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

Source/core/css/CSSParser-in.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 9224 matching lines @@
         return false;
     if (value->string.length() != tagNameLength)
         return false;
     for (unsigned i = 0; i < tagNameLength; ++i) {
         // Limits the range of characters to 0x20-0x7E, following the tag name rules defiend in the OpenType specification.
         UChar character = value->string[i];
         if (character < 0x20 || character > 0x7E)
             return false;
     }
 
-    String tag = value->string;
+    AtomicString tag = value->string;
     int tagValue = 1;
     // Feature tag values could follow: <integer> | on | off
     value = m_valueList->next();
     if (value) {
         if (value->unit == CSSPrimitiveValue::CSS_NUMBER && value->isInt && value->fValue >= 0) {
             tagValue = clampToInteger(value->fValue);
             if (tagValue < 0)
                 return false;
             m_valueList->next();
         } else if (value->id == CSSValueOn || value->id == CSSValueOff) {
@@ skipping 1151 matching lines @@
 {
     // The tokenizer checks for the construct of an+b.
     // However, since the {ident} rule precedes the {nth} rule, some of those
     // tokens are identified as string literal. Furthermore we need to accept
     // "odd" and "even" which does not match to an+b.
     return equalIgnoringCase(token, "odd") || equalIgnoringCase(token, "even")
         || equalIgnoringCase(token, "n") || equalIgnoringCase(token, "-n");
 }
 
 }