Make Element::attributes() less error-prone and simplify call sites

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 136 matching lines @@
 }
 
 void DatasetDOMStringMap::deref()
 {
     m_element->deref();
 }
 #endif
 
 void DatasetDOMStringMap::getNames(Vector<String>& names)
 {
-    if (!m_element->hasAttributes())
-        return;
-
     AttributeCollection attributes = m_element->attributes();
     AttributeCollection::const_iterator end = attributes.end();
     for (AttributeCollection::const_iterator it = attributes.begin(); it != end; ++it) {
         if (isValidAttributeName(it->localName()))
             names.append(convertAttributeNameToPropertyName(it->localName()));
     }
 }
 
 String DatasetDOMStringMap::item(const String& name)
 {
-    if (!m_element->hasAttributes())
-        return String();
-
     AttributeCollection attributes = m_element->attributes();
     AttributeCollection::const_iterator end = attributes.end();
     for (AttributeCollection::const_iterator it = attributes.begin(); it != end; ++it) {
         if (propertyNameMatchesAttributeName(name, it->localName()))
             return it->value();
     }
 
     return String();
 }
 
 bool DatasetDOMStringMap::contains(const String& name)
 {
-    if (!m_element->hasAttributes())
-        return false;
-
     AttributeCollection attributes = m_element->attributes();
     AttributeCollection::const_iterator end = attributes.end();
     for (AttributeCollection::const_iterator it = attributes.begin(); it != end; ++it) {
         if (propertyNameMatchesAttributeName(name, it->localName()))
             return true;
     }
     return false;
 }
 
 void DatasetDOMStringMap::setItem(const String& name, const String& value, ExceptionState& exceptionState)
@@ skipping 18 matching lines @@
     return false;
 }
 
 void DatasetDOMStringMap::trace(Visitor* visitor)
 {
     visitor->trace(m_element);
     DOMStringMap::trace(visitor);
 }
 
 } // namespace blink