Have CSSFontFeatureValue store the tag as an AtomicString instead of a String

Source/core/css/CSSFontFeatureValue.cpp

 /*
  * Copyright (C) 2011 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 12 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "core/css/CSSFontFeatureValue.h"
 
 #include "wtf/text/StringBuilder.h"
 
 namespace WebCore {
 
-CSSFontFeatureValue::CSSFontFeatureValue(const String& tag, int value)
+CSSFontFeatureValue::CSSFontFeatureValue(const AtomicString& tag, int value)
     : CSSValue(FontFeatureClass)
     , m_tag(tag)
     , m_value(value)
 {
 }
 
 String CSSFontFeatureValue::customCSSText() const
 {
     StringBuilder builder;
     builder.append('\'');
     builder.append(m_tag);
     builder.appendLiteral("' ");
     builder.appendNumber(m_value);
     return builder.toString();
 }
 
 bool CSSFontFeatureValue::equals(const CSSFontFeatureValue& other) const
 {
     return m_tag == other.m_tag && m_value == other.m_value;
 }
 
 }