Remove defaultSelected property.

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

 // Copyright (c) 2013, 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.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
-  factory OptionElement({String data, String value, bool defaultSelected, 
-      bool selected}) {
-    return new OptionElement._(data, value, defaultSelected, selected);
+  factory OptionElement({String data, String value, bool selected: false}) {
+    return new OptionElement._(data, value, false, selected);
   }
 $!MEMBERS
 }