Add constructors to all the event classes.

client/html/src/Event.dart

Index: client/html/src/Event.dart
diff --git a/client/html/generated/src/interface/Event.dart b/client/html/src/Event.dart
similarity index 75%
rename from client/html/generated/src/interface/Event.dart
rename to client/html/src/Event.dart
index cd7c20579d620348b637b5407b54ef9672249ab1..147d4059530e209e6c62c4476fc35a04b4200028 100644
--- a/client/html/generated/src/interface/Event.dart
+++ b/client/html/src/Event.dart
@@ -2,9 +2,7 @@
 // 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;
 
@@ -44,6 +42,14 @@ interface Event {
 
   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();
@@ -70,8 +76,6 @@ interface Event {
 
   String get type();
 
-  void initEvent(String eventTypeArg, bool canBubbleArg, bool cancelableArg);
-
   void preventDefault();
 
   void stopImmediatePropagation();