Add constructors to all the event classes.

client/html/src/EventWrappingImplementation.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 EventWrappingImplementation extends DOMWrapperBase implements Event {
+  EventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory EventWrappingImplementation(String type, [bool canBubble = true,
+      bool cancelable = true]) {
+    final e = dom.document.createEvent("Event");
+    e.initEvent(type, canBubble, cancelable);
+    return LevelDom.wrapEvent(e);
+  }
+
+  bool get bubbles() => _ptr.bubbles;
+
+  bool get cancelBubble() => _ptr.cancelBubble;
+
+  void set cancelBubble(bool value) { _ptr.cancelBubble = value; }
+
+  bool get cancelable() => _ptr.cancelable;
+
+  EventTarget get currentTarget() => LevelDom.wrapEventTarget(_ptr.currentTarget);
+
+  bool get defaultPrevented() => _ptr.defaultPrevented;
+
+  int get eventPhase() => _ptr.eventPhase;
+
+  bool get returnValue() => _ptr.returnValue;
+
+  void set returnValue(bool value) { _ptr.returnValue = value; }
+
+  EventTarget get srcElement() => LevelDom.wrapEventTarget(_ptr.srcElement);
+
+  EventTarget get target() => LevelDom.wrapEventTarget(_ptr.target);
+
+  int get timeStamp() => _ptr.timeStamp;
+
+  String get type() => _ptr.type;
+
+  void preventDefault() {
+    _ptr.preventDefault();
+    return;
+  }
+
+  void stopImmediatePropagation() {
+    _ptr.stopImmediatePropagation();
+    return;
+  }
+
+  void stopPropagation() {
+    _ptr.stopPropagation();
+    return;
+  }
+}