Support 'Conditional' idl attribute.

client/dom/generated/src/interface/HTMLElement.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.
 
 // WARNING: Do not edit - generated code.
 
 interface HTMLElement extends Element {
 
   String get accessKey();
 
@@ skipping 30 matching lines @@
   String get innerHTML();
 
   void set innerHTML(String value);
 
   String get innerText();
 
   void set innerText(String value);
 
   bool get isContentEditable();
 
-  String get itemId();
-
-  void set itemId(String value);
-
-  DOMSettableTokenList get itemProp();
-
-  DOMSettableTokenList get itemRef();
-
-  bool get itemScope();
-
-  void set itemScope(bool value);
-
-  DOMSettableTokenList get itemType();
-
-  Object get itemValue();
-
-  void set itemValue(Object value);
-
   String get lang();
 
   void set lang(String value);
 
   String get outerHTML();
 
   void set outerHTML(String value);
 
   String get outerText();
 
@@ skipping 14 matching lines @@
   String get webkitdropzone();
 
   void set webkitdropzone(String value);
 
   Element insertAdjacentElement(String where, Element element);
 
   void insertAdjacentHTML(String where, String html);
 
   void insertAdjacentText(String where, String text);
 }