Implement platform deleters per spec.

Source/core/dom/DatasetDOMStringMap.cpp

 /*
  * 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 170 matching lines @@
 void DatasetDOMStringMap::setItem(const String& name, const String& value, ExceptionState& exceptionState)
 {
     if (!isValidPropertyName(name)) {
         exceptionState.throwDOMException(SyntaxError, ExceptionMessages::failedToSet(name, "DOMStringMap", "'" + name + "' is not a valid property name."));
         return;
     }
 
     m_element->setAttribute(convertPropertyNameToAttributeName(name), value, exceptionState);
 }
 
-void DatasetDOMStringMap::deleteItem(const String& name, ExceptionState& exceptionState)
+bool DatasetDOMStringMap::deleteItem(const String& name)
 {
-    if (!isValidPropertyName(name)) {
-        exceptionState.throwDOMException(SyntaxError, ExceptionMessages::failedToDelete(name, "DOMStringMap", "'" + name + "' is not a valid property name."));
-        return;
+    if (isValidPropertyName(name)) {
+        String attributeName = convertPropertyNameToAttributeName(name);
+        if (m_element->hasAttribute(attributeName)) {
+            m_element->removeAttribute(attributeName);
+            return true;
+        }
     }
-
-    m_element->removeAttribute(convertPropertyNameToAttributeName(name));
+    return false;
 }
 
 } // namespace WebCore