Add constructors to all the event classes.

client/html/src/Event.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.
-
-interface Event {
+interface Event factory EventWrappingImplementation {
 
   static final int AT_TARGET = 2;
 
   static final int BLUR = 8192;
 
   static final int BUBBLING_PHASE = 3;
 
   static final int CAPTURING_PHASE = 1;
 
   static final int CHANGE = 32768;
@@ skipping 19 matching lines @@
   static final int MOUSEMOVE = 16;
 
   static final int MOUSEOUT = 8;
 
   static final int MOUSEOVER = 4;
 
   static final int MOUSEUP = 2;
 
   static final int SELECT = 16384;
 
+  // In JS, canBubble and cancelable are technically required parameters to
+  // init*Event. In practice, though, if they aren't provided they simply
+  // default to false (since that's Boolean(undefined)).
+  //
+  // Contrary to JS, we default canBubble and cancelable to true, since that's
+  // what people want most of the time anyway.
+  Event(String type, [bool canBubble, bool cancelable]);
+
   bool get bubbles();
 
   bool get cancelBubble();
 
   void set cancelBubble(bool value);
 
   bool get cancelable();
 
   EventTarget get currentTarget();
 
   bool get defaultPrevented();
 
   int get eventPhase();
 
   bool get returnValue();
 
   void set returnValue(bool value);
 
   EventTarget get srcElement();
 
   EventTarget get target();
 
   int get timeStamp();
 
   String get type();
 
-  void initEvent(String eventTypeArg, bool canBubbleArg, bool cancelableArg);
-
   void preventDefault();
 
   void stopImmediatePropagation();
 
   void stopPropagation();
 }