Change first() and second() in CSSPairValue to return const references

Source/core/css/parser/CSSPropertyParser.cpp

Index: Source/core/css/parser/CSSPropertyParser.cpp
diff --git a/Source/core/css/parser/CSSPropertyParser.cpp b/Source/core/css/parser/CSSPropertyParser.cpp
index 5c88c54ae81208312709032cb2c521cefb9ec113..d678218f2787281761258d912444ba0900a00df5 100644
--- a/Source/core/css/parser/CSSPropertyParser.cpp
+++ b/Source/core/css/parser/CSSPropertyParser.cpp
@@ -2584,10 +2584,10 @@ void CSSPropertyParser::parse3ValuesFillPosition(CSSParserValueList* valueList,
         value1.swap(value2);
 
 #if ENABLE(ASSERT)
-    const CSSValuePair* first = toCSSValuePair(value1.get());
-    const CSSValuePair* second = toCSSValuePair(value2.get());
-    ident1 = toCSSPrimitiveValue(first->first())->getValueID();
-    ident2 = toCSSPrimitiveValue(second->first())->getValueID();
+    const CSSValuePair& first = toCSSValuePair(*value1);
+    const CSSValuePair& second = toCSSValuePair(*value2);
+    ident1 = toCSSPrimitiveValue(first.first()).getValueID();
+    ident2 = toCSSPrimitiveValue(second.first()).getValueID();
     ASSERT(ident1 == CSSValueLeft || ident1 == CSSValueRight);
     ASSERT(ident2 == CSSValueBottom || ident2 == CSSValueTop);
 #endif