Add constructors to all the event classes.

client/html/src/AnimationEventWrappingImplementation.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 AnimationEventWrappingImplementation extends EventWrappingImplementation implements AnimationEvent {
+  static String _name;
+
+  AnimationEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  static String get _eventName() {
+    if (_name != null) return _name;
+
+    try {
+      dom.document.createEvent("WebKitAnimationEvent");
+      _name = "WebKitAnimationEvent";
+    } catch (var e) {
+      _name = "AnimationEvent";
+    }
+    return _name;
+  }
+
+  factory AnimationEventWrappingImplementation(String type, String propertyName,
+      double elapsedTime, [bool canBubble = true, bool cancelable = true]) {
+    final e = dom.document.createEvent(_eventName);
+    e.initWebKitAnimationEvent(
+        type, canBubble, cancelable, propertyName, elapsedTime);
+    return LevelDom.wrapAnimationEvent(e);
+  }
+
+  String get animationName() => _ptr.animationName;
+
+  num get elapsedTime() => _ptr.elapsedTime;
+}