Make calls to AtomicString(const String&) explicit in dom/

Source/core/dom/Attr.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009, 2010, 2012 Apple Inc. All rights reserved.
  *
  * 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
@@ skipping 125 matching lines @@
         m_element->willModifyAttribute(qualifiedName(), this->value(), value);
 
     setValue(value);
 
     if (m_element)
         m_element->didModifyAttribute(qualifiedName(), value);
 }
 
 void Attr::setNodeValue(const String& v)
 {
-    setValue(v, IGNORE_EXCEPTION);
+    // Attr uses AtomicString type for its value to save memory as there
+    // is duplication among Elements' attributes values.
+    setValue(AtomicString(v), IGNORE_EXCEPTION);
 }
 
 PassRefPtr<Node> Attr::cloneNode(bool /*deep*/)
 {
     RefPtr<Attr> clone = adoptRef(new Attr(document(), qualifiedName(), value()));
     cloneChildNodes(clone.get());
     return clone.release();
 }
 
 // DOM Section 1.1.1
@@ skipping 56 matching lines @@
 }
 
 void Attr::attachToElement(Element* element)
 {
     ASSERT(!m_element);
     m_element = element;
     m_standaloneValue = nullAtom;
 }
 
 }