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

Source/core/css/CSSParser-in.cpp

Index: Source/core/css/CSSParser-in.cpp
diff --git a/Source/core/css/CSSParser-in.cpp b/Source/core/css/CSSParser-in.cpp
index 52a25c740ccb2de8bf7f0e26e7a09647e178fd72..5e427405c1d74b0d089bd5697e02bbb76939bdb2 100644
--- a/Source/core/css/CSSParser-in.cpp
+++ b/Source/core/css/CSSParser-in.cpp
@@ -9242,7 +9242,7 @@ bool CSSParser::parseFontFeatureTag(CSSValueList* settings)
             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();