Implement platform deleters per spec.

Source/core/dom/DatasetDOMStringMap.h

 /*
  * Copyright (C) 2010 Apple 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 30 matching lines @@
         return adoptPtr(new DatasetDOMStringMap(element));
     }
 
     virtual void ref();
     virtual void deref();
 
     virtual void getNames(Vector<String>&);
     virtual String item(const String& name);
     virtual bool contains(const String& name);
     virtual void setItem(const String& name, const String& value, ExceptionState&);
-    virtual void deleteItem(const String& name, ExceptionState&);
+    virtual bool deleteItem(const String& name);
 
     virtual Element* element() { return m_element; }
 
 private:
     explicit DatasetDOMStringMap(Element* element)
         : m_element(element)
     {
     }
 
     Element* m_element;
 };
 
 } // namespace WebCore
 
 #endif // DatasetDOMStringMap_h