Moves over remaining .dart code references to 'factory' in interface declartions to 'default'

client/html/src/UIEvent.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.
 
-interface UIEvent extends Event factory UIEventWrappingImplementation {
+interface UIEvent extends Event default UIEventWrappingImplementation {
 
   UIEvent(String type, Window view, int detail, [bool canBubble,
       bool cancelable]);
 
   int get charCode();
 
   int get detail();
 
   int get keyCode();
 
   int get layerX();
 
   int get layerY();
 
   int get pageX();
 
   int get pageY();
 
   Window get view();
 
   int get which();
 }