CSSValue Immediates: Replace CSSValue usage with const references

Source/core/css/RuleFeature.cpp

Index: Source/core/css/RuleFeature.cpp
diff --git a/Source/core/css/RuleFeature.cpp b/Source/core/css/RuleFeature.cpp
index 25087c5dac9b421c40f0168186eca47ab5b95bde..09c51695d6682a80178dbdb0448a3a05c2c03c6e 100644
--- a/Source/core/css/RuleFeature.cpp
+++ b/Source/core/css/RuleFeature.cpp
@@ -305,7 +305,7 @@ void RuleFeatureSet::updateInvalidationSetsForContentAttribute(const RuleData& r
         return;
 
     StylePropertySet::PropertyReference contentProperty = propertySet.propertyAt(propertyIndex);
-    CSSValue contentValue = contentProperty.value();
+    const CSSValue& contentValue = contentProperty.value();
 
     if (!contentValue.isValueList())
         return;