Add constructors to all the event classes.

client/html/src/CompositionEventWrappingImplementation.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.
 
-// WARNING: Do not edit - generated code.
+class CompositionEventWrappingImplementation extends UIEventWrappingImplementation implements CompositionEvent {
+  CompositionEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
 
-class CompositionEventWrappingImplementation extends UIEventWrappingImplementation implements CompositionEvent {
-  CompositionEventWrappingImplementation._wrap(ptr) : super._wrap(ptr) {}
+  factory CompositionEventWrappingImplementation(String type, Window view,
+      String data, [bool canBubble = true, bool cancelable = true]) {
+    final e = dom.document.createEvent("CompositionEvent");
+    e.initCompositionEvent(type, canBubble, cancelable, LevelDom.unwrap(view),
+        data);
+    return LevelDom.wrapCompositionEvent(e);
+  }
 
-  String get data() { return _ptr.data; }
-
-  void initCompositionEvent(String typeArg, bool canBubbleArg, bool cancelableArg, Window viewArg, String dataArg) {
-    _ptr.initCompositionEvent(typeArg, canBubbleArg, cancelableArg, LevelDom.unwrap(viewArg), dataArg);
-    return;
-  }
+  String get data() => _ptr.data;
 }