Add missing break (Bug 398962) r=bzbarsky

Author: dbaron

layout/style/nsCSSRules.cpp

@@ -917,6 +917,7 @@ DocumentRule::List(FILE* out, PRInt32 aIndent) const
         break;
       case eDomain:
         str.AppendLiteral("domain(\"");
+        break;
       case eRegExp:
         str.AppendLiteral("regexp(\"");
         break;