Fix serialization of content property to always quote

LayoutTests/fast/css/xml-lang-ignored-in-html.html

Index: LayoutTests/fast/css/xml-lang-ignored-in-html.html
diff --git a/LayoutTests/fast/css/xml-lang-ignored-in-html.html b/LayoutTests/fast/css/xml-lang-ignored-in-html.html
index 173b2f240734e344b6b0032e16471885d87473f4..34089443f173f7ba24f85a86575499e0faae5bb2 100644
--- a/LayoutTests/fast/css/xml-lang-ignored-in-html.html
+++ b/LayoutTests/fast/css/xml-lang-ignored-in-html.html
@@ -15,9 +15,9 @@ function languageOfNode(id) {
     return window.getComputedStyle(element).webkitLocale;
 }
 shouldBeEqualToString("languageOfNode('m1')", "auto");
-shouldBeEqualToString("languageOfNode('n1')", "ko");
-shouldBeEqualToString("languageOfNode('o1')", "ar");
-shouldBeEqualToString("languageOfNode('o2')", "ar");
+shouldBeEqualToString("languageOfNode('n1')", "'ko'");
+shouldBeEqualToString("languageOfNode('o1')", "'ar'");
+shouldBeEqualToString("languageOfNode('o2')", "'ar'");
 
 var successfullyParsed = true;
 </script>