Remove webkitdropzone.

third_party/WebKit/Source/core/html/HTMLElement.idl

 /*
  * Copyright (C) 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 45 matching lines @@
     // CSS Object Model (CSSOM)
     // https://dev.w3.org/csswg/cssom/#the-elementcssinlinestyle-interface
     [SameObject, PerWorldBindings, PutForwards=cssText] readonly attribute CSSStyleDeclaration style;
     // Typed OM
     // https://drafts.css-houdini.org/css-typed-om/#inline-stylepropertymap-objects
     [RuntimeEnabled=CSSTypedOM] readonly attribute StylePropertyMap styleMap;
 
     // Non-standard APIs
     [TreatNullAs=NullString, CEReactions, CustomElementCallbacks, RaisesException=Setter, MeasureAs=HTMLElementInnerText] attribute DOMString innerText;
     [TreatNullAs=NullString, CEReactions, CustomElementCallbacks, RaisesException=Setter, MeasureAs=HTMLElementOuterText] attribute DOMString outerText;
-    [CEReactions, Reflect, TreatNullAs=NullString, MeasureAs=PrefixedHTMLElementDropzone] attribute DOMString webkitdropzone;
 };
 
 HTMLElement implements GlobalEventHandlers;