Remove Node.prefix so it's no longer visible to script.

Source/core/frame/UseCounter.h

 /*
  * Copyright (C) 2012 Google, Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 162 matching lines @@
         DocumentCreateAttribute, // Removed from DOM4.
         DocumentCreateAttributeNS, // Removed from DOM4.
         DocumentCreateCDATASection, // Removed from DOM4.
         DocumentInputEncoding, // Removed from DOM4.
         DocumentXMLEncoding, // Removed from DOM4.
         DocumentXMLStandalone, // Removed from DOM4.
         DocumentXMLVersion, // Removed from DOM4.
         NodeIsSameNode, // Removed from DOM4.
         NodeIsSupported, // Removed from DOM4.
         NodeNamespaceURI, // Removed from DOM4.
-        NodePrefix, // Removed from DOM4.
+        UnusedSlot06, // Removed, was Node.prefix.
         NodeLocalName, // Removed from DOM4.
         NavigatorProductSub,
         NavigatorVendor,
         NavigatorVendorSub,
         FileError,
         DocumentCharset, // Documented as IE extensions, from KHTML days.
         PrefixedAnimationEndEvent,
         UnprefixedAnimationEndEvent,
         PrefixedAndUnprefixedAnimationEndEvent,
         PrefixedAnimationStartEvent,
@@ skipping 82 matching lines @@
         HTMLElementOuterText,
         ReplaceDocumentViaJavaScriptURL,
         ElementSetAttributeNodeNS, // Removed from DOM4.
         ElementPrefixedMatchesSelector,
         DOMImplementationCreateCSSStyleSheet,
         CSSStyleSheetRules,
         CSSStyleSheetAddRule,
         CSSStyleSheetRemoveRule,
         InitMessageEvent,
         PrefixedInitMessageEvent,
+        ElementSetPrefix, // Element.prefix is readonly in DOM4.
         // Add new features immediately above this line. Don't change assigned
         // numbers of each items, and don't reuse unused slots.
         NumberOfFeatures, // This enum value must be last.
     };
 
     // "count" sets the bit for this feature to 1. Repeated calls are ignored.
     static void count(const Document&, Feature);
     static void count(const ExecutionContext*, Feature);
     void count(CSSParserContext, CSSPropertyID);
     void count(Feature);
@@ skipping 35 matching lines @@
 
     void updateMeasurements();
 
     OwnPtr<BitVector> m_countBits;
     BitVector m_CSSFeatureBits;
 };
 
 } // namespace WebCore
 
 #endif // UseCounter_h