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

client/html/src/OverflowEvent.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 OverflowEvent extends Event factory OverflowEventWrappingImplementation {
+interface OverflowEvent extends Event default OverflowEventWrappingImplementation {
 
   OverflowEvent(int orient, bool horizontalOverflow, bool verticalOverflow);
 
   static final int BOTH = 2;
 
   static final int HORIZONTAL = 0;
 
   static final int VERTICAL = 1;
 
   bool get horizontalOverflow();
 
   int get orient();
 
   bool get verticalOverflow();
 }