Remove the Element.prefix setter

Source/core/dom/Element.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 34 matching lines @@
                                                                   [Default=Undefined] optional DOMString localName); // Removed from DOM4.
     [RaisesException, CustomElementCallbacks, DeprecateAs=ElementSetAttributeNodeNS] Attr setAttributeNodeNS([Default=Undefined] optional Attr newAttr); // Removed from DOM4.
     boolean hasAttribute(DOMString name);
     boolean hasAttributeNS(DOMString? namespaceURI, DOMString localName);
 
     [PerWorldBindings] readonly attribute CSSStyleDeclaration style;
 
     // DOM4
     [Reflect] attribute DOMString id;
     readonly attribute DOMString? namespaceURI;
-    [RaisesException=Setter] attribute DOMString? prefix;
+    readonly attribute DOMString? prefix;
     readonly attribute DOMString? localName;
 
     [RaisesException] boolean matches(DOMString selectors);
 
     // Common extensions
 
     readonly attribute long offsetLeft;
     readonly attribute long offsetTop;
     readonly attribute long offsetWidth;
     readonly attribute long offsetHeight;
@@ skipping 59 matching lines @@
     attribute EventHandler onselectstart;
     [RuntimeEnabled=Touch] attribute EventHandler ontouchcancel;
     [RuntimeEnabled=Touch] attribute EventHandler ontouchend;
     [RuntimeEnabled=Touch] attribute EventHandler ontouchmove;
     [RuntimeEnabled=Touch] attribute EventHandler ontouchstart;
     attribute EventHandler onwheel;
 };
 
 Element implements ParentNode;
 Element implements ChildNode;