Cleaning up event constructors

tools/dom/templates/html/impl/impl_UIEvent.darttemplate

Index: tools/dom/templates/html/impl/impl_UIEvent.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_UIEvent.darttemplate b/tools/dom/templates/html/impl/impl_UIEvent.darttemplate
index 504671a0f639971feafe493271a5a4a9637e153b..939ce85cf614b69cdcaa38d498a02aef3f9f4767 100644
--- a/tools/dom/templates/html/impl/impl_UIEvent.darttemplate
+++ b/tools/dom/templates/html/impl/impl_UIEvent.darttemplate
@@ -13,8 +13,12 @@ $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   //
   // Contrary to JS, we default canBubble and cancelable to true, since that's
   // what people want most of the time anyway.
-  factory $CLASSNAME(String type, Window view, int detail,
-      [bool canBubble = true, bool cancelable = true]) {
+  factory $CLASSNAME(String type,
+      {Window view, int detail: 0, bool canBubble: true,
+      bool cancelable: true}) {
+    if (view == null) {
+      view = window;
+    }
     final e = document.$dom_createEvent("UIEvent");
     e.$dom_initUIEvent(type, canBubble, cancelable, view, detail);
     return e;