layerX;
+
+  int get layerY() => _ptr.layerY;
+
+  int get pageX() => _ptr.pageX;
+
+  int get pageY() => _ptr.pageY;
+
+  Window get view() => LevelDom.wrapWindow(_ptr.view);
+
+  int get which() => _ptr.which;
+}